Photochromic Polymers: The Application and Control of through its Interaction with Polymers

Francesca Ercole

Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy at the University of NSW

March 2011 Abstract

This research highlights the application of polymer conjugation as a way to tailor photochromic performance. The main technology that was developed is based on targeting the local environment around the photochromic by attaching of one or more polymer tails to the molecule. Within the cured matrix this allows the dye’s mobility and switching speed to be affected in a predictable manner, as compared to the free dye. Importantly, the bulk lens matrix can be left unaltered in order to bring about the desired changes to photochromic performance. This methodology was initially applied to comprehensively tune naphthopyran switching behaviour. Naphthopyrans are a pertinent class of photochromic since they are used commercially in . ATRP (Atom Transfer Polymerization) allowed the synthesis of photochromic-polymer conjugates based on a range of polymer types and chain lengths, and therefore with different Tg’s. For the most part, a photochromic-functionalized initiator was used for the construction of the conjugates so that each dye molecule is covalently bound to the end of a polymer chain. With control over the average molecular weight and their distributions, the photochromic-polymer conjugates inherit uniform characteristics which can therefore be targeted in order to control photochromic performance. An investigation of various ATRP-produced naphthopyran-poly(n-butyl acrylate) conjugates showed that the geometry of the polymer chain is also an important consideration. This study included random copolymers and a gradient copolymer system which incorporate dye units pendant along the chains. The best system which provided superior kinetics per chain length of conjugated polymer was a Y-branching approach. This was made possible using a 2-armed photochromic initiator which locates a dye unit both pendant and exactly in the middle of two polymer chains. A related system that demonstrated the importance of targeting the dye’s local environment as a way to control photochromic performance, were films composed of ABA triblock copolymers, in which photochromic units reside in the middle of the soft central section (B). Another simple chemical strategy for making photochromic-polymer conjugates, based on a convergent methodology, is to conjugate the dye to a preformed polymer of choice. A series of flexible naphthopyran-poly(dimethylsiloxane) oligomeric conjugates

iii Abstract ______were generated as such, which showed optimized performance in a lens matrix. In a separate chapter, polyethylene glycol oligomers were also conjugated to dyes in the same manner. Schemes to synthesize the appropriate hydroxyl naphthopyrans were described. A brief study was conducted to understand the outcome of having photochromic units bound to a crosslinked and branched polymer system and the underlying factors that affect photochromic behaviour. In order to do this, various polymerizable naphthopyran monomers were synthesized and reacted firstly with the curable lens composition to become part of the network structure. Then, various crosslinked hyperbranched polymer structures were also synthesized, via RAFT, incorporating photochromic dyes either as mono-bound pendant units or as bis-tethered crosslinking agents. The behaviour of these matrix-bound systems were also compared to linear polymers. The strong sensitivity of photochromic dyes to their surroundings makes them suitable for probing studies. This approach was applied to monitor the assembly of block-copolymer micelles in water, a process that leads to measurable changes in the dye’s environment and fade kinetics. The probing study also showed that the dyes do not necessarily need to be bound to the polymer chain in order for these changes to be detectable.

iv Declarations ______

Originality Statement

I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for an award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis.

I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged.

Signed Francesca Ercole

Date 13/03/2011

v

Declarations ______

Copyright Statement

I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or hereafter known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the abstract of my thesis in Dissertations Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.

Signed Francesca Ercole

Date 13/03/2011

Authenticity Statement

I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.

Signed Francesca Ercole

Date 13/03/2011

vii

Publications ______

Publications arising from this thesis

The Application of a Photochromic Probe to Monitor the Self-Assembly of Thermosensitive Block Copolymers. Ercole F.; Harrisson S.; Davis T.P.; Evans R.A.; Soft Matter, DOI: 10.1039/C0SM00746C, 2011.

Photo-responsive systems and biomaterials: photochromic polymers, light-triggered self-assembly, surface modification, fluorescence modulation and beyond. Ercole F.; Davis T.P.; Evans R.A..; Polymer Chem., 1, 37-54, 2010. (Front Cover of Inaugural Issue.)

Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix. Ercole F.; Malic N.; Harrisson S.; Davis T.P.; Evans R.A..; Macromolecules, 43, 249-261, 2010.

Optimizing the Photochromic Performance of Naphthopyrans in a Rigid Host Matrix using Poly(dimethylsiloxane) Conjugation. Ercole F.; Malic N.; Davis T.P.; Evans R.A.; J. Mater. Chem., 19, 5612-5623, 2009.

Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation. Ercole F.; Davis T.P.; Evans R.A..; Macromolecules, 42, 1500-1511, 2009.

Publications arising outside the scope thesis

Living spontaneous gradient copolymers of acrylic acid and styrene: one-pot synthesis of pH-responsive amphiphiles. Harrisson, S.; Ercole, F.; Muir B., Polymer Chem., 1, 326-332, 2010.

Noncovalent Liposome Linkage and Miniaturization of Capsosomes for Drug Delivery. Hosta-Rigau L.; Chandrawati R.; Saveriades E.; Odermatt P.D.; Postma A.; Ercole F.; Breheney K.; Wark K.L.; Stadler B.; Caruso F. Biomacromolecules, 11, 3548-3555, 2010.

ix

Contents ______

Table of Contents

Abstract ...... iii

Declarations ...... v

Publications ...... ix

Table of Contents ...... xi

1 Introduction ...... 1 1.1 General Introduction and Aims ...... 1 1.2 Outline of Thesis ...... 2

2 Literature Review ...... 9 2.1 Photochromism – Definition and Description ...... 9 2.1.1 Mechanisms Involved in the Transformations ...... 10 2.1.2 General Photochemistry ...... 14 2.1.3 Techniques for Investigating Photochromic Transformations ...... 15 2.1.4 Photochromic Behaviour and Spectrokinetic Properties...... 17 2.1.5 Interconverting Open Isomers ...... 18 2.2 Photochromic Polymers ...... 19 2.2.1 Matrix effect ...... 19 2.2.2 Kinetic Interpretations ...... 20 2.2.3 Historical Perspective ...... 21 2.2.4 Aggregation ...... 23 2.2.5 Polarity ...... 23 2.2.6 Inorganic Hosts ...... 25 2.2.7 Method of Incorporation ...... 27 2.3 Applications ...... 29 2.3.1 Optical Data Storage and Ophthalmic Lenses ...... 29 2.3.2 Photo-responsive Polymers ...... 30 2.3.2.1 Photo-orientation ...... 30 2.3.2.2 Photo-responsive Liquid Crystals ...... 31 2.3.2.3 Photo-responsive Biomaterials ...... 34 2.3.2.4 Photo-regulation of Fluorescence ...... 43

xi Contents ______

2.4 Photochromic Polymers via Controlled Radical Polymerization ...... 44 2.5 Controlled Radical Polymerization - CRP ...... 48 2.5.1 Atom Transfer Radical Polymerization - ATRP ...... 50 2.5.2 Reversible Addition Fragmentation and chain Transfer - RAFT ...... 53 2.6 References ...... 57

3 Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation...... 71 3.1 Introduction ...... 71 3.2 Results and Discussion ...... 74 3.2.1 Polymerization - Conjugate Synthesis ...... 75 3.2.2 Optical Clarity of Test Samples ...... 79 3.2.3 Photochromic Kinetics ...... 80 3.2.4 Tuning of Decolouration Rate: Chain Length and Rigidity Affects ...... 82 3.2.5 Concurrent Influence of Local Rigidity: Colourability Evaluation ...... 86 3.2.6 Copolymerized Naphthopyran versus End-functional ...... 88 3.3 Conclusion ...... 90 3.4 Experimental Details ...... 90 3.5 References ...... 99

4 Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix...... 103 4.1 Introduction ...... 103 4.2 Results and Discussion ...... 105 4.2.1 Naphthopyran-Polymer Conjugate Synthesis...... 105 4.2.2 Evaluation of Photochromic Performance: Cast-in Lenses...... 115 4.2.3 Photochromic Films: ABA Triblock Copolymers...... 119 4.3 Conclusion ...... 122 4.4 Experimental Details ...... 123 4.5 References ...... 132

5 Optimizing the Photochromic Performance of Naphthopyrans in a Rigid Host Matrix using Poly(dimethylsiloxane) Conjugation...... 135 5.1 Introduction ...... 135 5.2 Results and Discussion ...... 136 xii Contents ______

5.2.1 Naphthopyrans ...... 136 5.2.2 Starting Materials ...... 139 5.2.2.1 Naphthols ...... 139 5.2.2.2 Propynols ...... 142 5.2.2.3 Conjugated Naphthopyrans ...... 144 5.2.3 Photochromic Properties ...... 145 5.3 Conclusion ...... 152 5.4 Experimental Details ...... 152 5.5 References ...... 175

6 Photochromic Behaviour within Polymer Matrices Part 1: Highly Crosslinked Networks ...... 179 6.1 Introduction ...... 179 6.2 Results and Discussion ...... 181 6.2.1 Photochromic Kinetics ...... 182 6.2.2 Photochromic Behaviour within Network Structure ...... 185 6.3 Conclusion ...... 191 6.4 Experimental Details ...... 192 6.5 References ...... 200

7 Photochromic Behaviour within Polymer Matrices Part 2: Hyperbranched Polymers ...... 203 7.1 Introduction ...... 203 7.2 Results and Discussion ...... 205 7.2.1 Polymer Synthesis ...... 207 7.2.2 Photochromic Behaviour ...... 211 7.3 Conclusion ...... 215 7.4 Experimental Details ...... 215 7.5 References ...... 220

8 The Application of a Photochromic Probe to Monitor the Self-Assembly of Block Copolymers in Water...... 223 8.1 Introduction ...... 223 8.2 Results and Discussion ...... 225 8.2.1 RAFT Synthesis of Polymers...... 226

xiii Contents ______

8.2.2 Thermally-Induced Self-Assembly...... 228 8.2.3 Thermal Decolouration Kinetics...... 229 8.2.4 Photochromic Probing...... 230 8.3 Conclusion ...... 238 8.4 Experimental Details ...... 238 8.5 References ...... 252

9 General Conclusions ...... 257

Acknowledgements ...... 261

Appendix 1 (Supplementary Info. for Chapter 3) ...... A1

Appendix 2 (Supplementary Info. for Chapter 4) ...... A6

Appendix 3 (Supplementary Info. for Chapter 5) ...... A14

Appendix 4 (Supplementary Info. for Chapter 6) ...... A16

Appendix 5 (Supplementary Info. for Chapter 7) ...... A18

Appendix 6 (Supplementary Info. for Chapter 8) ...... A20

xiv 1 Introduction

1.1 General Introduction and Aims

Photochromism has become an important and integral area of research, attracting interest for many high-end applications such as stimuli-responsive materials, high- density optical data storage, optical memories and switches, optical displays, non-linear , to name a few. The worldwide commercialization of T-type dyes in ophthalmic lenses is probably the most notable application as well as surface coatings, novelty items and various other light transmissible materials where dyes are added to provide UV protection and striking visual effects. A considerable amount of effort has been devoted to developing the chemistry and synthesis of photochromic dyes and certainly the last decade has seen a sharp rise in the number of publications containing comprehensive studies in solution which demonstrate the dependence of photochromic properties on electronic structure of dyes. Overall this has promoted a deeper understanding and appreciation of their unique properties. Unfortunately, an often overlooked issue is that of practically utility. For most applications, dyes normally require a solid format that is optically clear and mechanically viable. Polymers are an excellent option here since they offer robustness and clarity as a matrix with the possibility of forming films, beads, fibres, gels and mouldable items. Continued studies into photochromic polymers have been invaluable, proposing new concepts, solutions and applications for photochromism. These have evolved from a deeper understanding of how photochromics interact in a polymeric environment. The behaviour of the photochromics and polymers can be thought of as being inter- connected on many levels: the characteristics of the polymer and the mode of incorporation, whether covalent attachment or dissolution into a polymer host, can have an influence on photochromic behaviour. Micro and nano-environmental properties of polymer matrices, such as local rigidity, polarity and free volume, as well as their intermolecular interactions can all affect the efficiency and properties of the photochromic interconversions. Photo-repsonsive polymers have also shown that the photochromic transformations can also be used to influence the properties and behaviour of the polymer which incorporates them. Lastly, photochromism has also been applied to probe environmental characteristics since their behaviour is greatly influenced by what surrounds them. Chapter 1. Introduction ______

As a general concept, photochromic transitions are slower in a polymer matrix, as compared to solution. This effect is broadly attributable to the reduced segmental motion of the macromolecules and the limited free volume available in a polymeric medium. The matrix environment imposes steric constraints by limiting the mobility of the molecules and therefore their ability to isomerize. Furthermore, aggregation of molecules within solid media can also influence kinetic and spectral properties. When pertinent dyes like naphthopyran and spirooxanine dyes are included into a rigid lens matrix, this represents a very severe test of their photochromic performance. Important photochromic characteristics such as the ability to display intense and desirable colours with excellent fatigue resistance are often compromised by inefficient switching. The development of more rapid and efficient fading lenses is an area that is both commercially enticing and attracts attention from a material standpoint. Our solution to overcoming the matrix effect has been to apply concepts developed in drug and gene delivery, where polymer conjugates are used to protect the drug from a harsh biological environment. It has been found that when dyes have oligomers covalently attached to them, they are essentially insulated from the rigid lens matrix environment, since the entanglement and partitioning of polymer tails around attached dye molecules is able to provide a local environment of controlled viscosity. This technology was demonstrated for the first time by Such et al in 2004 where the photochromism of a spirooxazine was able to be controlled in a lens matrix through local environment effects. Polymer conjugation was applied using living radical polymerization (ATRP) to grow polymer chains from a spirooxazine initiator. In this thesis many of the original concepts will be extended with new ideas and methodologies by focusing on naphthopyran (chromene) dyes which are used commercially in ophthalmic lenses. The general aim of the studies will be to broaden an understanding of how these molecules interact with respect to their local environment, centralizing on how to control and apply their photochromism logically with polymers.

1.2 Outline of Thesis

Chapter 2. Literature Review. This chapter reviews the area of photochromism. It begins with a broad description into the main concepts, such as the mechanisms, the different classes of dyes, the photochemistry involved, the techniques used for investigating photochromic reactions and the analysis and interpretation of 2 Chapter 1. Introduction ______photochromic behaviour. The next section is an in-depth discussion into photochromic polymers which extends these main concepts but focuses on photochromic behaviour in polymeric environments. Important considerations are the effect of the matrix properties, such as rigidity, polarity and the method of incorporation which are all discussed. Finally, the application of photochromic polymers in literature is reviewed at length with many examples of photo-responsive systems. Overall, the discussion emphasizes the multi-faceted relationship between the photohchromic dye and the polymer that incorporates it. The use of controlled radical polymerization and its application to the synthesis of photochromic polymers is also discussed. Some of this chapter has been published as part of a review article (Photo-responsive Systems and Biomaterials: photochromic polymers, light-triggered self-assembly, surface modification, fluorescence modulation and beyond. Ercole F.; Davis T.P.; Evans R.A..; Polymer Chem., 1, 37-54, 2010, Front cover of inaugural issue).

Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation. This chapter introduces the technique of tailoring photochromic performance in a lens matrix by using novel photochromic-polymer conjugates, synthesized using atom transfer radical polymerization (ATRP), using an essentially divergent (grow-from) approach for polymer synthesis. The concept of creating a customized local environment for dye within a host matrix is applied to naphthopyrans, an important class of photochromic dyes currently dominating the commercial ophthalmic lens market. In this study naphthopyran polymer conjugates of various rigidities were synthesized by ATRP and their photochromic properties were tested within a rigid host matrix (lens). Broad tuning of photochromic kinetics was displayed as a result of polymer conjugation because of its ability to alter the local environment of the naphthopyran within the host. End- functionalized conjugates, synthesized from a naphthopyran functionalized ATRP initiator, allowed systematic tuning of kinetics via modulation of chain length of attached polymer. Reducing the rigidity of the conjugate resulted in an acceleration of kinetics and an increase in colorability. Pronounced chain lengths of poly(methyl methacrylate) (>18,000 g/mol) were required for decoloration kinetics to be effectively lowered compared with an unconjugated naphthopyran control. Random in-chain incorporation of the naphthopyran was afforded by copolymers made with naphthopyran-functionalized monomers. At the expense of a defined placement of the

3 Chapter 1. Introduction ______dye moiety with respect to the conjugated polymer chain, such conjugates displayed a pronounced ability to influence the kinetics. Persistent color due to thermally stable isomer populations was observed for all samples and found to be uninfluenced by polymer conjugation. This content of this chapter has been published (Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation. Ercole F.; Davis T.P.; Evans R.A..; Macromolecules, 42, 1500-1511, 2009).

Chapter 4. Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix. This chapter continues with the concept of applying photochromic-polymer conjugates to control photochromic behaviour but expands this idea by applying different architectures. Naphthopyran-poly(n-butyl acrylate) conjugates with different geometries were assembled using ATRP. First, within the rigid lens matrix, an investigation of the photochromic behavior of various poly(n-butyl acrylate), p(n-BA), homopolymers showed that mid-placement of a single dye moiety, made possible using a Y-branching difunctional photochromic initiator, gave superior fade kinetics per chain length of conjugated polymer compared to end-functionalized homopolymers. Furthermore, having the dye pendant from the chain opposed to directly within the chain was also found to be advantageous. Fading kinetics became faster when chain length was increased, except in the case of linear random copolymers synthesized by copolymerization of n-butyl acrylate with a naphthopyran acrylate. A gradient copolymer made with a non-photochromic difunctional initiator and a naphthopyran methacrylate displayed superior kinetics. Films consisting of ABA triblock copolymers, incorporating the photochromic in the middle of a soft p(n-BA) section, gave slower switching speeds compared to lens samples, with responses that were highly tunable and dependent on the amount of soft section inhabited by the photochromic moiety. The content of this chapter has been published (Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix. Ercole F.; Malic N.; Harrisson S.; Davis T.P.; Evans R.A. Macromolecules, 43, 249-261, 2010).

4 Chapter 1. Introduction ______

Chapter 5. Optimizing the Photochromic Performance of Naphthopyrans in a Rigid Host Matrix using Poly(dimethylsiloxane) Conjugation. This chapter introduces a simple chemical strategy for making photochromic-polymer conjugates. This is essentially a convergent approach, whereby the dye is directly conjugated to a pre-formed polymer. A series of different methoxy substituted 2,2-diaryl-2H- naphthopyran photochromic dyes were assembled incorporating hydroxyl functionality to allow their subsequent attachment to flexible poly(dimethylsiloxane) oligomers. The photochromic performance of the generated PDMS-naphthopyran conjugates was studied in a thermoset host matrix (the lens) and compared to non-conjugated, electronically equivalent control dyes. Both coloration and decolouration speeds were found to be greatly improved with critical T1/2 decolouration times reduced by 42-80%. The extent of solution-like performance provided by PDMS conjugation in the rigid host was examined with reference to the fade performance of control dyes in solution, and found to range from 20-90%. These measures are believed to be influenced by the electronic nature and steric interactions of the photochromic dyes. The content of this chapter has been published (Optimizing the Photochromic Performance of Naphthopyrans in a Rigid Host Matrix using Poly(dimethylsiloxane) Conjugation. Ercole F.; Malic N.; Davis T.P.; Evans R.A.; J. Mater. Chem., 19, 5612- 5623, 2009).

Chapter 6. Photochromic Behaviour within Polymer Matrices. Part 1: Highly Crosslinked Networks. This chapter focuses on the host matrix itself. Instead of doping a specialized photochromic-polymer into the matrix mixture, various naphthopyran dye monomers were reacted with the lens matrix composition to become part of the final crosslinked network structure and their photochromic behaviour subsequently investigated. Compared to unbound dyes (either free or polymer- conjugated), direct tethering to the rigid network was found to restrict the ability of the dyes to move and universally caused a decrease in colouration and decolouration rates. Tethering to the network structure via two reactive points located on opposite sides of the dye molecule caused a further reduction in switching speed resulting in very low levels of colouration. The fade kinetics displayed by matrix tethered dyes were also found to be more complex indicating that their local environment is less homogenous overall in the host matrix. A PEG spacer separating one tethering point from the dye allowed fade kinetics to approach those of un-tethered controls. An EG-succinate spacer

5 Chapter 1. Introduction ______that directly separates the tethering point/s from the dye itself was found to have the largest impact with longer spacers offering less improvement in speed. The position of the tethering point with respect to the dye, whether attached through the top or bottom section of the molecule, was also found to be an added complexity, significantly influencing both fade kinetics and colourability.

Chapter 7. Photochromic Behaviour within Polymer Matrices. Part 2: Hyperbranched Polymers. This chapter focuses on another crosslinked matrix system - hyperbranched polymers. Again, naphthopyran monomers were reacted within the matrix, ending up as part of the final crosslinked branched structure and their photochromic behaviour subsequently investigated. Photochromic performance was used to probe and speculate on the nature of the hyperbranched pMA and pMMA structures. The slower kinetics indicated a denser structure than expected. Longer and more flexible crosslinks are expected to provide an environment more suitable for faster switching. The content of Chapter 6 and Chapter 7 are being compiled into a combined manuscript for publication.

Chapter 8. The Application of a Photochromic Probe to Monitor the Self- Assembly of Block Copolymers in Water. The thermal decolouration response of a spirooxazine dye incorporated within several amphiphilic polymers was used to probe their self-assembly behaviour in water. Various thermally responsive poly(N-isopropyl acrylamide)-block-poly(N-acryloyl morpholine) copolymers were synthesized by RAFT polymerisation which contained the photochromic entity either as a end group or side pendant. The Arrhenius plots of thermal decolouration for each of the block copolymers in water displayed a deviation from linearity which correlated well to their thermal self- assembly profiles, as measured by DLS. The block copolymers containing spirooxazine units within the polyNIPAM section displayed the most notable deviations. The results were interpreted in terms of the effect of the environment on the transition state of the open form on progression to the closed form. The incorporation of the free dye, SOX- PROP, within the core of micelles based on poly(n-butyl acrylate)-block-poly(N- acryloyl morpholine) was also apparent from the measured decolouration kinetics. This was thought to result from the change in the local environment of the dye which occurs during encapsulation into the micelles.

6 Chapter 1. Introduction ______

The content of this chapter has been published (The Application of a Photochromic Probe to Monitor the Self-Assembly of Thermosensitive Block Copolymers. Ercole F.; Harrisson S.; Davis T.P.; Evans R.A.; Soft Matter., DOI: 10.1039/C0SM00746C, 2011.

Chapter 9. General Conclusions

This chapter collectively summarises results obtained in previous experimental chapters.

7

2 Literature Review

2.1 Photochromism – Definition and Description

The phenomenon of photochromism is defined as a reversible transformation of a chemical species between two isomeric forms, induced by the absorption of light, which results in a change of absorption spectra (colour).1 This change is reversible so that the original isomeric form can be restored by exposure to light or heat. The photochromic interconversion between isomeric forms is often referred to as switching. The system can be represented by a reversible transformation between forms A and B as shown in Figure 1.

h ( ) 1 A 1 B ( 2 )  h2 /

Figure 1. bewteen isomeric forms A and B, each having different absorption spectra.

Chemical processes involved in organic photochromism include pericyclic reactions, intramolecular hydrogen, group and electron transfers and dissociation processes. The most common photochromic systems are based on unimolecular processes like cis-trans isomerizations, compared to bimolecular systems, such as photo-dimerization reactions.2 Photochromic molecules are considered dyes due to their colourabilty and can be suitably divided into two classes depending on how form B reverts back (or decolouration) to the colourless form A: with P-type dyes the back reaction occurs exclusively with light; with T-type dyes the back reaction can also occur thermally. Other descriptive classifications are commonly used. For example, when form A is colourless or pale yellow and form B is more strongly coloured and red shifted (i.e. red Chapter 2. Literature Review ______

or blue coloured), this is referred to as positive photochromism. When max(A) >

max(B), the photochromism is referred to as inverse or negative. The observation of coloured forms before irradiation is termed reverse photochromism, compared to normal photochromism where colourless samples convert to coloured ones when irradiated. Photochromism has become a familiar term to many because of the worldwide commercial application of T-type dyes in ophthalmic lenses which are able to darken in the sun and recover transparency in diffuse light.3 Much effort has been devoted over the last half century into exploiting photochromism for a variety of aesthetic and functional applications with numerous T-type dyes commercialised along the way. A considerable portion of experimental findings has been devoted to patent literature where the dyes are exploited in an array of alternative applications. This includes surface coatings, novelty items and various light transmissible materials, mostly to provide UV protection or striking visual effects. Photochromism has also attracted research interest for other high-end applications such as stimuli-responsive materials,4 high-density optical data storage,5 optical memories and switches,6,7 optical displays,8 non-linear optics,9 to name a few. This review is focused on photochromic systems that involve the transformations shown in Figure 2, in particular those based on 2a-2c, which are notably unimolecular processes and thermally reversible. Polymeric materials play a crucial role in these studies, especially considering that many applications require materials in the form of films, sheets, plates, fibres, beads and gels, to name a few. The latter sections will therefore centralize discussion on photochromism within polymeric environments where the ability to control, exploit and understand photochromic behaviour is most important.4

2.1.1 Mechanisms Involved in the Transformations

In the dark or under typical ambient illumination are found predominantly in their more stable trans form. When irradiated with UV light this stimulates the conversion of the planar trans isomer to the bent cis isomeric form (Figure 2d). Once formed, cis isomers will thermally reconvert back to the more stable trans state in a timescale that depends greatly on their substitution pattern as well as their environment. The mechanism of isomerization has been the subject of some debate, with two pathways identified as viable: a rotation about the N-N bond, with disruption of the

10 Chapter 2. Literature Review ______

double bond, or via an inversion of the double bond through a semi-linear and 10 hybridized transition state. The isomers can be distinguished by their separate max values, however their inter-conversions are not visualized as a distinct colour change as is the case for most other photochromic transformations. Instead, at a molecular level, the isomerization leads to a substantial change in geometric conformation and size. The large geometry change can lead to motion on larger length scales which has attracted considerable attention especially in the areas of photo-responsive liquid crystals and photonics.11,12

(a) Spiropyrans -O

h1 N O NO 2 + N NO2 h2 /  Closed Form Open Form (Merocyanine) Zwitterionic (b) Spirooxazines O

N h 1 N

N O N h2 / 

Closed Form Open Form (Merocyanine) Quinoic form

(c) Chromenes / Naphthopyrans

h1 O h2 /  O Closed Form Open Form (Merocyanine) Quinoic form

(d) Azo compounds N N h1 N N

h2 / 

Cis Form Trans Form

Figure 2. Families of Organic Photochromic Compounds; h1 = (UV) light;

2 = visible (Vis) light.

11 Chapter 2. Literature Review ______

(e) Fulgides X=O and fulgimides X=NR

O O h O 1 X X h O 2 O O

Open Form Closed Form (f) and related compounds F F F F F F F F h1 F F F F Me Me h2 S S S Me S Me

Open Form Closed Form (g) Viologens

M, h ++ + R N N R R N N R M+,

(h) Triarylmethanes

h1

 R2N NR R2N NR + 2 2 - CN CN

Figure 2 (continued). Families of Organic Photochromic Compounds; 1 = ultraviolet

(UV) light; 2 = visible (Vis) light.

Spiropyrans13 and spirooxazines14 possess a spiro-carbon atom (carbon atom common to both rings) which electronically insulates half of the molecule from the other. The insulating carbon of chromenes (naphthopyrans) 15 is not combined to form a spiro heterocyclic group, and normally contains two separate unattached alkyl or aryl groups. In the initial closed form (CF/spiro) the electrons in both halves of the molecule do not interact with one another and therefore the absorption spectrum is the sum of both their spectra. On irradiation with UV light the carbon- bond is broken (heterocyclic cleavage), the insulating carbon becomes sp2 hybridized and an extensive system of conjugation is created in the molecule to generate intense colour.

12 Chapter 2. Literature Review ______

The coloured, open form of the molecule, often referred to as the merocyanine form, is able to electrocyclize back to the closed form in the absence of UV light, either thermally (in the dark) or with visible light (photochemically). In order to convert from one form to another, however, the molecules must also undergo a large intramolecular bond rotation to place the two halves of the molecules either co-planar (when coloured) or orthogonal (when clear) to one another. Substitution patterns have a marked effect on photochromic properties through steric and electronic contributions. Once formed, the merocyanine form can also interconvert between different geometrical conformations through an extra double bond rotation, leading to further complexities in switching behaviour. Spirooxazines and naphthopyrans are the most prominent of the T-type dyes because of their ability to switch many times without loss or destruction of photochromic activity, known as fatigue. Figure 3 is a three dimensional depiction of the thermal decolouration transition of a spiroxazine in solution. For diarylethenes16,17 and fulgides18,19 UV irradiation results in the closing of the six-membered ring within their core via a 2+4 electrocyclization reaction to give thermally irreversible coloured isomers. Thermal irreversibility relies on the structural features and substitution pattern of the molecules. Ring cyclization only occurs by the anti-parallel conformer, thus maximizing quantum yield depends on the ratio of anti- parallel to parallel conformers. Electron transfers (oxidation and reduction) are induced in violagens20 and heterolytic bond cleavages occur in triarylmethanes as shown in Figure 2g and 2h.

Figure 3. Three-dimensional ball and stick diagram showing spirooxazine thermal decolouration; coloured form has a planar geometry and colourless form has orthogonal conformation.

13 Chapter 2. Literature Review ______

2.1.2 General Photochemistry

When a molecule is in its ground state, electrons are predominantly in their lowest electronic state. Following excitation with electromagnetic radiation, hv, they are promoted to higher energy levels to form excited states. Their lifetime is brief with the potential for their existence to be terminated by any of several relaxation processes. The most common relaxation involves thermal deactivation by vibrational relaxation or intersystem crossing. Alternatively relaxation may take place by radiative pathways, such as fluorescence or phosphorescence or a photoreaction, as is the case for photochromism. Figure 4 is a generalized Jablonski diagram depicting the absorption of light and relaxation processes that occur, not including photchromism.

Figure 4: Generalized Jablonski diagram.52

The outcome of the deactivation is inherently associated with the kinetics of the system. In general, the process with the highest rate will take place depending on the environment (solvent, aggregates, temperature, pressure, polymeric environment). If the photochromic reaction is fast and efficient enough to overcome all other photophysical processes it must happen within the lifetime of the excited singlet or triplet state.21 In this sense, any radiative transitions can be considered competitive deactivation pathways. Figure 5 is a simplistic depiction, also in the form of a Jablosnki diagram, showing a photochromic process.

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Figure 5. Jablonski diagram exemplifying photochromism: AB quantum yield of bond cleavage on absorption of photons h; FL fluorescence from A (uncoloured form) and B (merocyanine); BA photochemical back isomerisation; kBA thermal decolouration.

2.1.3 Techniques for Investigating Photochromic Transformations

Both the rates of ‘switching to’ (colouration) and ‘switching from’ the coloured state (decolouration) are considered crucial characteristics in the study of a photochromic system. Other parameters such as the number, nature and spectral properties of transient species involved are also important. The latter are however not trivial to obtain due to the labile nature of photoproducts. Figure 6 below illustrates the possible kinetic behaviour of a unimolecular T-type photochromic transition such as that for spirooxazines, spiropyrans and naphthopyrans. A is the non-coloured closed form, M is a short lived transient species (singlet or triplet excited state or other very labile photoisomer) and B is the longer-lived but not isolatable coloured form.

Figure 6. Representation of photochromic kinetic behaviour.1

There are two main techniques that are used to investigate kinetics and associated mechanisms of photochromic reactions. One technique involves ‘flash photolysis’

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(Figure 7) which is performed by exciting the photochromic system with high-energy pulses from a laser source. This is conducted on a very fast time frame and allows only the transient species, M, to accumulate and be studied after the light pulse. Several highly sensitive detection methods can be used including time-resolved transient absorption spectroscopy, time-resolved Raman spectroscopy and time-resolved detection of emission.22-25

Figure 7. Set-up for flash photolysis studies using transient absorption spectroscopy.

The second method uses continuous irradiation with a typical set-up shown in Figure 8.26 This methodology allows monitoring over longer time scales (seconds to hours) and is too slow to effectively investigate transient species. It is a normally used for the analysis of decolouration behaviour where the coloured species B can be made to accumulate and then fade away at a measurable rate.

Figure 8. Set-up for continuous irradiation analysis.27

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The procedure is performed using a standard absorbance spectrometer, run with a kinetic programme that allows absorbance vs. time data to be collected. The decay data can be fitted to an appropriate equation (see later) to obtain kinetic parameters. For these experiments the absorbance is monitored at the max of the coloured state, firstly as the sample is irradiated with a UV light source until it reaches a photostationary state, and then as the molecules revert back to their initial colourless state in the dark, representing the thermal fade. The experiments are conducted in a temperature- controlled cell. An example of a kinetic absorption profile of a T-type photochromic, obtained using continuous UV irradiation is shown in Figure 9. The accumulation of coloured species B during UV irradiation causes the absorption density to increase; on attainment of a photostationary state the curve plateaus and then on ceasing the UV irradiation, B reverts back to colourless form A.

Figure 9. Example of photochromic curve

2.1.4 Photochromic Behaviour and Spectrokinetic Properties

The quantum yields related to the generation and disappearance of photoisomer B are also considered relavant photochromic parameters. These, however, require specially designed kinetic experiments using continuous monochromatic irradiation.28 UV/Visible multi-wavelength analysis of absorbance vs. time curves provides information about the evolution of concentrations corresponding to the species involved

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(starting compounds, photoisomers generated) which can be described by an appropriate set of differential equations. Simulated curves from the numerical integration of the differential equations generated from a kinetic scheme are then able to be compared to an experimental curve using curve-fitting procedures.29 Useful spectrokinetic methods for the investigation of photochromic transformations have recently been reviewed.30 Generic technical concerns for T-type dyes are chemical stability over a large number of cycles (fatigue resistance), colouration and decolouration speed, difference in optical density between clear and coloured states and the colour achieved. Advances in these areas are regularly reported.3 The main parameters that are normally used for describing these photochromic properties are (first order) thermal bleaching rate constants (k), colourability (A0), T1/2 (time required to reach half the initial absorbance) and colour (max of the coloured form).

2.1.5 Interconverting Open Isomers

In the last decade, studies have shown that several planar, ring-opened structures, along with several subclasses, are in fact formed on irradiation of the closed form (CF).31-35 The two main stereoisomeric classes are referred to as a trans-cis (TC) and a trans-trans (TT) merocyanine isomers, depending on the geometric arrangement of the two halves of the molecules with respect to the conjugated bridge in between. Two classes of isomeric forms can exist for each of these which represent a local energy minimum, giving TTC, CTC, TTT and CTT isomers, as shown below in Figure 10. The two main classes are known to form and decay in two consecutive steps, with TC isomers being intermediates, as in CF TC TT and TT TC CF. They each have similar absorption coefficients but markedly different thermodynamic stabilities and rates of reversion. The minor TT isomer population has the longest lifetime and the predominant TC isomers have a far shorter lifetime. For naphthopyrans, exposure to visible light is often required to fully decolourize TT isomers at ambient temperature, which normally account for 25% of the coloured state. Some dyes have also been reported to form up to 70% thermally stable coloured isomers.36-38 These phenomena have been studied using steady-state and time resolved optical absorption and emission spectroscopy.25,33,38,39 19Flourine high-resolution NMR spectroscopy has more recently corroborated the results and provided additional crucial mechanistic information on the photochemical and thermal fates of the possible

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intervening isomers.40,41 Additional thermodynamic investigations have probed the influence of substitution patterns on these processes.42,43

Spirooxazine Naphthopyran

N O N O O

O O

N N N O N O TTC TTT TTC TTT O O

O O

N N N N O O O O CTC CTT CTC CTT

Figure 10. Different interconverting stereoisomers formed with UV irradiation from a spirooxazine and a naphthopyran. TC isomers (TTC and CTC) and TT isomers (TTT and CTT).

2.2 Photochromic Polymers

2.2.1 Matrix effect

The ability of naphthopyrans, spirooxazines and spiropyrans to produce coloured forms with different absorption profiles, fading kinetics and resistance to can be modulated through substitution patterns. Comprehensive studies in literature demonstrate the dependence of photochromic properties on electronic structure, with the vast majority of these studies conducted in solution.13-15,44 On the other hand, their practical utility normally requires a solid format that is optically clear and mechanically viable.45-47 A polymeric host is an excellent option since it offers robustness as a matrix with the possibility of forming films, beads, fibres and mouldable items. The behaviour of the photochromic molecule and the polymer matrix are inter- connected on many levels: the characteristics of the polymer and the mode of incorporation, whether covalent attachment or dissolution into a polymer host, can have

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an influence on photochromic behaviour. Micro and nano-environmental properties of matrices, such as local rigidity, polarity and free volume, as well as their intermolecular interactions can also affect the efficiency and properties of the photochromic interconversions. As a general concept, photochromic transitions are slower in a polymer matrix, as compared to solution. This effect can be broadly attributed to the reduced segmental motion of the macromolecular chains and the limited free volume of a polymeric matrix, as compared to solution. The matrix environment imposes steric restraints by limiting the mobility of the molecules and therefore their ability to isomerize. Furthermore, aggregation of molecules within solid media can also influence kinetic and spectral properties. Krongauz described these aspects as the matrix effect with an investigation into the behaviour of spiropyrans and azobenzenes, with publications featuring much of the early research conducted in polymer matrices.48 Continued studies into the thermal decolouration (fade) kinetics have become invaluable allowing polymer dynamics to be probed as well as the bulk material properties to be optimized for photochromic switching.49-53

2.2.2 Kinetic Interpretations

Thermal decolouration is a unimolecular process, which in solution follows a simple mono-exponential decay that is described by first-order kinetics, as in:

kt A  Ae and ln[A]  kt  ln[A]

(where A = concentration of the coloured species decaying with rate constant k) The two different isomeric populations of open forms can be considered as decaying with two concurrent first-order processes. Therefore the decay data normally needs to be fitted to the biexponential equation (1).37,41

   k1t  k2t A A1e A2e (1)

The interpretation of photochromic kinetics in polymer media is however less straightforward. This is because the collective influences of the surrounding matrix environment introduce many complexities that need to be considered. These aspects include chain segmental mobility, the available free volume of the matrix, polarity, crystallinity, volume changes that accompany the structural changes involved in

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photochromism, how the photochromic molecules are distributed in the matrix, as well as the behaviour of the different isomers. When analyzing the decolouration behaviour of photochromics in glassy polymer matrices, a distinct departure from simple exponential kinetics is to be expected.

2.2.3 Historical Perspective

Since the first reports by Gardlund on the behaviour of spiropyrans in a poly(methyl methacrylate) (polyMMA) matrix,54 a large number of other studies have focussed on trying to elucidate the notable deviation from first-order kinetics which is seen in polymer matrices. Single exponential decays are often observed for decolouration when polymer hosts are heated above their transition temperatures (Tg) and this is reasoned in terms of the homogeneity of the molecular environment and the greater segmental motions of polymer chains.55 The internal rotations involved in the bleaching process are therefore diffusion-controlled by the matrix, and interpreted by postulating a variety of restrictive 56 environments below Tg, with a time-averaged environment existing above. Several related discussions have been proposed in the literature over the years to explain the deviation from a purely exponential decay of particular photochromic matrix systems.57,58 Richert and co-workers59,60 reasoned that photochromic reactions in glassy matrices can be described as “dispersive processes” common to a variety of kinetic phenomena in glassy materials and can been considered using a Gaussian distribution of activation energies whose width decreases with increasing temperature. The distribution of energies leads to a distribution of ln(k) around a ln(kav.), where kav is the average constant of the reaction. The two fitting parameters are kav and , which is the of the Gaussian distribution in ln(k), give a quantitative estimation for the extent of heterogeneity of the matrix. This analysis, based on the concept dispersive processes, opened new possibilities for a quantitative description of non first-order thermal reactions in glassy solids.61 Various investigators have also used a phenomenological approach to analyze thermal decay based on the Kohlraush-Williams-Watts (KWW) equation, which is often used to describe various types of non-linear relaxation processes occurring in disordered solids. The model extracts a parameter,  which represents the extent of deviation from first-order kinetics. A large change in the dispersive parameter  has been found to occur at around the Tg of the matrix, demonstrating that rigidity of the matrix is what 21 Chapter 2. Literature Review ______

dominates the dispersive nature of such processes in solids and can therefore be used to represent the molecular environmental characteristics of matrix polymers.62 Manukata analyzed quantitatively the effects of polymer matrices on the thermal decolouration of a spirooxazine using a KWW model with an emphasis on comparing them to those of solutions.63 Kryszewski rationalized the dispersive term on the basis of diffusion controlled reactions in polymer solids.64,65 The diffusion of segments in the viscoelastic state and the averaging of the free volume distribution of the matrix accounted for first-order kinetics above Tg whereas below Tg, a deviation occurs due to photochromic molecules existing in a glassy matrix made up of an unequal and discrete distribution of environments. More recently two kinetic models were applied by Levitus et al. to explain decolouration of photochromic films in the dark.66 Using a Gaussian distribution model, the polymer matrix was found to affect the width of the activation energy distribution with broader distributions found for media that were more rigid. They reasoned that this model provided a rather static picture of each polymer by assuming that it does not change during the decay process. A relaxation model was therefore also put forward to provide a mean value for the relaxation time of the matrix, taking into account the possibility of change of the environment during the decay. This model did not consider the micro-heterogeneity of solid samples, and was deemed less appropriate for describing the kinetic behaviour of highly rigid media, as compared to the intermediate range between a highly rigid polymer and a very labile, liquid-like environment. The models that have appeared in literature over the years have been applied to describe the thermal decolouration behaviour of the dyes with reference to the complexities of the solid matrices. A less absolute, yet still meaningful approach has been to fit thermal decolouration data in solid media to the bi-exponential equation (2).27 This allows quantitative comparisons to be made between decolouration kinetics in different polymers as a means to optimize photochromic performance and bypasses the mathematical expertise that is required from the other described methods.

   k1t  k 2t  A(t) A1e A2e Ath (2)

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In this model, A(t) is the optical density at max of coloured form, A1 and A2 are the contributions to the initial absorption A0, Ath is the residual colouration, accounting for residual coloured forms. In this model, molecules are decolourized with different rate constants. From the viewpoint of a uniform distribution of free volume, the separated constants k1 and k2 are understood as empirical mean values between “fast” and “slow” constants, as opposed to absolute values of decolouration for the different isomers. In some instances, the equation above allows some deductions regarding the homogeneity of the environment around the photochromic to be made by analyzing the

A1/A2 ratio. The photochromic kinetics of photochromic doped hybrid organic–inorganic matrices, have been quantified using both Gaussian and biexponential models, the latter allowing a comparison of photodynamics with those of organic polymers.27 Spirooxazine, spiropyran and naphthopyran-doped hybrid organic-inorganic matrices have been analyzed using both mono and biexponential kinetics.67,68

2.2.4 Aggregation

It is often reported that for some photochromics (namely spiropyrans and spirooxazines) the merocyanines have a strong tendency to aggregate with a stack-like arrangement.69 When the molecular dipoles of the merocyanine molecules are aligned in a head-to-head fashion they are referred to as J-stacks and their absorption spectrum is red shifted. A head-to-tail alignment, referred to as H-stacks, causes a blue-shift. Both arrangements are thought to stabilize the merocyanines involved however J-stacks are thought to be the most stable. The observed rates of decolouration have been assigned to the stabilizing influences of the different lengths of stacks. Eckhardt et al.70 used an aggregation description to explain both the spectral shifts and kinetic characteristics observed in spiropyran-doped polymer matrices on decolouring. Krongauz48 believed that merocyanine aggregates formed even in solution, with their proportions depending on temperature, concentration and also on irradiation intensity.

2.2.5 Polarity

The merocyanine form can be preferentially stabilized by polar solvents leading to a larger energy of activation and a slower rate of reversion to the closed form, compared to non-polar solvents. Occasionally, the merocyanine form can be further stabilized by related factors such as solvation, hydrogen bonding71, combinations with crown ethers

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or cyclodextrin72,73 and complexation with metals74,75. A possible consequence of enhanced stabilization is the observation of coloured forms before irradiation, termed reverse photochromism. Furthermore, spectral characteristics can also be modified Merocyanines are represented by a mixture of resonant forms in their ground state, as shown in Figure 11: either quinoid, delocalized or zwitterionic structures. Solvatochromic effects can offer insight into the governing nature of the open form. For spirooxazine and naphthopyran coloured forms, a weakly polar ground state molecule approaches the configuration of the quinoid form. This means that the transition form the ground state to the first excited state results in an increase in the dipole moment, which is normally higher for spirooxazines compared to naphthopyrans. The amount of charge separation in the excited state and sensitivity to solvation are dependant on substitution.76,77,78 As the polarity of the solvent or the matrix increases, the excited state can be stabilized relative to the ground state and the is bathochromically shifted (shifted red, to higher wavelengths). The energy barrier to colouration can also be lowered significantly, leading to thermochromism.79

Zwitterionic Delocalised Quinoid

N N N  - N - N + O + O N O

 +  O --O

NO NO NO2 2 2

- - N + O N N+ O O Figure 11. Schematic representation of the possible merocyanine structures. spirooxazines (top) naphthopyrans (middle) and spiropyrans (bottom).

The spiropyran coloured species are generally accepted to have the electronic configuration of the resonance hybrid, zwitterionic quinoidal, depending on structure, substituents and polarity of the surrounding environment.80 Research conducted by Schaudel et al.81 studied the zwitterionic nature of the spiropyran merocyanine by doping both spiropyrans and spirooxazines into a polymer matrix. The merocyanine form of the spiropyran interacted strongly with the polar

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bonds of the matrix causing stabilization of the open form over the closed form. The spiropyran merocyanine was found to be more ionic than the spirooxazine resulting in more effective stabilization. The largely zwitterionic nature of the spiropyran coloured form has been confirmed in independent studies.82,83 Polarity effects are an important factor governing photochromic kinetics and more specifically, decolouration rates within polymer matrices. Smets observed that the rate of decolouration of a spiropyran was much higher in a polystyrene (PS) than in a polyMMA host due to the higher polarity of the latter. He also observed that not only the activation energies differed considerably, but the activation entropies had opposite signs in the two matrices.84 The behaviour of methacrylate, acrylate, and styrene polymers with spiropyran side groups connected to the main chains have all been investigated with respect to polarity.85 Interestingly, polymers with low spiropyran content showed slowed rates with increased polarity, however, polymers with increased spiropyran content showed faster decolouration rates. A decrease in aggregation and interactions of spiropyran molecules with one another in the polymer coils was thought to lead to faster decolouration. Research conducted in sol-gel hybrid matrices incorporating spiropyrans and spirooxazines has also highlighted important aspects.86 In these systems the different behaviours (spectral shifts, kinetics, type of photochromism, etc) can often be explained in terms of the ground state polarity properties of the merocyanines and their interactions with the surrounding solvent/matrix.

2.2.6 Inorganic Hosts

The use of inorganic materials as host matrices for photochromic materials has been attracting increasing interest.87,88 These range from hybrid inorganic-organic composites (ormosils), to purely inorganic matrices, such as sol-gel derived silicates and aluminosilicates. The systems show strong influences on photochromc behaviour through polarity as well as steric interations with the host environment. The pores within the sol-gel frameworks are considered ideal cages for photochromic molecules. It is also possible to modify the degree of freedom of the dye molecules to different extents by grafting them to the matrix network. Within these systems, the nature and kinetics of the photochromic response depends strongly on the hydrophobic/hydrophilic balance of the hybrid material. The type of photochromic behaviour for spiropyrans trapped in organically modified sol-gel matrices was

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investigated by Levy et al.89,90 They reported that photochromic behaviour was related to the polarity of the cage within which the spiropyran was trapped. When, the cage surface was composed of apolar groups (e.g. ethyl), which did not stabilize the merocyanine form, this led to normal photochromism i.e., colourless samples convert to coloured ones when being irradiated. The materials exhibited reverse photochromism, i.e., colour in the dark and fade through the action of light, because the merocyanine zwitterionic form is stabilized by strong hydrogen bonds to the silanols of the cage. The photochromism remains normal when the spiropyran is covalently attached to the gel network by preventing the diffusion of molecules to the more polar silica zones. Biteau27 found similar behaviour for the photochromism of spirooxazine doped gels. Based on this premise, the photochromic behaviour of strongly-hydrophobic spirooxazine and spiropyran-doped sol-gel coatings was also found to be fast, normal and efficient.67 Spiroyran-modified oligomeric polysiloxanes showed preferential diffusion of polar spiropyrans to the vicinity of the polar substituents during gelation which resulted in a material that showed depressed thermal decolouration rates.91 A silylated spirooxazine was introduced into organically modified ceramic (Ormocer) coatings which also showed a reduced decolouration rate as a result of dye-to-matrix connectivity.92 Mesoporous and meso-structured composite materials have been prepared with spirooxazines located within the organic part of the composites to promote fast kinetics. Increased rates of bleaching over time indicated an ongoing reduction in the number of sites available for the open forms to stabilize.93 Stiff organic-inorganic meso-structured block-copolymer/silica composites93,94 and ceramic nano-composite coatings95 have also shown fast decolouration. Sol-gel organic-inorganic polymer hybrids incorporating spiropyran-modified poly(N,N-dimethylacrylamide) (pDMA) have also shown similar behaviour.96 Photochromic polysiloxanes with spirooxazine side groups have been investigated in which the rates of the thermal decolouration were found to be affected by spacer lengths and spirooxazine content. These were explained by the steric interactions of the bulky photochromic groups with the matrix.97 Solid polymeric siloxane resins and inorganic/organic hybrid siloxane gels incorporating bulky substituents showed significantly reduced thermal decolouration rates due to a stiff and rigid polymeric environment impeding rotational mobilty.98

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Recently photochromic sol-gel hybrid coatings were designed displaying a remarkable long-term stability of spirooxazine coloured forms in the dark. In order to stabilize the coloured form of the dye, a salt capable of forming a chelate with the open forms was incorporated into the matrix, resulting in a drastic reduction of thermal bleaching kinetics. The coloured coatings could only be reverted to their original colourless state by irradiation with visible light.99 The sol-gel method has been used to entrap different naphthopyran molecules in ormosil coatings to produce samples with a broad range of bleaching kinetics. The recovery times in the dark were found to be dependant on the dyes interaction with the polar surface of the host matrix. Molecules with a large number of substituents showed very stable open forms, approaching bi-stable systems.68,87

2.2.7 Method of Incorporation

In a very general sense, photochromic molecules can be incorporated into a polymer in two ways: either by covalent bonding to the bulk matrix or by doping/dispersing within it. The advent of controlled radical polymerization techniques in the last two decades has provided a means to synthesize photochromic-polymers with defined characteristics, offering new possibilities for use with both approaches. These strategies are discussed later. Specific studies that were focused on investigating the differences that the two approaches would have on photochromic performance were carried out as early as forty years ago. Krongauz commented that the two approaches offered little differences in terms of photochromic behaviour.100 Smets however observed differences.84 Like others,54 a drastic decrease in the rate of decolouration of a spiropyran was observed when the dye was doped in a polyMMA matrix, as compared to a homologous solvent (400 to 500 times less). However, he also found that when the dye was dissolved in a given polymeric matrix, the decolouration rate was dependent on the Tg of the polymeric matrix, but also an acceleration of the overall rate was found to correspond to a secondary transition temperature of the polymer, occurring at the point at which the mobility inside the matrix increases. On the contrary, if the dye is bonded to the polymer chain, the Arrhenius plot of the decolouration reaction showed a marked increase of overall activation energy (slope of graph) above Tg due to the additional activation energy required for viscous flow. He also found a very striking change of activation entropy values, which varied from strongly negative to highly positive values,

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101 on passing from below to above the Tg respectively. Hu et al. also found a significant difference between doped and bonded systems when they investigated kinetics over a range of concentrations. Generally, a larger modulation in kinetics was observed for the bonded-in copolymer system as opposed to the doped system (Figure 12).

Figure 12. Comparison between doped and bonded systems.101

Research conducted by Lyubimov et al.102 also supports and expands this view with investigations conducted on network polymers. Their doped model displayed single exponential decay, while the bonded model displayed multi-exponential kinetics. He reasoned that the dye molecules end up inhabiting different regions, especially with regards to homogeneity within the polymer network, and that this depends on the method used for incorporation. Interestingly, the network polymer incorporating spiropyrans cross-linked via two groups on opposite sides of the molecules showed faster kinetics compared to those containing one point of attachment per dye molecule. Even though this system would be expected to significantly restrict switching ability, it was believed to impede the more stable TT isomer population from forming. This would then allow the less stable isomers to accumulate which decolourize at a faster rate. There have been several other cases showing that the rates of thermal decay of photochromics that are bonded into glassy matrices can be larger than those observed in solution.63,103,104 Krongauz100 also showed that closely spaced photochromic groups arising in a copolymerized system can hinder the photochromic reaction by limiting the free volume needed for the photochromic transition and the segmental motion of polymer chains. Decolouration rates were found to be slower with a greater quantity of photochromics incorporated as part of the polymer or with a shorter spacer attaching the photochromic

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to the polymer backbone. Experimental results supporting these ideas were contributed by Zelichenok et al.97 and Allock et al.105

2.3 Applications

An interesting dimensional classification of matrix effects occurring within photochromic polymers was proposed by Ichimura based on the level of order of molecular structures comprising the polymeric matrices.106 Each displays a measurable optical effect, with matrices of higher dimensions exhibiting a higher level of order, such as phase-separated states and self-assembled systems. Birefringence, dichroism, circular dichroism and optical rotary power are optical manifestations arising from higher dimensional phases, which have notable application in photonic and biomedical fields. Zero dimensional order deals specifically with photochromic transformations occurring in solution and amorphous polymers. Here the primary optical changes that take place are the absorption profile (colour), emission, reflection and refraction characteristics, which are valuable to areas such as the ophthalmic lens market and optical storage media. The level of order determines the optical effect, which is therefore connected with the material’s application and end use.

2.3.1 Optical Data Storage and Ophthalmic Lenses

Photochromic dyes have become promising candidates for new high density optical recording media in which data is reversibly stored in photon mode. The multiplexing of light characteristics such as wavelength, polarization, and phase provides an opportunity for high capacity photon-mode recording systems. Photochromic materials have been applied to 3D optical recording systems based on two-photon absorption where data is written not on the material surface, but within the entire volume, resulting in increased storage density. These systems have been demonstrated using spiropyran, and dyes. Initially these were conceived using fluorescence emission as a read out method, however this often resulted in coincident loss of stored data by stimulating the photochromics to revert back to their uncoloured forms. A more promising method has been to detect the refractive-index changes that accompany the induced by long- wavelength light. So far the best candidates for are diarylethenes which are thermally irreversible therefore capable of archival storage. The various

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optical systems for reading and writing 3D memories using photochromic materials have been reviewed by Kawata.5 Commercial demand for photochromic dyes is dominated by the ophthalmic lens industry which exploits their ability to induce a marked change in colour and transmission in lens media on exposure to UV light. The dyes of choice are naphthopyran and spirooxazine dyes whose photochromic characteristics include the ability to display a broad range of intense colours with excellent fatigue resistance. As discussed previously, their photochromic inter-conversions involve substantial molecular mechanical movement, thus when included into a rigid lens matrix, this represents a very severe test of their photochromic performance. There is a commercial enticement to develop more rapid and efficient fading lenses and this area continues to motivate research efforts from polymer chemists. Our solution to overcoming the lens matrix effect has been to apply concepts developed in drug and gene delivery, where polymer conjugates are used to protect the drug from a harsh biological environment. We have found that when dyes have oligomers covalently attached to them they are essentially insulated from the rigid lens matrix environment, since the entanglement and partitioning of polymer tails around attached dye molecules is able to provide a local environment of controlled viscosity.107-111

2.3.2 Photo-responsive Polymers

A change in optical features, such as colour, is not always the most spectacular effect arising from a photochromic transformation. Within a polymeric matrix, photochromic transformations can also be exploited to reversibly alter the physical and chemical properties of a material, such as LC phase, shape, surface wettability, permeability, , self-assembly, size and fluorescence. Here the matrix effect has another meaning, which is the influence of photochromism on the matrix. Such photo- responsive systems are commonly based on polymers that incorporate photochromics within their structures, either covalently or doped.4 The following section highlights some concepts and examples regarding the use of photochromic polymers in photo- responsive materials.

2.3.2.1 Photo-orientation

For azobenzenes, the absorption of light induces molecular motion which can lead to the process of photo-orienation (Figure 13).12 When irradiated with linearly polarized

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light, an azobenzene molecule will preferentially absorb light polarized along its transition dipole axis (long axis of the molecule). Repeated trans-cis-trans isomerization cycles result in a statistical depletion of trans chromophores that lie along the polarization direction, with an eventual enrichment of those lying perpendicular. Irradiation with unpolarized light can then reverse the process by re-establishing isotropic orienation. The reversibility of the process enables subsequent photo- reorientations. The process gives rise to the optical properties of birefringence (anisotropy in refractive index) and dichroism (anisotropy in absorption spectrum), applicable to areas such as holography and reversible data storage.112,113 Birefringence and surface relief gratings have been optically induced in various forms of materials, such as polymer matrices doped with azobenzene dyes as well as amorphous azobenzene-functional polymers.114,115 Polymers doped with spiropyran, fulgide and diarylethenes have also been investigated, although azobenzene systems are by far the most studied.116,117 Aspects that affect the extent of photoinduced anisotropic orientation, the longevity and also the kinetics of orientation have all been investigated. Some polymers that have been exploited are acrylate amorphous copolymers, polyesters, polyimides and polyurethanes. These aspects have been reviewed in literature.9,11

Figure. 13. Generation of anisotropy with light: molecules excited with polarized light tend to align in a direction perpendicular to the polarization direction.9

2.3.2.2 Photo-responsive Liquid Crystals

Photochromic liquid crystal (LC) systems are known for their ability to change their long range ordering and optical properties in response to a light stimulus.8,118,119 Two

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types of photo-modulations of photochromic LC processes are possible; order-disorder phase transitions and order-order alignment changes of LC directors. Overall, the observed response of the materials to light is supported by the ability of LCs to display cooperative motion, whereby if a small portion of LC molecules change their orientation or conformation with light, this promotes other LC molecules to do the same. The response of the LC polymer to light can therefore be amplified into conversions of considerable length-scales. When a small amount of photochromic molecules, such as azobenzenes, spiropyrans and fulgides are incorporated with LC molecules and the resulting ordered mixtures are irradiated to stimulate photochromic isomerizations, a LC to isotropic phase transition can be induced isothermally. The trans-cis photoisomerization of azobenzenes incorporated in nematic LC systems are the most classically studied where the distinct transformation of molecular shape from the rod-like shape of the trans isomer, which stabilizes the phase structure of the LC, to the bent cis isomer, which acts as an impurity, results in the destruction of ordered mesophase structures (Figure 14).

Figure 14. A schematic depiction of nematic-isotropic phase transformation in a LC containing photoisomerizable mesogenic molecules, which turn from a rod-like trans to a bent cis conformation under UV.120

The photochemical phase transitions between nematic and isotropic phases (order- disorder) are thermodynamically driven and reversible with notable application in optical switching devices and information storage systems.120 Extensive investigations have been made into the photoinduced mesophase alterations of nematic LC polymers; single component copolymers containing azobenzene molecules and mesogens in the same macromolecule; polymeric liquid crystals (PLCs) doped with low molecular weight (LMW) azobenzene guests and mixtures of PLCs, LMW LCs and LMW azobenzene guests. Photochemical phase transitions in PLCs have also been induced uisng spiropyrans, spirooxazines and fulgides.121-123 Various polymers have also been

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trialled, such as azobenzene side-chain acrylates and polyesters.124 New synthetic materials have also emerged, like systems formed via hydrogen bonding125 and with novel architectures, such as dendrimers126 and block copolymers.127,128 The reorientation of the LC director can be carried out using polarized light to give an order-order change.129,130 Studies of azobenzene LC polymer systems have analyzed the factors which are important for this process, including structure of the polymer, the content and chemical nature of the photochromic moieties and the spacer lengths of the side-chains. The photo-responsive behaviour of block copolymers containing azobenzenes and other chromophores have recently been reviewed.131 These specialized systems are described as forming mesogenic phases upon the microphase separation of photoactive block sections. The supramolecular cooperative motion enables these systems to self- organize into hierarchical structures, with diverse applications in holograms, nanotemplates, photo-deformable devices and microporous films. Photochromic liquid crystal elastomers (LCE) are a relatively new class of photomechanical materials that have been developed using photochromic polymers in which large deformations can be generated in response to light stimulation. This includes reversible contractions and expansions, with changes in shape and volume. A variety of UV responsive nematic LCEs based on network structures containing different compositions and cross-linking topologies have been investigated showing contractions that were found to depend on the proportion and the position of the azobenzene units in the cross-linked polymer network.120 In addition, this photomechanical effect has also been observed in side-on nematic LCEs.132 LCE films prepared by copolymerization of an LC monomer and a diacrylate, both of which contain an azobenzene moiety, were found to yield stronger photoresponses by undergoing bending and unbending behaviour on alternate exposure to unpolarized UV and visible light. For example, a specialized LCE consisting of many micro-sized domains of azobenzene LC moieties aligned in one direction, was able to bend toward the light in the direction of light polarization.133 Palffy-Muhoray and co-workers found that by dissolving, rather than covalently bonding azobenzene dyes into a LCE sample, a mechanical deformation response was displayed to non-uniform illumination with visible light which was even larger than previously reported (>60 bending). The rapid light-induced deformations allowed the material to ‘swim’ away from the light when floating on water.134 A functional light-driven motor device was also reported by 33 Chapter 2. Literature Review ______

Ikeda and co-workers in which the rotation of a LCE belt on a homemade pulley system was able to be induced by light.135 Photo-responsive chiral photochromic PLC systems have been reviewed by Shibaev et al.136 The main system described is based on photochromic cholesteric LC copolymers which contain mesogenic groups and combined chiral-photochromic groups, as separate side-chain segments. The mesogenic fragments form the nematic phase and the chiral groups provide the twisting of the phase, to form a complex helical structure. Light irradiation and subsequent isomerization of photochromic groups bound to chiral fragments influences both the configuration and shape of these side-chain groups. With a variation of the helical twisting power, this results in dramatic changes in the optical properties of the LC polymer. Other systems described include combinations of different LC copolymers, different photochromic moieties in the same macromolecule and mixtures of LC polymers with chiral photochromic dopants. The use of light to control the pitch of helix, the rate of helix twisting and untwisting, the spectral range and the width of the selective light reflection have all been investigated. The majority of these have involved the photoisomerization of menthone derivatives as well as azobenzenes.

2.3.2.3 Photo-responsive Biomaterials

The ability to control the structure and functions of biomaterials and biomolecular processes with light is of substantial interest in the development of photo-therapies and optobioelectronic systems.137,138 A large number of efficient light-switchable systems involving photo-responsive biomacromolecules such as polynucleic acids, proteins, cellular signalling molecules and lipid systems, which find application in a broad range of biomedical fields, have all been reported. Figure 15 depicts the main approaches used for tailoring reversible photobiological switches. One approach involves the modification of biomaterials with photoisomerizable components which provides a general means to control with light the binding affinities and activities of complementary components. For instance, one photoisomeric state can block binding by distorting the biomaterial’s recognition site (Figure 15a). Such photo- regulated ‘ON–OFF’ biomaterials provide a means to design targeted therapeutic agents which can be activated and deactivated by external light signals. The binding of saccharides to concanavalin A (con A), a globular lectin protein, modified with either thiophenefulgide139 or spiropyran140 components, was able to be

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regulated reversibly by light. Azobenzene-modified papain enzyme was also able to undergo photo-regulated substrate hydrolysis.141 In these systems, regulation of binding properties originated from structural perturbations of the proteins upon photoisomerization.

Figure 15. Methods for tailoring reversible photobiological switches. (a) By covalent attachment of photoisomerizable units to the biomaterial. (b) By embedding the biomaterial in a photoisomerizable environment. (c) By using a low molecular weight photoisomerizable inhibitor. A and B are interchangeable photoisomers

Most approaches have involved attachment of the photochromic directly to a protein/peptide. Another approach is to immobilize it into a photochromic- functionalized polymer. Photoisomerization cycles can then be used to regulate its biological function. (Figure 15b). This was exemplified with the enzyme, - chymotrypsin, immobilized in a membrane made from a cross-linked acrylamide

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copolymer incorporating spiropyran units and bis-acrylamide cross-links. Activation and deactivation of the enzyme activity arose from light controlled permeability of the enzyme substrate across the polymer membrane.141 A template-directed polymerization technique, known as molecular imprinting allows receptor (binding) sites that are capable of recognizing specific molecular species to be conveniently imprinted into rigid polymer matrices. Photo-responsive molecularly imprinted polymers have been fabricated using azobenzene-based monomers incorporated into 3D cross-linked networks. Photoisomerization then regulates the release and uptake of a substrate by altering the geometry and spatial arrangement of receptor binding sites imprinted in the polymer network.142,143 Low molecular weight photochromic-functionalized enzyme inhibitors have also been designed where the geometry of one photo-isomeric state enhances affinity of the inhibitory moiety for the enzyme active site (Figure 15c). Reversible photo-regulation on a gold (Au) surface was demonstrated successfully for -chymotrypsin using an azobenzene-based inhibitor. A terminal alkyne allowed attachment to surface-bound azides using click chemistry144 and an ethylene glycol tether was used for extension of the inhibitor into solution. Significantly more enzyme was found to bind to the surface cis forms after UV irradiation.145 Shimoboji et al. developed an approach for controlling protein activity that utilizes both photo and thermo-responsive properties of copolymers incorporating azobenzene and N,N-dimethylacrylamide (DMA) components.146 These copolymer compositions displayed phase transitions within the desired temperature range of 40-45 C where the enzyme is active and thermally stable. Within this temperature range, one polymer system existed as a soluble, extended coil under UV irradiation (with azobenzene cis forms) and collapsed into a compact, hydrophobic conformation under visible light (with trans forms). A corresponding azobenzene polymer that incorporated only acrylamide-type monomers was found to switch between the two states in the opposite way. The investigators showed that the photoinduced size and hydration of the polymers, when conjugated just outside the active site of the enzyme endoglucanase, was determined by the isomeric state of the azobenzene form and could be used to regulate substrate access and subsequent hydrolysis. These photo-responsive polymers thus served to switch the polymer-enzyme conjugates ON and OFF and worked both when the conjugate was free in solution and when immobilized on beads.

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From the perspective of molecular structure, polypeptides are specialized macromolecular polymers able to exist in disordered or regularly folded arrangements, such as the -helix and -structures found in proteins. When photochromic molecules, like azobenzene or spiropyran units, are attached to polypeptides these systems can be made to respond to light by undergoing large photoinduced structural changes.147 A number of photochromic-functionalized polypeptides have been investigated as chiroptical switches in which structural changes can be induced reversibly with light via manipulation of -helix and -structures. Photochromism can result in helix reversals, random coil to -helix transitions, modulation of redox processes or a change in aggregation and disaggregation of the system, as reviewed by Feringa et al.7 In this context polypeptides containing azobenzene148,149 and spiropyran150,151 units in their side-chains, cyclic peptides and polyamide-oligomers with backbone azobenzene moieties152,153 have also been examined. The use of azobenzene cross- linking reagents to form intramolecular bridges in an engineered peptide system has been found to reversibly induce conformational changes and control helix stability upon photoisomerization.154,155 Photochromics can be anchored to polypeptides with diverse structures as a way to probe conformational dynamics of structural motifs such as protein folding mechanisms and functional aspects of specific amino-acid sequences.156 The use of light-sensitive polypeptides as intelligent molecular materials has been proposed for various applications such as micro and nanoelectronics, biomedicine, ecology, and other related areas of science.157 The photochemical control of cell adhesion has been achieved using RGD- functionalized azobenzene poly(MMA) surfaces and rationalized in terms of changes occurring in the distance of the RGD ligand from the surface via light-induced isomerizations. All peptides tested led to enhanced cell adhesion on poly(MMA) disks when azobenzenes were their trans form, whereas the plating efficiency was found to decrease with cis forms on UV irradiation by shortening the distance of the RGD- containing peptides from the surface.158 Photochromic polymers can be logically used for the design of light sensitive self- assembled delivery vehicles for biomedical areas which include micelles, vesicles, gels, nanocomposite systems and various supramolecular architectures.159,160 Surfactant and amphiphilic block copolymer micelles are commonly applied to controlled delivery systems. Light-controlled micelle disruption can be provided by incorporation of

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photochromics into the hydrophobic block (Figure 16). The photochromic transformation results in a conformational or structural change that shifts the hydrophilic/hydrophobic balance toward the destabilization of the micelles. Reversible dissociation upon illumination with UV/visible or near infrared (NIR) light has been achieved using various chromophores.128,161 The spiropyran photoconversion results in the largest change in polarity, since the merocyanine form is normally zwitterionic compared to the relatively non-polar spiro form. The azobenzene trans form is planar and non-polar compared to the cis form which has an estimated dipole moment of 4.4.162

Figure 16. A schematic illustration of block copolymer micelles that can be reversibly dissociated and formed upon absorption of light of two different wavelengths. The process is controlled by a reversible photoisomerization reaction of photochromic groups between two isomeric forms of different polarities. 161

A diblock copolymer containing, as its hydrophilic block, a random copolymer of tert-butyl acrylate and acrylic acid and an azobenzene-methacrylate as the hydrophobic block, was assembled into micelles. Upon irradiation with UV light the non-polar trans azobenzene groups were converted to the more polar cis forms, to significantly increase the hydrophilicity of the originally hydrophobic block. Therefore the micelles could be dissociated with UV light and reassembled using visible light.162,163 In a more recent example, micelles made from a block copolymer composed of poly(ethylene glycol) as the hydrophilic section and poly(spiropyran methacrylate) as the hydrophobic section displayed the same reversible dissociation using UV and visible light.164 Liu et al. reported reversible photoinduced micellization and a micelle-hollow sphere transition arising from hydrogen bonding associations in an azobenzene copolymer system.165 On the basis of photoinduced polarity change, photocontrolled and reversible swelling-shrinking behaviour of micron sized vesicles was observed,

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with a self-assembled poly(N-isopropylacrylamide), poly(NIPAM), and azopyridine- containing diblock copolymer.166 Lin et al. also reported similar photoinduced behaviour of copolymeric vesicles composed of an azopyridine-containing amphiphilic diblock copolymer. This included fusion, damage, defect formation, disruption, disintegration and rearrangements which are expected to increase the permeability of the vesicular bilayer membranes.167 The conformation and polarity of photochromic groups can have a direct influence on inter and intramolecular interactions of their copolymers and therefore also on aggregative properties. This in turn can be used to regulate permeability and transport of certain solutes, such as proteins, through the polymer network. A copolymer made from an azobenzene methacrylate and DMA was found to display significant concentration dependant photoviscosity effects in aqueous solution without macrophase separation. Trans to cis isomerization with UV light led to partial dissociation of azobenzene aggregates that acted as connective junctions. This led to a loss of viscoelasticity, especially in concentrated solutions of the polymer.168 Other amphiphilc systems have been studied, such as hydrophobically modified polymers (HMPs). These macromolecules contain alkyl side-chains on a hydrophilic backbone and undergo intra or inter-chain associations in water. Non-covalent binding associations can occur between hydrophobic moieties of the polymer as well as with amphiphilic additives, such as surfactants and proteins, leading to aggregation and gelling behaviour.169,170 Concentrated solutions of alkyl-modified poly(acrylic acid), poly(AA), can form highly viscous mixtures with proteins as a result of hydrophobic associations. Azobenzene-modified poly(AA)s (AMPs) have been studied as photo- responsive HMPs where light induced polarity changes that occur in hydrophobic side- groups can modulate aggregation and binding behaviour of the polymeric systems. Khoukh et al. reported the photo-responsive association between AMPs and non-ionic surfactants. On exposure to UV light, the formation of azobenzene cis forms weakened the association of the polymer with the surfactant.171 They also reported the reversible light-triggered control of emulsion type which could be switched from a direct emulsion (dispersion of oil droplets into the water phase) to the inverse (dispersion of water droplets into the oil phase), using poly(sodium acrylate) grafted with azobenzene units.172 The reversible photo-switching of viscosity and binding of bovine serum albumin (BSA) protein was also achieved using an aqueous solution of an AMP incorporating a few mol percent of hydrophobic moieties.173 In the dilute regime,

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BSA/polymer complexes were formed in equilibrium with unbound BSA. In the semi- dilute regime, a viscosity enhancement was obtained, ascribed to physical cross-linking of BSA with the polymer. Reversible release of BSA (by up to 80% of the protein) was obtained by exposure to UV light, due to the lower binding of cis form to the protein. Hydrogels, including cross-linked versions, consist of elastic networks able to uptake substantial amounts of water in their interstitial spaces. By incorporating photo- responsive units in these gel systems, light can be used to control swelling and shrinkage. Such volume changes of gels can be applied to actuators, sensors, controllable membranes for separations, as well as modulators for drug delivery. The triggered release of therapeutic molecules from implantable hydrogel-based devices has also been considered. A common polymer used to develop such systems is poly(NIPAM). Aqueous solutions exhibit a lower critical solution temperature (LCST) transition normally at 32 °C. Above this temperature it undergoes a volume phase transition as the solubility of the polymer is significantly reduced. This temperature depends on composition and, as a general guideline, the incorporation of more hydrophobic groups will lead to a lower LCST.174-177 For lower molecular weight homopolymer samples (normally <50, 000 g mol1), small variations in LCST have been correlated with changes in end-group structure and polarity.178 Other aspects that can influence LCST are poly(NIPAM)'s tacticity,179 architecture175 as well as solution components, such as added salts.180 A functional copolymer composed of poly(NIPAM) with a small proportion of pendant spiropyrans displayed photosensitive solubility characteristics by switching between neutral spiro and polar zwitterionic forms. Changes in the solubility of the material were also found to occur with temperature and pH.181 A corresponding cross-linked version of the copolymer displayed photo-responsive shrinking in an acidic solution and photocontrolled permeability as a porous membrane.182 Photo, thermally and pH- responsive microgel particles have also been investigated consisting of poly(NIPAM), free amine groups and spiropyran moieties as polar merocyanine forms in the dark. Visible irradiation corresponded to a reduced particle size as a result of spiropyran merocyanines reverting to less polar, closed forms. Increasing temperature resulted in a volume contraction under all light conditions and, due to the presence of amine groups, the swelling capability of the microgel was found to diminish with increasing pH.183 Dual responsive (to temperature and light), cross-linked hydrogels incorporating poly(NIPAM) and pendant spirooxazines have also been reported.184 Irradiation with

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UV light was found to enhance their water absorption and cause swelling, while an increase in temperature was found to do the opposite. In this system the spirooxazine open form is believed to be charge separated enough and has a higher dipole moment compared to its closed form, and therefore stabilized by an association with water. Rewritable microrelief formation on photo-responsive hydrogel layers composed of poly(NIPAM) and spiropyrans has been demonstrated by means of micropatterned light irradiation.185 Spiropyrans have also been found to effect dextran, such as a two-phase gel system, which exhibited reversible photoinduced phase separation.186 In a related application, photo-responsive bioconjugates have been used as tools for the specific capture of biologicals using a process of photoaffinity precipitation. An affinity macroligand was synthesized comprising poly(NIPAM) functionalized on its side- chains with azobenzene groups and at its end group with a biotin ligand. The resulting polymer showed a dependency of LCST in pure water on the isomeric state of the azobenzene groups. The precipitation of the polymer could therefore be stimulated isothermally with light, allowing the specific capture and recovery of avidin from a serum-containing cell-culture.187 The reversible changes of polarity and conformation imparted to a photochromic polymer system by photoirradiation can be applied to controlling mass transfer through porous and non-porous barriers such as membranes. Systems based on azobenzene, spiropyran and diarylethenes polymers are the most highly investigated.188 The most recent examples have focused on the control of hydrophobic/hydrophilic balance brought about by photoisomerization. The swelling degree of a membrane in water made from an amphiphilic copolymer, poly(hydroxyethyl methacrylate) functionalized with azobenzene side groups, was found to decrease with UV irradiation but could be recovered to its original level by irradiating with visible light. The decrease in the swelling degree could not be interpreted simply as a result of an increase in polarity and instead was explained by the interaction of polymer hydroxyl groups with the dipole of cis azobenzene forms. This was thought to strip away the solvating water molecules from the hydroxyl groups and consequently from the membrane.189 These functional hydrogels were extended further to show photoinduced permeation control of proteins where the polymer membrane was permeable in the dark and semi permeable to low molar mass compounds under UV irradiation due to the decreased swelling of the polymer membrane.190

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As exemplified previously, the photo-regulation of a material s function can be brought about by its immobilization in a photoisomerizable polymer. This approach, applied extensively to photo-responsive hydrogels, has also found relevance to membranes. For example, ion permeable membranes have been developed using azobenzene groups incorporated into chloromethylstyrene/divinylbenzene cross-linked polymers. Properties with respect to ion exchange capacity, water content and electrical resistance were found to change with UV irradiation. Notably, transport rates in electrodialysis of various anions were found to increase with UV irradiation. This was ascribed to the conversion of the non-polar trans forms into the more polar cis forms, which increased the water content and effective pore size of the membranes.191 A porous membrane grafted with spiropyran methacrylate and acrylamide showed an increase in permeability to a mixture of water and methanol with UV irradiation and a decrease with visible light. This was related to the extension of grafted copolymer chains, where polar zwitterionic groups caused a decrease in solubility with chain contraction resulting in more open pores.192 A macroporous polyethylene membrane coated with a copolymer carrying crown ether and spiropyran side-chains also worked as a functional membrane to control solvent permeation rate photochemically. UV light increased the polarity of membrane pores as a result of polar merocyanine forms and decreased the permeation rate of hexane. Visible light restored the permeation rate by isomerization back to the electrically neutral spiropyran form. By contrast, the permeation of ethanol was enhanced by UV light with an increase in apparent pore size as a result of polymer chain contraction and the opposite was found to occur with visible light.193 The UV-grafting of a spiropyran monomer onto a poly(ether sulfone) commercial ultrafiltration membrane also resulted in a photo-switchable membrane with reversible polarity.194 In a more recent example, the modification of the surface of nanoporous alumina membranes with mixtures of a spiropyran and hydrophobic molecules provided photocontrol over the admission of water into the membrane. When the spiropyrans existed as the less polar spiro forms the membrane was not wet by an aqueous solution. Upon exposure to UV light, the more polar merocyanine forms allowed water to enter the pores and cross the membrane. If the aqueous solution contained ions, then the membrane acted as an electrical switch to allow a current to flow, with photoisomerization leading to a two-order-of-magnitude increase in ionic conductance.195

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Surface control of hydrophilic/hydrophobic properties with light stimuli has also been used to control surface environments for attachment and proliferation of cells. The light- induced detachment of platelets and mesenchymal stem cells on glass plates coated with a copolymer containing methyl methacrylate and spiropyran units, was demonstrated upon simple and patterned UV irradiation. This also correlated with decreased water contact angles and increased water drop diameter relative to the unexposed surfaces.196 A photo-responsive culture surface which allowed photocontrol of cell adhesion was prepared with a copolymer of poly(NIPAM) with spiropyran moieties in its side-chains. Cell adhesion to the surface was drastically enhanced with polar zwitterionic forms via irradiation with UV light.197

2.3.2.4 Photo-regulation of Fluorescence

The photoinduced inter-conversion of the two states of a photochromic compound can be exploited to modulate the emission of a fluorescent partner. This photo-response can be facilitated through the Förster resonance energy transfer (FRET) process where both fluorescent and photochromic components are normally integrated within the same macromolecular or nanostructured construct. The mechanism initially involves UV irradiation to stimulate the transformation of the photochromic from a spiro closed form to a merocyanine form. This activates the energy transfer process from the excited state of the fluorophore (donor) to the merocyanine form (acceptor) thereby switching off its emission. The spectral overlap between the emission band of the fluorophore and the absorption band of the merocyanine form is therefore essential. The regeneration of the original spiro form of the photochromic allows suppression of the quenching process and switches the emission of the fluorophore back on. Thus, the emission of these systems can be repeatedly turned ON and OFF simply by switching the photochromic back and forth between its two states. Several recent reviews address the mechanisms involved in modulating the fluorescence of nanostructured constructs using photochromic switches.198,199 Using emulsion polymerization, a fluorescent dye and a spiropyran dye were able to be embedded within the hydrophobic cavities of polymeric nanoparticles composed of lightly cross-linked poly(NIPAM) and polystyrene. Using this system, photochromic switching allowed the fluorescence of the nanoparticles to be switched reversibly ON and OFF.200

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Other examples have appeared in literature, using other photochromic dyes and constructs,201,202 demonstrating that this photo-responsive system is valuable to many areas such as biomedical imaging, sensing as well as information processing and storage. Photo-responsive systems based on photochromism have generated substantial research interest, proposing a wide range of potential applications. Remarkable advances have been made over the past 30 years largely as a result of interdisciplinary efforts. It is interesting that the ability to photochromic materials are finding new opportunities in applications that in the past seemed only idealistic.

2.4 Photochromic Polymers via Controlled Radical Polymerization

As discussed above, photochromic functional polymers are extremely useful in many fields such as optical imaging, photo-responsive materials, optical data storage and light transmittable mediums such as lenses. In these applications the relationship between the photochromic moieties and the surrounding polymer environment is noteworthy on many levels. The use of free radical polymerization has become one of the most efficient tools for constructing polymers that contain covalently bound photochromics groups. Furthermore, it has become increasingly attractive to use controlled radical polymerization (CRP) techniques since these offer the ability to design polymers in a more predictable and controlled manner and with a range of architectures. The two types of living radical polymerization that are relevant to this research thesis are Atom Transfer Radical Polymerization (ATRP),203,204 and Reversible Addition-Fragmentation chain Transfer (RAFT)205-208 polymerization, the mechanisms of each are discussed in the next section. By exploiting these techniques, dyes can be introduced at different steps of the polymerization process: (i) at the very beginning via the initiator or chain transfer agent (known as -functionalization and divergent), or (ii) during the polymerization using a dye-functionalized monomer (side-functional), or (iii) via covalent binding of the dye/s to the polymer ( or end-group) after the polymer has been assembled (post- polymerization and convergent). The techniques are also invaluable by allowing dye molecules to be inserted at particular sights in the polymer chain, such as at the end, middle or as side-pendant groups in the polymer (Figure 17).

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Monomer repeat unit

T I n XYXYXY  terminator end group derived from end group, f unctional initiator e.g. trithiocarbonate (RAFT) or bromide (ATRP) or chain transfer agent

Figure 17. Structural features of a functional polymer, synthesized using controlled radical polymerization techniques (top). Examples of functional polymers (bottom).

X X X X Y end-functional telechelic di-end-functional

X X X X X X mid-functional X mid-functional side functional (junction)

The following section highlights some examples where not only the covalent attachment of the dye to the polymer is advantageous or necessary, but also the use of controlled radical polymerization for the construction of the polymer. From a basic perspective, the synthesis of well-defined photochromic polymers offers the advantage of being able to investigate and target polymer characteristics, such as composition, chain length and dye location to supply the desired optical properties. Nano-sized polymer micelles have been assembled from ABC triblock copolymers which were synthesized with ATRP,209 containing a block with pendant (side-chain) spiropyran units. The micelles behaved as a water dispersible energy transfer (FRET) system when loaded with a hydrophobic (energy donor) fluorescent dye. The overall energy transfer efficiency and fluorescence modulation of the system was found to be dependant on the length of the PS block in the triblock copolymers and only a short spiropyran block (<5 units) was found to be necessary for an efficient energy transfer process. Photo-responsive colloidal particles have been derivatized with poly(MMA) brushes containing varying concentrations of spiropyran molecules, using ATRP. UV light induced rapid aggregation of stable suspensions in toluene due to the formation of

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open and polar merocyanines. The extent of aggregation was found to depend on the spiropyran content in the polymeric brush and surrounding polarity.210 Gold nanoparticles have been successfully covered diarylethene polymers including block copolymers with styrene by using thiol end groups. These were introduced by reduction of (RAFT) dithiocarbonate groups.211 The photocyclization reactivity of the diarylethenes around the gold nanoparticles and the observed bathochromic shifts in the absorption maximum of the ring-closed forms were related back to the local electric field generated by the surface plasmon resonance of the gold nanoparticles. These depended on the chain distance between the surface of the gold nanoparticles and the diarylethene chromophore and were examined by variation of the PS block length. Using controlled radical polymerization techniques, one can design photochomic polymers in which dye moieties can be located within specialized nano-environments. A RAFT synthesized random copolymer consisting of butyl methacrylate and a methacrylate side-functionalized with spiropyrans was found to undergo UV-induced conformational changes with UV light.212 The behaviour of the photosensitive polymer in solution and adsorbed on mica was compared to the free spiropyran molecule. This was correlated to the ability of the polymer backbone to provide a less polar microenvironment for spiropyran moieties and effectively shielded them from the mica particles. Azobenzene-based polymers have continued to attract considerable attention in the scientific community due to their unique optical properties which find application in many photo-responsive systems and nonlinear optical materials. Many of these studies have focused on the guest-host systems in which various azobenzene derivatives have been utilized as dopants in conventional polymers as a way to change the polymer properties. However, owing to the poor solubility of the organic azobenzene compounds, the advantages of polymers are usually offset by the low compatibility of the azobenzene dopants within the polymer host mixture. Accordingly, azobenzene containing side-chain and main-chain polymers, which have the azobenzene groups covalently bonded within the polymers, have been increasingly considered. Recently, controlled polymerization techniques have become more commonplace in the development of such materials. Many examples have appeared in literature to show that the response of the material to light can be affected by the properties of the polymer. These effects can be most effectively examined when the properties of the polymer are well defined and characterized. ATRP was applied to synthesize a series of nonlinear

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optically (NLO) active acrylic homopolymers, containing azobenzene groups on the side-chain. The third-order NLO properties of the polymer films, including their response times, were measured and found to depend on the number-average molecular weight of polymers.213 The synthesis of a series of well defined liquid crystalline methacrylic homopolymers, containing pendant azobenzene units were prepared using ATRP. All the obtained polymeric samples showed smectic and nematic liquid-crystalline phases on heating, with phase transition temperatures and photoisomerization-induced photomechanical effects found to be strongly dependent on chain length. ATRP has also been used to produce optically active homopolymers, containing azobenzene moieties as side-chains, in order to investigate the conformational origin of chirality in this class of materials. The optical rotation and circular dichroism of the polymers was found to depend on chain-length.214 More recently, a series of well-defined linear and three- armed (star) chiral liquid-crystalline polymers were prepared which showed reversible chiroptical switching between two enantiomeric supramolecular structures obtained by irradiation with left handed or right handed circularly polarized light. The two systems were compared and it was found that branching of the macromolecular chain can act as a defect in the liquid-crystalline phase, leading to a less ordered supramolecular structure with lower chirality. Controlled radical polymerization techniques have allowed the construction of photochromic polymers with defined architectures and compositions, such as block copolymers, which have the ability to phase separate and self-assemble.215 Recently, photochromic nanopatterns were produced from the self-assembly of RAFT-synthesized poly(methylmethacrylate)-b-poly(n-butyl acrylate) block copolymers, incorporating a naphthopyran photochromic dye into the soft poly(n-butyl acrylate) section. The copolymer exhibited microphase separation into domains of controlled and regular morphology, with confinement of the photochromic dye in the soft phases to allow fast switching.216 Photo-responsive micelles have been constructed using photochromic- functionalized amphiphilic block copolymers synthesized using ATRP. These micelles are able to be reversibly dissociated and formed upon absorption of light of two different wavelengths.161 Without a doubt, the ability to exploit controlled radical polymerization techniques to synthesize engineered polymers as novel macromolecular constructs has led to new

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developments in material science and nanotechnologies and has opened up new possibilities to apply, understand and develop photochromic materials.

2.5 Controlled Radical Polymerization - CRP

Controlled (living) radical polymerization (CRP) is a powerful method for polymer synthesis and has become an important tool for the preparation of well-defined and advanced polymeric materials during the past decade.217-219 Atom Transfer Radical Polymerization (ATRP),203,204 Reversible Addition- Fragmentation chain Transfer (RAFT)205-208 and Nitroxide Mediated Polymerization (NMP)220-222 are the three major techniques implemented which provide a simple way to synthesize polymers with controlled microstructures and narrow molecular weight distributions using radically (co)polymerizable monomers (Figure 18). These techniques offer the ability to design polymers in a highly controlled fashion with a range of topologies, including not only linear homopolymers or block copolymers but also more complex architectures such as star, graft, brush and gradient copolymers (Figure 19). Controlled polymerizations can be performed in a wide range of mediums from water, through emulsion, suspension or dispersions, to inorganic surfaces. 223-226

Figure 18. Molecular weight distributions for a conventional (broad) and controlled radical polymerization (narrow).205

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linear alternating copolymer gradient copolymer

AB diblock ABA triblock ABC triblock

comb graft copolymer surface grafted

star star block microgel

X X X X X X X X X X X X X X X X multi functional hyperbranched/dendritic cyclic polymer

Figure 19. A variety of polymer architectures produced by using controlled radical polymerization.

In a broad sense, the common requirements of controlled (living) polymerization is to show a linear increase in molecular weight M n with monomer conversion, combined with a low polydispersity (PDI), (< 1.5) as shown in Figure 20 as an evolution plot of the polymerization. A first-order kinetic plot (not shown) can also serve to monitor the rate of polymerization with time, and should remain linear, at least until high conversions. A living radical polymerization process should provide controlled and predictable molecular weights, M n which can be approximated using the following equation:

M n (expected) = MW (monomer)*( [monomer] / [initiator] )*conversion

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1.6

5 104

1.4

M M /M n w n 1.2

0 1 0 20406080100 Conv. (%)

Figure 20. Evolution of molecular weight ( M n ) and polysdispersity with monomer conversion.

Another test to estimate the livingness of the polymerization is to analyze the percentage of living functional groups. Determining the amount of end groups in low molecular weight polymers can be examined using NMR, however this presents a challenge in accuracy when the degree of polymerization exceeds 100. Another useful examination that can be performed is a block extension in conjunction with GPC analysis. Here, the resulting polymer, which acts as a macroinitiator, is further polymerized with more monomer. When the living chain end purity is high, the final polymer will have increased accordingly in molecular weight.

2.5.1 Atom Transfer Radical Polymerization - ATRP

ATRP was adapted from atom transfer radical addition (ATRA), a radical technique used for adding an organic halide to an alkene utilizing a metal complex catalyst, which was discovered in 1945 by Kharasch227 and later refined by Asscher and Minisci.228 Published studies on using ATRA for controlling polymerization emerged as early as 1995 by separate research groups: Wang and Matyjaszewski,229 Kato et al.,230 Percec and Barboiu.231 The chemistry of metal catalyzed living radical polymerization has been comprehensively reviewed by Kamigaito et al.232,233 and Matyjaszewski et al.203 ATRP generally makes use of an alkyl halide (R-X) or pseudohalide234-236 as an initiator and a transition metal-ligand complex as a catalyst system. As shown in Scheme 1, ATRP involves homolytic cleavage of an R-X bond by a transition metal I complex, commonly Cu -X/L (with a rate constant ka), followed by propagation (with a rate constant kp) and reversible deactivation of the propagating chain radical (R4) (with a

50 Chapter 2. Literature Review ______

II rate constant kda) by the higher oxidation state catalyst complex (Cu -X2/L). The reaction progresses by repetitive transfer of halogen or pseudohalogen to and from the dormant chain end and the transition metal complex.203,204

Scheme 1. Generalized mechanism for ATRP.203

The components chosen for the ATRP reaction determine the equilibrium between active and dormant species, so when selected properly, this results in the preparation of well-controlled polymers with low a PDI (generally <1.5). The equilibrium constant

(KATRP = ka/kda) determines the concentration of radicals, and consequently, the rate of polymerization (Rp), the degree of termination, and the evolution of PDI. Therefore, the catalyst complex should be selected to provide a KATRP that ensures an appropriate radical concentration, an efficient deactivation of growing radicals, and a minimization of termination reactions. Various transition metals can be used in ATRP (iron, nickel, palladium, ruthenium), however copper (I) is the most efficient and the most studied.237 This transition metal binds to a ligand to form the catalyst complex. The metal-ligand complexation plays the role of solubilising the transition metal and modulating the redox potential of the Mtn / Mtn+1X cycle. Commonly used ligands are based on amines (e.g. tris[2- (dimethylamino)ethyl]amine, Me6TREN), bipyridine (bpy) and Schiff bases (e.g.. N-(n- octyl)-2-pyridinylmethanimine) systems, as illustrated below:

R R N N C H N N N N N N 8 17 N n Me6TREN bipyridine -( -octyl)-2-pyridinylmethanimine)

There are a wide range of monomers which have been successfully polymerized using ATRP, to produce a range of functional polymers.238,239 The most common ones are styrenes, methacrylates, acrylates, acrylamides and acrylonitrile.

51 Chapter 2. Literature Review ______

The initiator R-X, that is used is an activated organo halide where R is an alkyl group that bears substituents that are capable of stabilizing the formed radical and X is a labile halogen, such as Cl, Br or I. Various organo halides which are regularly exploited are -halo esters, such as ethyl 2-bromo-2-methylpropanoate and benzyl halides. Specific functionality can be introduced to the end-group of the ATRP polymer, such as a dye moiety, by using a functional ATRP initiator. The dye-modified fragment of the initiator appears at the -chain end of the polymer chain. The initiator can be synthesized in a straight forward manner such as by reacting a hydroxyl-functional dye with an -haloacyl halide, like -bromopropionyl bromide. Using this approach many ATRP initiators have been successfully used to impart sophisticated end-functionality to specific polymers238,239 such as pyrene240, flourescein241 and naphthalene242. The ATRP polymers will also contain a -terminal halogen (such as bromine) at the other end of the polymer, which can be substituted with another functional group in a post polymerization reaction.203,243 Initiators can also be synthesised which have many points of reaction, leading to telechelic, branched and star polymers.244 Polymer chains at the completion of an ATRP polymerization are active (with an active halogen), so re-initation and further growth with subsequent monomers is possible, leading to block copolymers.203,239 Overall ATRP has become a highly efficient method used for synthesizing specialized polymers for many applications.238 Nonetheless over the years, several alternative ATRP approaches have been developed in order to overcome some of the recognized limitations of the technique.245 One drawback is that the transition metal complexes can become oxidized over time to a higher oxidation state and this can lead to inconsistent results with the polymerization. This process can be minimized by using special handling procedures, such as stringent removal of oxygen from the system, careful purification of the lower- oxidation state transition metal (CuI) and special handling of a preformed catalyst 246 II complex. The use of oxidatively stable catalyst precursors, Cu -X2/L, for the polymerization are seen as an advantage industrially since they can potentially allow a more facile preparation, storage, and shipment of ATRP catalyst systems. Several alternative systems which allow the use of more stable Cu(II) complexes have therefore been investigated in literature, which make use of a free radical initiator in the polymerization mixture.247,248

52 Chapter 2. Literature Review ______

A newer ATRP system was developed that uses an electron transfer process, rather than organic radicals, for reduction and activation of a higher oxidation state transition metal complex, named activators generated by electron transfer (AGET) ATRP.245 With this approach a reducing agent, such as tin(II) 2-ethylhexanoate, is used to continuously regenerate the activating Cu(I) complex, by the in-situ reduction of the Cu(II) complex. However, another recognized drawback of these ATRP techniques was seen to be the requirement of relatively large amounts of copper catalyst (typically 0.1 - 1 mol% vs. monomer). The transition metal complexes have to be removed from the reaction mixture and preferably recycled, which can be time consuming and expensive. Recently efforts have been devoted to decrease the amount of catalyst used in ATRP systems249 which is considered beneficial both commercially and environmentally.250 A newer revised technique for conducting AGET ATRP, reworded activators regenerated by electron transfer (ARGET), was therefore developed which provides a continuous controlled polymerization but uses a significantly reduced amount of copper based catalyst complex (down to ~10 ppm).250,251 This method has been investigated successfully using various reducing agents such as tin octoate, ascorbic acid, or copper (0). The most recent advances in ATRP methods have demonstrated that alkyl dithioesters (commonly used RAFT chain transfer agents, CTAs, see below) can act as alkyl pseudohalides, i.e., ATRP initiators.252 The use of ARGET ATRP with such alkyl pseudohalides and copper catalysis is the newest system published demonstrating the recycled use of a copper wire, for the preparation of high molecular weight (co)polymers with excellent control.252-254

2.5.2 Reversible Addition Fragmentation and chain Transfer - RAFT

RAFT is a newer technique, compared to the traditional ATRP methods, which is used for the synthesis of living radical polymers, first reported in 1998 by researchers at CSIRO.255 The technique finds origins in earlier work using addition-fragmentation chain transfer agents,256-258 including macromonomers,257,259-262 allyl sulfides,263 allyl bromides,264 allyl peroxides,265 vinyl ethers266 and thionoesters.267 Several comprehensive reviews continue to be published by the many researchers using the technique.205-207,268,269 The key features of the mechanism of RAFT205,255 are a series of addition- fragmentation equilibria as shown in (Scheme 2) involving the control agent, a

53 Chapter 2. Literature Review ______

thiocarbonyl thio compound. The mechanism can be broken up into two parts: Firstly, the reversible chain transfer or pre-equilibrium step where the RAFT agent is transformed into a polymeric macroRAFT agent. This occurs with propagating radical (Pn•) which adds to the thiocarbonylthio group of 1, forming the intermediate (2) which then fragments off the leaving/reinitiating group (R•) to give the macroRAFT (3). R• reinitiates monomer forming the new propagating radical (Pm•). When the initial RAFT agent is consumed, the chain equilibration mechanism • becomes dominant, whereby (Pm ) adds to (3) giving the intermediate (4) which can rapidly equilibrate between (3) and (5), setting up a fast equilibrium between propagating radicals (Pn• and Pm•). The dormant macroRAFT agent thus provides equal opportunity for all propagating radicals to grow, thus narrowing the chain length polydispersity and providing the greater majority of chains with a thiocarbonylthio end group as well as an R group. Radicals are not formed or lost in the reversible transfer steps and thus a source of free radicals is required to initiate and maintain the polymerization, which accounts for the formation of some dead polymer, as is the case for the kinetics of conventional radical polymerization. The initial successful thiocarbonylthio RAFT agents (ZC(=S)SR) were based on dithioesters255 however the later arrivals, trithiocarbonates, dithiocarbonates (xanthates) and dithiocarbamates, have also proved successful.268,270-272 The RAFT agent’s effectiveness at CRP is strongly dependant upon the properties of the R and Z groups and on the monomer being polymerized. Also important is that the RAFT agent should have a C=S bond reactive to radical attack, the radical leaving group (R•) should efficiently reinitiate polymerization. The intermediate 2 should partition in favour of products and both intermediates 2 and 4 should fragment rapidly.96,97 The radical leaving / reinitiating group R and the activating/deactivating C=S modifier group Z should be chosen to tune the RAFT agent to suit the polymerization conditions. Efficient fragmentation for the R group is observed in substituents that are • better homolytic leaving species compared to the attacking radical Pn . Electron withdrawing groups, radical stabilizing groups and sterically bulky groups on R also enhance the rate of fragmentation of the intermediate. However, the R radical (R•) must also be able to reinitiate polymerization (Figure 21).

54 Chapter 2. Literature Review ______

initiation M M initiator I Pn

reversible chaintransfer k k add b Pn + X X R Pn X X R Pn X X + R k-add k Z Z -b Z M 1 2 3 kp

reinitiation M M M R k RM Pm i

chain equilibration k k add b Pm ++X X Pn Pm X X Pn Pm X X Pn k -add k -b Z Z Z MM k k p 3 45p

termination k t Pn + Pm dead polymer

Scheme 2. General mechanism of RAFT polymerization where X = S and Z = aryl or alkyl for dithioesters; X = S and Z = alkylthio for trithiocarbonates; X = S and Z = alkoxy for xanthates and X = S and Z = N,N-dialkylamino or N-alkyl-N-arylamino for dithiocarbamates.

Overall, when the RAFT agent is chosen correctly the process is robust, simple to perform and has minimal sensitivity to impurities. It can be used with a large range of monomers, including acid functional monomers273 and vinyl acetate.225 The process can even be done in the presence of oxygen,205 which has proven to be problematic for other living systems. It can be performed in a wide range of solvents and reaction conditions, providing control over molecular weight and giving very narrow polydispersities (usually <1.3). When the polymerization is completed (or stopped), most of the chains retain the active thiocarbonyl thio end group and can be isolated as stable materials with minimal effort. The RAFT moiety, can therefore be further re-activated for chain extension, block synthesis and complex architectural design.270,274

55 Chapter 2. Literature Review ______

The RAFT agent can also be designed to incorporate desired functionality into either (or both) the R and Z groups so that the final polymer will retain the functionalities as  and end-groups. Hence, many interesting end-functional polymers have been investigated using these methodologies.275,276 When using these approaches however, it is important to consider that functionality that has been introduced through connection to the Z group can be more easily lost through degradation of the thiocarbonyl thio end group over time whereas R-connected functionality is far for stable. Using both R and Z group approaches RAFT agents can behave as multifunctional cores, leading to the synthesis of star, hyper-branched, graft structures.277-279 Weak single bond

R' + S S R R' S S R

Reactive Z Z double bond R,R'arefreeradical leaving groups (R• must Z modifies addition and also be able to reinitiate fragmentation rates polymerization)

Figure 21. Important structural features required for a successful RAFT agent

The presence of a thiocarbonyl thio end-group in the RAFT-synthesized polymer means that the polymers will have a colour depending on the structure of the RAFT agent used, ranging from violet through to yellow. Furthermore, the polymer often has a distinct thiol odour. Dithiobenzoate RAFT and macro RAFT agents have been found to quench fluorescence, which can be an issue for optoelectronic applications.280 This has motivated research efforts into developing methods for removing the RAFT group in the final polymers or, where possible, transforming the end group post polymerization into another desired functionality. Reported methods include the use of amines, tributyltin hydride, excess AIBN281 and thermolysis.282 Several reviews focussing on end-group removal have been published.283 It is expected that controlled radical polymerization techniques, like RAFT, will continue to rise as an integral and versatile tool for the production of functional polymers. This includes light-responsive polymers, such as those integrating photochromics and for an ever-increasing range of applications such as optoelectronic and biomaterials.

56 Chapter 2. Literature Review ______

2.6 References

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(276). Chen, M.; Ghiggino, K. P.; Mau, A. W.; Rizzardo, E.; Thang, S.; Wilson, J. G. Chem. Comm. 2002, 22276-22277. (277). Moad, G.; Mayadunne, R.; Rizzardo, E.; Skidmore, M. A.; Thang, S. Macromol. Symp. 2003, 192, 1-12. (278). Barner, L.; Barner-Kowollik, C.; Davis, T. P.; Stenzel, M. Aust. J. Chem. 2004, 57, 19-25. (279). Hao, X.; Malmström, E.; Davis, T. P.; Stenzel, M.; Barner-Kowollik, C. Aust. J. Chem. 2005, 58, 483-491. (280). Farinha, J. P. S.; Relogio, P.; Charreyre, M. T.; Prazeres, T. J. V.; Martinho, J. M. G. Macromolecules 2007, 40, 4680-4690. (281). Perrier, S.; Takolpuckdee, P.; Mars, C. A. Macromolecules 2005, 38, 2033- 2036. (282). Postma, A.; Davis, T. P.; Moad, G.; O'Shea, M. Macromolecules 2005, 38, 5371-5374. (283). Willcock, H.; O'Reilly, R. K. Polym. Chem. 2010, 1, 149 - 157.

70 3 Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation.

3.1 Introduction

The increasing interdisciplinary interest in photochromic materials in the last two decades has been recognition of their practical and potential applications in a number of areas such as ophthalmic lenses, optical switches, optical filters, and temporary or permanent memory devices, to name several.1-5 The regulation of the photochromic response, observed as a reversible colour change is always of primary importance, however, a recent focus has also been the use of photochromism to simultaneously control material properties such as self-assembly and fluorescence emission.6-10 Common to many of these new photochromic applications is the use of engineered polymers. A group of photochromic molecules that has received considerable attention in industry are chromenes, also known as benzopyrans and naphthopyrans.11-13 UV irradiation of the colourless photochromic results in the electrocyclic ring opening of the pyran moiety via cleavage of the C(sp3)-O bond. This produces a distribution of isomeric open forms (merocyanines) that are intensely coloured because of their extended conjugation and quasi-planar conformations. Comprehensive NMR and time- resolved spectroscopy studies have underlined the formation of two main classes of transoid open structures, namely, transcis (TC) and transtrans (TT) geometrical isomers. These coloured isomers dominate decolouration kinetics and gradually thermally or photochemically electrocyclize back to the original closed form. Importantly, the interconversion between closed and open forms requires a large intramolecular rotation, as shown in Scheme 1.14-17 The use of diaryl-naphthopyrans in sun-protective ophthalmic lenses remains by a wide margin their largest practical and commercial application. Their chemistry has been intensely studied, and increasingly complex derivatives with additional substituents and fusion to different heterocyclic systems have been developed in order to modulate their photochromic behaviour and enhance their performance.18-26 This includes the ability to produce coloured forms with different wavelengths of absorption, resistance to photodegradation and modulation of fading kinetics. Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Scheme 1. Generic photochromic isomerization equilibrium for substituted 2,2-diaryl- 2H-naphtho[1,2-b]pyran of interest. (asymmetry at quartenary carbon results in four isomers CTC (shown), TTT (shown), TTC and CTT (not shown). The photochemical and thermal de/colouration behaviour of the molecules is profoundly influenced by the media that incorporates them. In a rigid, optically clear matrix, the ability to maintain and control photochromic switching performance is a challenge; with rigidity, viscosity, and free volume of the host environment being the major influencing factors.27-29 Efforts aimed at chemically developing dyes with predictable responses have been impressive, however, characteristics once displayed in solution are not always maintained in a solid matrix. Most design approaches are limited since optically viable host materials need to meet stringent mechanical requirements and this introduces an obvious trade-off in terms of photochromic switching. It is especially challenging considering that ophthalmic systems also contain multiple dyes which need to be synchronized in order for the lens to display desirable colour transitions. A strategy developed in our laboratory that has provided control and greater predictability over the photochromic behaviour is the use of polymer conjugation. The aim is to control kinetics effectively by neither modifying the electronic structure of the dye nor by modifying an already optimized host matrix, but instead by affecting the local environment in the vicinity of the photochromic molecule. When incorporated within a host matrix, as used for ophthalmic lenses and optical applications, entanglement and partitioning of polymer tails around covalently attached photochromic molecules creates, to varying degrees, a level of encapsulation and insulation from the bulk environment. The local environment can therefore be rationally defined by the choice of attached polymer.

72 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

The conjugation of a polymer chain to a photochromic dye can be carried out using controlled radical polymerization techniques. By using techniques such as atom transfer radical polymerization (ATRP)30 or reversible addition- fragmentation chain transfer (RAFT) polymerization,31,32 polymers with defined architectures and functionalities can be accessed with controlled molecular weights (Mn and Mw) and polydispersities (PDI = Mw/Mn) and hence, with adjustable compositions and properties. Aspects such as the ability of architecture, composition, and chain length of the attached polymer to impart a specific response to several photochromic classes continue to motivate our research efforts.5, 33-40 Since our initial report exemplifying the utility of the methodology36 other researchers have also successfully applied controlled radical polymerization techniques to their photochromic systems.10,41 The techniques can be exploited by growing a polymer from a dye-functionalized radical initiator (or RAFT agent) so that each photochromic moiety ends up covalently bound to the end of a similar polymer chain.36-39 The ability of the polymer conjugation to modify photochromic behaviour can be practically examined by variation of chain length and chain composition. Recent advances within our research group have also examined architectural modifications (end-placement of the dye vs mid-placement) to enhance and tuning of speed and impart higher colourability.40 Our research has reported the thermal decolouration behaviour of a spirooxazine photochromic dye5,36-39 in a range of environments. 2,2-Diphenyl-2H-naphtho[1,2- b]pyrans, widely known as chromenes or naphthopyrans, are pertinent dyes because of their excellent photochromic properties and commercial exploitation.42 Global studies related to these heterocyclic dyes continue to concentrate on synthetic aspects11,13,43-46 and their photophysical behaviour in solution.45,47,48 Their bulky substitution patterns suggest a large impact from their local environment, however, investigations regarding their behaviour within polymers are limited.40,41 In this work ATRP techniques were used to introduce polymer conjugation in order to investigate the influence of the local environment on the photochromic behaviour of a 2,2-diphenyl-2H-naphtho[1,2-b]pyran dye; from the rigid local environment imparted by conjugation to high Tg ( temperature) methacrylates, poly(methyl methacrylate), p(MMA) and poly(carbazolyl ethyl methacrylate), p(CEM), to the fluid- like local environment provided by poly(2-ethylhexyl acrylate), p(EHA). The ability of polymer conjugation to dominate kinetic responses and influence colourability, as well as the capacity of the host matrix to incorporate the different types

73 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______of polymer conjugates without loss of optical clarity was also presented. Furthermore, how profoundly photochromic kinetics were affected by placement of the dye pendant along the chain vs. at the end were examined. All these aspects were discussed with a view to optimizing future architectures and conjugate compositions.

Scheme 2. ATRP synthesis of naphthopyran end-functional conjugates displaying the molecular weights of purified samples that were tested; dNbpy = 4,4'dinonyl-2,2'- bipyridine, N-PPMA = N-(n-pentyl)-2-pyridylmethanimine, PMDETA = N,N,N',N',N''- pentamethyldiethylenetriamine.

3.2 Results and Discussion

To synthesize our photochromic conjugates, the preliminary requirement was a naphthopyran with a free hydroxyl group that could be made in sufficient yield for the survey. This was satisfied by the patented naphthopyran dye, 1.49 The red-colouring derivatives, 3-5, which are required for the polymerizations, and the isobutyrate control, 2, were then easily prepared from the base hydroxyl naphthopyran 1 via simple esterification routes, as shown in Schemes 2 and 3.

74 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Scheme 3. ATRP synthesis of random copolymer conjugates displaying molecular weights and compositions of purified samples that were tested; CHR refers to naphthopyran; dNbpy = 4,4'dinonyl-2,2'-bipyridine; N-PPMA = N-(n-pentyl)-2- pyridylmethanimine; PMDETA=N,N,N',N',N''pentamethyldiethylenetriamine.

3.2.1 Polymerization - Conjugate Synthesis

A series of naphthopyran conjugates, p(EHA), p(MMA), and p(CEM), of increasing molecular weight and of different rigidities were first produced (Scheme 2) using ATRP initiator 3. Then, correspondingly for each polymer type, a random copolymer comparison was also produced, as in Scheme 3, using the naphthopyran comonomers, 4 and 5. The methodologies are distinct from one another from the point of view of where the naphthopyran resides in the final polymer chains: the first precisely places the dye at the end of each polymer chain in comparison with the latter that randomly incorporates the naphthopyran moieties pendant along the chains (in-chain vs. end-of chain). All conjugates were compared with the electronically equivalent isobutyrate control 2 to allow the effect of the conjugation to be displayed.

75 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

The ATRP polymerizations of the end-functional naphthopyran conjugates were monitored to gauge the viability of ATRP conditions and then applied to generate the corresponding copolymer samples. The EHA polymerizations were carried out using CuBr and the 4,4-dinonyl-2,2-bipyridine (dNbpy) catalyst system at 90 °C. Polymerizations proceeded effectively with low PDIs throughout and with only minor deviations from expected molecular weight (Figure 1). Furthermore, the first-order kinetic plot displayed a near-linear relation with time (Appendix 1, page A2). MMA polymerizations were carried out using a Haddleton ligand, N-(n-pentyl)-2- pyridylmethanimine (N-PPMA)50 and CuBr in toluene at 90 °C. As shown in the p(MMA) evolution plot (Figure 2), the ATRP polymerization proceeded well with molecular weights (Mn) increasing linearly with conversion, even up to >90%, so that controlled samples with higher Mn values could be accessed. The first-order kinetic plot showed linearity up until such high conversions with a brief induction period at the beginning of the polymerization (Appendix 1, page A1). The CEM polymerizations (Figure 3) proved to be more challenging. Using the N- PPMA/CuBr catalyst system, the polymerization was initially slow, yet still showed a controlled growth with time. However, the first-order kinetic plot clearly shows that after 5 h of slow polymerization, the rate of polymerization dramatically changed to give higher conversions (>60 %) with broadened PDIs (>1.3) (Appendix 1, page A1). It is believed that the reduced solubility that was observed at this point resulted in an inhomogeneous monomer distribution and non-linear rate of polymerization with time. In any case, I found that the p(CEM) conjugates formed at this point, which had higher

Mn values >14,000 g/mol, could not be used for photochromic testing because they subsequently formed test samples that lacked optical clarity. Another CEM polymerization trial was therefore carried out with a more active catalyst system that supplied samples of lower molecular weights during the polymerization time, Mn = 10,600 and 12,100 g/mol, albeit with slightly higher polydispersities.

The composition and Mn of copolymers 9-11, as shown in Scheme 3, were 1 determined by H NMR and GPC, respectively. Because the polymers had Mn values similar to those of corresponding end-functional conjugates (7b, 8d, and 6c), these provided insightful comparisons for assessing the effect of dye location on photochromic kinetics. Assigned 1H NMR spectra are included in Appendix 1 for reference and the polymerization characteristics of all the conjugates tested are shown in Table 1.

76 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Table 1. Polymerization Characteristics of Naphthopyran-Polymer Conjugates Tested.

a b c d Sample Time (mins) Conv. (%) exp. Mn theo. Mn PDI 6a 60 7 1,900 1,880 1.08 6b 60 22 6,300 6,165 1.24 6c 120 39 12,000 10,700 1.17 7a 120 16 4,900 3,790 1.12 7b 240 49 11,800 10,300 1.09 7c 370 66 16,400 13,800 1.12 7d 480 74 19,200 15,400 1.12 7e 540 76 19,800 15,805 1.12 7f 960 90 23,500 18,610 1.23 8a 180 9 4,000 3,210 1.20 8b 240 14 4,300 4,580 1.21 8c 300 20 5,400 6,240 1.25 8d 90 60 10,600 17,350 1.27 8e 180 76 12,100 21,820 1.27 9e 960 70 12,500 15,350 1.29 10e 120 63 9,500 17,650 1.27 11e 570 50 10,400 9,532 1.12 a Polymerization for 6a performed with 2-(ethylhexyl acrylate) at 90 °C in bulk where [monomer]/[CuBr]/[4,4’-dinonyl-2-2’-bipyridine]/[3] = 100:1:2:1; Polymerizations for 6b and 6c performed with 2-(ethylhexyl acrylate) at 90 °C in bulk where [monomer]/[CuBr]/[4,4’-dinonyl-2-2’-bipyridine]/[3] = 150:1:2:1; Polymerizations for 7a-7f performed with methyl methacrylate at 90 °C in toluene where [monomer]/[CuBr]/[N-(n-pentyl)-2-pyridylmethanimine]/[3] = 200:1:2:1; Polymerizations for 8a-8c performed with 2-(9H-carbazol-9-yl)ethyl methacrylate at 90 °C in toluene where [monomer]/[CuBr]/[N-(n-pentyl)-2-pyridylmethanimine]/[3] = 100:1:2:1; Polymerizations for 8d and 8e performed with 2-(9H-carbazol-9-yl)ethyl methacrylate at 90 °C in toluene where [monomer]/[CuBr]/[N,N,N',N',N''- pentamethyldiethylenetriamine]/[3] = 100:1:1:1; Polymerization for 9 performed with methyl methacrylate and 4 (98:2) at 90 °C in toluene where [monomers]/[CuBr]/[N-(n- pentyl)-2-pyridylmethanimine]/[ethyl-2-bromoisobutyrate] = 200:1:2:1; Polymerization for 10 performed with 2-(9H-carbazol-9-yl)ethyl methacrylate and 4 (94:6) at 90 °C in toluene where [monomers]/[CuBr]/[N,N,N',N',N''-pentamethyldiethylenetriamine/[ethyl- 2-bromoisobutyrate] = 100:1:1:1; Polymerization for 11 performed with 2-(ethylhexyl acrylate) and 5 (97:3 molar ratio) at 90 °C in toluene where [monomers]/[CuBr]/[4,4'- dinonyl-2,2'-bipyridine]/[ethyl-2-bromoisobutyrate] = 100:1:2:1. b Determined by 1H NMR analysis of polymerization mixture. c Determined by GPC (THF) for 6a-6c and 11 in poly(2-ethylhexyl acrylate) equivalents using Mark-Houwink parameters on a PS calibration; for 7a-7f and 9 calibration with p(MMA) standards and for 8a-8e and 10 PS standards used for calibration. d Calculated based on monomer conversion plus initiator molecular weight. e Final composition of copolymers estimated by integration ratios of naphthopyran proton of vs. that of comonomer. Final compositions shown in Scheme 3, 1H NMRs displayed in Appendix 1.

77 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Figure 1. Evolution of polydispersity () and molecular weight () with conversion for the ATRP of 2-(ethylhexyl acrylate) at 90 °C in bulk where [monomer]/[CuBr]/[4,4- dinonyl-2,2-bipyridine]/[3] = 150:1:2:1. Calculated molecular weight (----) by NMR conversion using equation: Mn = ((monomer MW)*([monomer]/[3])*(NMR conversion)) + (MW of 3). Polymerization times ranged from 1-7 hrs.

Figure 2. Evolution of polydispersity () and molecular weight () with conversion for the ATRP of methyl methacrylate at 90 °C in toluene where [monomer]/[CuBr]/[N-(n- pentyl)-2-pyridylmethanimine]/[3] = 200:1:2:1. Calculated molecular weight (----) by NMR conversion using equation: Mn = ((monomer MW)*([monomer]/[3])*(NMR conversion)) + (MW of 3). Polymerization times ranged from 2-16 hrs.

78 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Figure 3. Evolution of polydispersity () and molecular weight () with conversion for the ATRP of 2-(9H-carbazol-9-yl)ethyl methacrylate at 90 °C in toluene where [monomer]/[CuBr]/[N-(n-pentyl)-2-pyridylmethanimine]/[3] = 100:1:2:1. Calculated molecular weight (----) by NMR using equation: Mn = ((monomer MW)*([monomer]/[3])*(NMR conversion)) + (MW of 3). Polymerization times ranged from 3-6 hrs.

3.2.2 Optical Clarity of Test Samples

Photochromic test samples were prepared by firstly adding the photochromic conjugates (or control 2) individually to the lens monomer formulation at a set concentration level. A level of 1.5 × 107 mol per gram of host matrix composition was used for the control and all end-functional conjugates. Variable quantities of the copolymers were added to account for non-equivalent numbers of dye moieties being present per chain. The host formulation was composed of poly(ethylene glycol) 400 dimethacrylate (PEGDMA) and 2,2-bis(4-methacryloxyethoxy)phenyl propane (otherwise known as ethoxylated bisphenol-A dimethacrylate, EBPDMA) in a 1:4 weight ratio and azobis(isobutyronitrile) (AIBN), 0.4% by mass. The formulations were mixed thoroughly with the photochromic-polymer conjugates and thermally cured in a mould to produce optically clear test samples of the an equivalent thickness. It is envisaged that as the host material polymerizes to form the bulk matrix during the curing process, the polymer attached to the photochromic moiety coils and entangles, to varying degrees, around dye molecules and their aggregates. Therefore, the ability to regulate the photochromic response relies on the interaction of the dye with

79 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______the conjugated polymer. From the perspective of the dye molecule, conjugation creates an overall encapsulation effect. In addition to this general description, the formation of distinct phases or domains within the host which contain a collection of polymer chains is also a possibility but this remains difficult to determine, especially considering the low doping levels that are used. Nonetheless, if distinct phases are indeed formed, these need to be confined to the nano-scale (ca. <200 nm) so that samples remain optically transparent (i.e. not cloudy/hazy) and not interfere with photochromic measurements. Whilst reducing the miscibility of the polymer tail with the host acts to promote encapsulation of dye molecules, it must also be kept to a level that does not cause gross and visibly-obvious phase separation. An important requirement for a test sample which incorporates a photochromic conjugate is therefore a high level of optical clarity. I have found that the chemical composition, chain length of the polymer conjugate, and concentration within the host are all associated factors that affect this. These aspects continue to be monitored. Within this investigation several conjugate types were provided for testing. It was found that all p(MMA) conjugates (7a-7f and 9) of a broad Mn range (up to 24,000 g/mol) could be incorporated into the host matrix at the desired concentration level. This was also the case for the p(CEM) conjugates (8a-8e and 10). Out of the p(EHA) conjugates synthesized, only the lower Mn conjugates (6a and 6b) could be successfully incorporated into the host at the desired concentration level. Samples 6c and 11 displayed mild phase separation and were therefore doped at half of the concentration to allow testing.

3.2.3 Photochromic Kinetics

The thermal decolouration of the naphthopyran test samples was investigated in the dark at 20 °C after continuous UV irradiation. As depicted in Scheme 1, exposure of the original closed form (CF) to continuous irradiation with UV light establishes a photosteady state made up of an equilibrium distribution of coloured merocyanine isomers. This is displayed as a levelling-out of the absorbance value in the colouration curve. The two main classes of merocyanine isomers (transoid cis, TC) and transoid trans, TT) are produced in consecutive steps and have similar absorption spectra but different thermodynamic stabilities and activation properties for isomerization (enthalpies and entropies), as elucidated by several NMR studies.14-16

80 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Figure 4. Absorption spectra of naphthopyran 2 in host matrix before (black) and after 2 minutes of UV irradiation (red).

As an example, Figure 4 shows the absorption profile of the control naphthopyran dye 2 before and after UV exposure. Photochromic kinetics are studied by monitoring the absorption value at the max of the open form with time. The decay data measured during thermal bleaching (decolouration) is then fitted to the following empirical equation,16,51    k1t  k2t  A(t) A1e A2e Ath where A(t) is the optical density at max of the open forms; A1 and A2 are the contributions to the initial optical density, A0; k1 and k2 are exponential decay rate constants of fast and slow components, respectively; and Ath is the residual colouration (offset) at the end of the testing time. Simple exponential decolouration behaviour in solution (either biexponential or monoexponential with a residual term) can be attributed to the two main classes of coloured merocyanines decaying with disparate first-order rate constants. Solid matrices contain a distribution of environments, such as free volume and porosity, as opposed to the monodisperse environment of a solution and this can also affect kinetics. Therefore, the separated constants, k1 and k2, in the equation above, along with their allocated contributions to initial optical density, are understood as overall empirical values between notable fast and slow kinetic components. The equation has been previously used to represent and compare the decolouration behaviour of both spirooxazines and naphthopyrans within solid media41, 51, 52 and has consistently fitted our decolouration 36,38-40 curves with correlation coefficients (R) of greater that 0.99. Measured T1/2 values

81 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

(time to fade to half of the initial absorbance value) are also beneficial for comparing overall kinetics. The kinetic data for the thermal decolouration of all naphthopyran conjugate test samples and the control dye 2 are shown in Tables 2 and 3.

3.2.4 Tuning of Thermal Decolouration Rate: Chain Length and Rigidity Affects

The kinetic survey of naphthopyran conjugates commenced with a brief review of the decolouration performance of the low Tg p(EHA) conjugates that could be incorporated into the host matrix. I also compared their performance to that of the control dye 2 in solution as well as in the matrix (Table 2 and Figure 5).

As in solution, all of the samples tested (including the high Tg conjugates described below) produced a persistent coloured isomer population with normalised decolouration curves converging to similar residual values (Ath). It was found that as with many other chromene/naphthopyran dyes, this isomer population could only be fully removed photochemically with exposure to visible light and can be attributed to more thermally stable TT-type isomers.14

Table 2. Photokinetic analysis of decolouration of poly(2-ethylhexyl acrylate)- naphthopyran conjugates relative to the control naphthopyran 2 in host matrix.a

b c d -1 -1 e sample max Mn A0 k1 (min ) A1 k2 (min ) A2 Ath T1/2 (s)

2 (tol.) f 483 1.22 0.91 0.72 0 0 0.23 63

2 500 - 0.96 0.59 0.55 0.07 0.16 0.27 173

6a 496 1,900 1.25 0.82 0.66 0.13 0.08 0.24 89

6b 492 6,300 1.10 0.90 0.73 0.07 0.03 0.22 70

6cg 477 11,700 0.58 0.86 0.71 0 0 0.26 73

11 484 10,400 0.95 0.94 0.74 0.03 0.03 0.21 64

a Host = PEGMA:EBPDMA 1:4 mass composition, samples initially irradiated at 350-400 nm for 1000 seconds, then thermal decolouration monitored at max of the coloured form at 20 °C in the dark for 4800 seconds. b in nm and pre-determined by c wavelength scan of coloured form. Molecular Weight, Mn, (in g/mol) of purified conjugates estimated from GPC analysis: poly(2-ethylhexyl acrylate) equivalents obtained using Mark-Houwink parameters on a PS calibration. d Measured absorbance intensity at onset of thermal decolouration period. e Time taken for the initial f -5 -kt absorbance value, A0, to decay to half. 1 ×10 M in toluene, fitted to A(t) = A1e + Ath. g Conjugate doped at half std. concentration (0.75 × 10-7 mol/g) due to mild phase separation in the host.

82 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Figure 5. Normalised thermal decolouration curves of poly(2-(ethylhexyl acrylate)- naphthopyran conjugates 11, 6b, 6a and control 2 in host matrix, compared to the control 2 in toluene (monitored in the dark at 20 °C after UV irradiation for 1000 seconds).

As expected, the low Tg conjugates displayed accelerated switching speeds in the rigid host matrix with respect to control 2 (Figure 5). This was apparent even for the lower Mn value sample, 6a (<2,000 g/mol), and with a modestly higher Mn value of 6,300 g/mol, 6b showed decolouration behaviour that closely approached that of the control in solution (T1/2 value of 63 s for 2 in toluene vs. 70 s for conjugate 6b in the matrix). In previous investigations regarding n-butyl acrylate naphthopyran40 and 38 spirooxazine end-functional conjugates, higher Mn values were required to induce the same increases in kinetics with respect to their controls. This is to be expected from longer aliphatic and branched side chains providing a stronger lubricating effect on the dye’s local environment. An inspection of the fitted kinetic data (Table 2) also reveals a diminishing contribution term (A1) along the series for the slower kinetic component, k2 so that 6c could be fitted to the simplified exponential kinetics displayed by 2 in solution. The p(EHA) conjugates also displayed increasingly significant hypsochromic shifts in their absorption spectra in the host matrix, as much as 23 nm for sample 6c and 16 nm for copolymer 11, as compared to control 2. Naphthopyrans have a weakly polar ground state that approaches the configuration of a quinoidal form so that the transition to their first excited state results in an increase in the dipole moment. Therefore, an increase in the medium polarity can result in preferential stabilization of the excited state relative to the ground state with absorption bands shifted accordingly.53,54 The 83 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______hypsochromic shifts that were seen for 11 and 6b (484 and 492 nm) can be ascribed to the naphthopyran moieties being effectively insulated from the more polar matrix environment, which contains substantial PEG units, as a result of conjugation to p(EHA). This is particularly evident for 11 which displayed the largest shift. These factors (both kinetic enhancements and shifts in wavelength of coloured form) all suggest a pronounced level of encapsulation offered by p(EHA) conjugation.

Nevertheless, the low Mn range for the end-functional conjugates that could be incorporated within the matrix means that the kinetic enhancement and tuning ability offered by this polymer system is relatively limited. The capacity for the methacrylate polymers, p(MMA) and p(CEM), to add rigidity to local domains was first confirmed by their high Tg values (shown in Table 3); the bulky carbazole side groups of p(CEM) conjugates are able to impart further stiffness and rigidity to local domains, beyond that of p(MMA).55 Since the testing temperature

(20 °C) of the lenses was far below the measured Tg values of the photochromic- polymer conjugates, one would expect a significant restriction in photochromic movement within entangled chains. Previous research into the behaviour of end- functional spirooxazine high Tg polymer conjugates, namely p(MMA) and p(styrene), showed that the rates of thermal decay could be systematically reduced with increasing chain length of the attached tail.36,37 Analogously, a similar pattern was observed here with naphthopyran dye conjugates, 7a-7f and 8a-8e.

Figure 6. Thermal decolouration curves (monitored in the dark at 20 °C after UV irradiation for 1000 seconds) of various methacrylate naphthopyran end-functional conjugates and control 2 in host matrix.

84 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Chain length plays a dominant role in generating increasingly restrictive domains for the photochromic transitions resulting in systematically increasing T1/2 values and decreasing rates of decolouration for both polymer types. However it was evident by comparing normalised decolouration curves that for this already slow photochromic dye, high Tg tailing did not universally produce slower kinetics in the host matrix compared to the control (see Figure 6); in fact, this was only established at a pronounced molecular weight of p(MMA) (Mn 18,000 g/mol).

Table 3. Photokinetic analysis of decolouration of high Tg methacrylate-naphthopyran conjugates relative to the control naphthopyran 2 in host matrix.a

b c k1 k2 T1/2 e sample Mn A0 -1 A1 -1 A2 Ath d Tg (min ) (min ) (s) 2 - 1.22 0.59 0.61 0.07 0.12 0.25 144 - 7a 5,200 1.26 0.67 0.68 0.11 0.09 0.22 106 102.8 7b 12,300 1.10 0.64 0.66 0.10 0.10 0.22 116 117.8 7c 16,900 0.97 0.60 0.66 0.10 0.11 0.21 120 121.4 7d 18,400 1.07 0.58 0.64 0.09 0.13 0.22 135 121.6 7e 19,100 1.07 0.54 0.61 0.08 0.14 0.23 151 122.0 7f 24,000 0.98 0.49 0.58 0.07 0.16 0.23 180 122.0 9 12,500 1.11 0.50 0.55 0.06 0.21 0.22 189 127.1 2 - 0.90 0.61 0.61 0.07 0.11 0.25 137 - 8a 3,900 0.63 0.52 0.56 0.07 0.18 0.23 177 134.4 8b 4,300 0.49 0.48 0.54 0.07 0.20 0.23 198 135.7 8c 5,400 0.52 0.47 0.52 0.06 0.21 0.23 219 140.4 8d 10,600 0.37 0.45 0.49 0.06 0.23 0.24 252 145.0 8e 12,100 0.33 0.45 0.48 0.06 0.24 0.25 273 145.2 10 9,500 0.51 0.43 0.47 0.05 0.28 0.24 342 144.8

a Host = PEGMA:EBPDMA 1:4 mass composition, samples initially irradiated at 350-400 nm for 1000 seconds, then decolouration monitored at max of the coloured b form (500 nm) in the dark for 4800 seconds. Molecular Weight (Mn, g/mol) estimated from GPC analysis: calibration with p(MMA) standards was used for Mn evaluation of p(MMA) conjugates and PS calibration used for p(CEM) conjugates. c Measured absorbance intensity at onset of thermal decolouration period. d Time taken for the e initial absorbance value, A0, to decay to half its original value. Thermal analysis of conjugates evaluated using a Mettler Toledo DSC 821 instrument.

Overall it appears that the ability to depress the photochromic transitions (both colouration and decolouration) in the host matrix by using increasingly longer and more rigid tailing is universally applicable. Kinetic responses for a naphthopyran were

85 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

depressed fourfold across the end-functional conjugates tested (T1/2 values ranged from

70 s to 273 s). However, we have now found that the onset Mn at which this effect takes place ultimately depends on the dye. The overall speed of the dye conjugate within the host is complex and is therefore determined by many interplaying factors: the thermodynamics of the dye itself, governed by electronic substitution and steric constraints, as well as subsequent environmental effects, such as the overall rigidity of its local surroundings.

3.2.5 Concurrent Influence of Local Rigidity: Colourability Evaluation

The initial photocolouration period is marked by competitive thermal and photochemical pathways interconverting the isomers, which results in complex kinetics.56 Nonetheless, a comparison of normalised colouration curves can be insightful enough to distinguish general trends, as Figure 7. Overall it displays a general retardation trend in attainment of photosteady state, corresponding with increasing rigidity of the attached polymer. The most striking effect is shown by the difference in the overall speed of control 2 in solution vs. its behaviour in the host matrix and the beneficial role that p(EHA) conjugation can play in reinstating fast colouration speed to the dye in the matrix.

Figure 7. Normalised colouration of various end-functional conjugates and control 2 in PEGDMA: EBPDMA host matrix relative to control 2 in toluene, listed from fastest (6b) to slowest (2).

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Studies on photochromic colouration behaviour in solution57 have shown that the maximum intensity of colour (colourability, A0) that is achievable by a photochromic can be influenced by changes in the thermal reverse processes. This is because they can affect the amount of colourless form that is able to convert photochemically during the steady-state irradiation. Since our methodology has a significant influence on the thermal decolouration process, a survey of the colourability of the samples was therefore warranted. This was carried out by comparing the A0 value achieved by the end of the UV irradiation period for the end functional samples, with those of the control sample 2. Each contained the same concentration of photochromic moiety and were prepared and tested together (i.e., under the same testing conditions).

Figure 8. Measured absorbance intensity A0 at onset of thermal decolouration period of various naphthopyran end-functional conjugates (6a, 6b, 7a, 7b, 7d, 8a, 8c, 8d) with respect to the control 2, in the host matrix PEGDMA:EBPDMA (1:4) with dye concentration: 1.50 × 10-7 mol/g.

Interestingly, Figure 8 shows a general reduction in colourability with conjugates of increasing Tg. Furthermore, a notable decrease in the major thermal bleaching constant, k1, with respect to that of the control 2 was also found to be associated with this overall decrease in colourability (Figure 9). Enhanced colourability has also been separately displayed for this dye when conjugated to lubricating tails such as poly(dimethylsiloxane) and poly(ethyleneglycol), as well as for a similar naphthopyran 40 conjugated to a low Tg polymer (n-butyl acrylate). Because the photochromic molecules can experience increasing difficulty in achieving the necessary conformations for ring opening and isomerization there is the potential for colouration to be diminished in a rigid environment. Both the rate of ring 87 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______opening and the frequency of necessary configurations leading to the correct activated state can be compromised. Whether these effects are general and therefore common to other classes of photochromics is still under investigation.

Figure 9. Evolution of k1(conjugate) / k1(control) with A0 (conjugate)/A0 (control) of naphthopyran end-functional conjugates (6a, 6b, 7a, 7b, 7d, 8a, 8c, 8d) in the host matrix PEGDMA:EBPDMA (1:4) with dye concentration: 1.50 × 10-7 mol/g.

3.2.6 Copolymerized Naphthopyran versus End-functional

The location of the naphthopyran moiety in the final polymer chain is a factor that can affect the capacity of polymer conjugation to regulate photochromic kinetics. As previously mentioned, the end-functional conjugates have the naphthopyran positioned precisely at the end of each polymer chain. This approach has been greatly exploited in our laboratories because it has the benefit of controlling the exact location of the dye moiety with respect to the polymer backbone as well as the final quantity. Furthermore, it has allowed us to discriminate interplaying factors that influence the kinetics within a host matrix, such as the nature and length of the chain, the level of encapsulation, and the ability to influence the local environment. When the naphthopyran is utilized as a monomer during the polymerization process, the final conjugate consists of statistically distributed dye units pendant along the backbone. Logically, it also means that the conjugates can be synthesized to contain more than one naphthopyran unit per chain which also means the doping concentration that is required to attain comparable levels of colouration within the host matrix to the end-functional conjugates, can also be reduced. Nonetheless, using this approach one is not able to regulate the exact location

88 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

of the dye and there is no guarantee that the polymerization will completely convert all photochromic monomer units into polymer chains. In this work we have not fully explored the capacity of the copolymers to attain tuneable kinetics in the matrix through variation of chain length. Recent work has however shown that Y-branching architecture, which places the dye pendant in the middle of the chain, may be a better compromise by providing both a precise and in-chain placement of the dye.40 The naphthopyran copolymers displayed a pronounced effect on kinetics as a result changes to local rigidity. As can be seen in Figure 10, a comparison of the T1/2 values for thermal decolouration showed that each naphthopyran copolymer sample displayed a stronger effect on kinetics compared with the end-functional naphthopyran samples of comparable Mn values (in Tables 2 and 3, compare 6c with 11, 7b with 9 and 8d with

10). First, in a low Tg environment, the p(EHA)-naphthopyran copolymer 11 was faster compared with the end-functional comparison 6c, and both of the p(MMA) and p(CEM) copolymer samples, 9 and 10, were much slower compared with similar molecular weight end-functional conjugates, 7b and 8d, respectively. This suggests that within a copolymer there may be greater interaction of pendant naphthopyran moieties with other monomer units, making this system less dependent on chain coiling and partitioning around dye molecules in order to manifest a kinetic response.

Figure 10. Measured T½ values representing thermal decolouration behaviour of naphthopyran end-functional conjugates (6c, 7b, and 8d) vs. corresponding Mn naphthopyran copolymers (11, 9 and 10) in the host matrix PEGDMA:EBPDMA (1:4). Dye concentration = 1.5 × 10-7 mol/g (7b and 8d); 0.75 × 10-7 mol/g (6c, 11 and 9) and 1.0 × 10-7 mol/g (8d). pEHA = poly(2-ethylhexyl acrylate); pMMA = poly(methyl methacrylate); pCEM = poly(carbazolylethyl methacrylate

89 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

These results are preliminary, however, they exemplify that both dye-functionalized ATRP initiators and monomers can be exploited with controlled polymerization techniques to synthesize dye-polymer conjugates. Above all, both are practical strategies with beneficial aspects worth considering for controlling photochromic performance in a host matrix.

3.3 Conclusion

This work showed that polymer conjugation can be applied to naphthopyran dyes to comprehensively regulate their switching speed within a rigid host environment. By carrying out a survey on a range of conjugates of various polymer types synthesized by ATRP, broad tuning of the photochromic decolouration kinetics was achieved by modulation of local rigidity. Systematic tuning was displayed by modifying the chain length of end-functional conjugates made from a naphthopyran-functionalized ATRP initiator. A comparison of their kinetics to an unconjugated control indicated that the Mn necessary to induce a slowing effect within the host matrix depends on the dye, as exemplified by p(MMA) conjugation. Enhanced colouration was found to be a concurrent effect to an increase in speed, a trend that will be monitored further for other photochromic classes. Naphthopyran copolymer comparisons made from functionalized monomers displayed pronounced photochromic responses demonstrating a stronger influence of conjugated polymer tails on pendant naphthopyran moieties. The comprehensive examination confirmed that polymer conjugation introduced using ATRP is a practical strategy for methodically altering the kinetics of naphthopyrans within a broad range and a competitive alternative to modifying the electronic structure of the dye or their host matrix.

3.4 Experimental Details

Materials. All chemicals (reagents and solvents) were of high purity and were used as received unless otherwise stated. Methyl methacrylate (99% Aldrich) was purified by passing through aluminum oxide 90 (activated basic, 0.063 to 0.200 nm, Merck) to remove inhibitors. N-(n-Pentyl)-2-pyridylmethanimine was synthesized as described in literature.58 1-(4-Methoxy-phenyl)-1-phenylprop-2-yn-1-ol was synthesized from 4- methoxybenzophenone using a procedure described in literature.13 Methyl-1,4- dihydroxynaphthalene-2-carboxylate was directly synthesized from 1,4-dihydroxy-2- naphthoic acid using methyl iodide.59 All reagents were purchased from Aldrich

90 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Chemical unless otherwise stated. All chromatography was performed using silica gel (Kieselgel Merck 60, 0.040 to 0.063 mm), and TLC was performed on Merck Silica

60F254 plates.

General Experimental Measurements. Gel permeation chromatography (GPC) was performed on a Waters 515 HPLC pump and Waters 717 plus autosampler equipped with Waters 2414 refractive index detector and three mixed-C PLgel columns (7.5 × 300 mm2, 5 m particle size, linear molecular weight range 2002000000) and one mixed-E PLgel column (7.5 × 300 mm2, 3 m particle size, linear molecular weight range up to 30000) from Polymer Laboratories. Tetrahydrofuran (THF) with a flow rate of 1.0 mL/min was used as eluent at 22 ± 2 °C. Molecular weights for poly(2-(N- carbazolyl)ethyl methacrylate) conjugates were calculated via calibration with narrow polydispersity polystyrene standards (Polymer Laboratories) ranging from 600 to 7.5 × 6 10 g/mol. Molecular weights (Mn) of poly(2-ethylhexyl acrylate) conjugates were calculated using Mark-Houwink parameters60 on the PS calibration. The system was also calibrated with narrow poly(methyl methacrylate) standards in the range of 500 to 6 10 g/mol to derive Mn values of p(MMA) conjugates. Number (Mn) and weight-average

(Mw) molecular weights were evaluated using Waters Millennium/Empower software. A third-order polynomial was used to fit the log M versus time calibration curve, which appeared to be linear across the molecular weight ranges. 1H (400 MHz) and 13C NMR (100 MHz) spectra were obtained with a Bruker Av400 spectrometer at 25 °C. Spectra were recorded for samples dissolved in deuterated solvent, and chemical shifts are reported as parts per million from external tetramethylsilane. Monomer conversions were obtained from the 1H NMR spectra. The resonances integrated to obtain conversions for EHA polymerizations were the vinyl peaks at 5.8 and 6.4 ppm (monomer only) and the OCH2- peaks at 3.9 to 4.1 ppm (monomer and polymer). The resonances integrated to obtain conversions for MMA polymerizations were the vinyl peaks at 5.6 and 6.1 ppm (monomer only) and the OCH3 peaks at 3.6 to 3.7 ppm (monomer and polymer). For CEM polymerizations, the integrated resonances were the vinyl peaks at 5.8 and 5.9 ppm (monomer) and the aromatic carbazole region (ArH, 2H) between 7.8 and 8.2 ppm (monomer and polymer). The compositional ratio of the copolymers was calculated by IH NMR via the integrated peak intensity ratio of naphthopyran versus polymer. All other spectra were recorded on a Bruker Av400 spectrometer. 2D NMR standard gradient DQF-COSY, HSQC, and

91 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

HMBC experiments were acquired for resonance assignment purposes of naphthopyran derivatives 1-5. Positive ion EI mass spectra were run on a ThermoQuest MAT95XL mass spectrometer using ionization energy of 70 eV. Accurate mass measurements were obtained with a resolution of 500010000 using PFK as the reference compound. Thermal analysis by differential scanning calorimetry (DSC) was performed to determine the Tg of the conjugates. This was carried out using a Mettler Toledo DSC821 machine with temperature and heat flow calibrated using indium and zinc as reference substances. Samples ( 10 mg) were heated under nitrogen from 0 to 160 °C at 10

°C/min to remove the thermal history and then from 0 to 200 °C at 10 °C/min. The Tg values were taken from the midpoints of the heat flow changes from the second heat cycle.

Photochromic Analysis. Under continuous UV irradiation, the photochromic responses of samples were analyzed on a light table composed of a Cary 50 spectrophotometer to measure absorbance values with time and a 160 W Oriel xenon lamp as an incident light source. A series of two filters (Edmund Optics 320 cut-off and bandpass filter U-340) were used to restrict the output of the lamp to a narrow band (350-400 nm). The samples were maintained at 20 °C and monitored at the maximum absorbance of the coloured form for a period of 1000 s. Then, the thermal decolouration was monitored in the absence of UV irradiation for an additional 4800 s. Sample 2 was also measured in toluene (105 M) using a quartz cell of 1 cm path length.

Figure 11. Numbering system used for naphthoyran compounds 1-5

92 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

Synthesis of methyl 6-hydroxy-2-(4-methoxyphenyl)-2-phenyl-2H-naphtho[1,2- b]pyran-5-carboxylate (4).46 A mixture of 1-(4-methoxy-phenyl)-1-phenylprop-2-yn- 1-ol (3.3 g, 13.7 mmol), methyl 1,4-dihydroxynapthalene-2-carboxylate (3.0 g, 13.7 mmol), p-toluenesulfonic acid monohydrate (0.24 g, 1.38 mmol), and silica gel 60 (5.8 g) was ground for 10 min at room temperature using a mortar and pestle, and the mixture was then left to stand for 1 h. The reaction mixture was then passed through a short silica filtration column with toluene to remove a large portion of darkened baseline material. The bright orange filtrate was concentrated in vacuo to give a gummy orange material that was then purified by column chromatography on silica gel using toluene as the eluent. The solvent was evaporated in vacuo, and the resulting orange oil was treated with a small amount of diethyl ether/hexane. The product crystallized from 1 solution, giving a bright yellow solid. (4.3 g, 71 % yield). H NMR (400 MHz, d6- acetone) : 3.72 (s, 3H, ArOCH3), 4.04 (s, 3H, COOCH3), 6.37 (d, J 9.88 Hz, 1H, H-3), 6.84 (apparent d, J = 8.78 Hz, 2H, H-3), 7.22 - 7.25 (m, 1H, H-4), 7.31 - 7.34 (m, 2H, H-3), 7.47 (apparent doublet, J = 8.78 Hz, 2H, H-2), 7.51 (d, J = 9.88 Hz, 1H, H-4), 7.56 - 7.61 (m, 3H, H-2 and H-9), 7.73 - 7.77 (m, 1H, H-8), 8.32 (d, J = 8.42 Hz, 1H, 13 H-10), 8.42 (d, J = 8.42 Hz, 1H, H-7), 12.19 (s, 1H, OH) ppm. C NMR (100 MHz, d6- acetone) : 53.1 (COOCH3), 55.5 (ArOCH3), 81.9 (C-2), 103.3 (C-5), 114.3 (C-3), 114.6 (C-4a), 122.8 (C-7), 124.5 (C-4), 124.8 (C-10), 126.0 (C-10a), 127.3 (C-2), 127.7 (C-9), 128.2 (C-4), 128.8 (C-3), 128.9 (C-2), 129.0 (C-3), 129.5 (C-6a), 130.9 (C-8),

137.6 (C-2a), 141.9 (C-1a), 146.2 (C-2b), 157.2 (C-6), 160.1 (C-4), 173.0 (COOCH3) ppm. Refer to Figure 11 for numbering system used for NMR assignments of compound 1. MS (EI) m/z: 438.1 ([M]+ 28%), 405.1 (19), 375.1 (16), 361.1 (13), 298.0 (12), 289.1

(14), 276.1 (12), 203.1 (13). MS (HR, EI) m/z: 438.1456 (C28H22O5 requires 438.1462).

Synthesis of methyl 6-(isobutyryloxy)-2-(4-methoxy-phenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (2). To an ice-cooled solution of methyl 6- hydroxy-2-(4-methoxyphenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate, were added 1 (0.18 g, 0.41 mmol) and triethylamine (TEA) (0.14 mL, 1.0 mmol) in dry dichloromethane (CH2Cl2) (7 mL) dropwise and isobutyryl chloride (0.09 mL, 0.86 mmol) under argon. The solution was stirred with cooling for 0.5 h and was then left to be stirred for an additional 12 h at room temperature. The solvent was evaporated in vacuo, and the residue was redissolved in diethyl ether (Et2O) (30 mL) and washed successively with 0.5 M HCl, water, aqueous NaHCO3, water, and brine. The organic

93 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

layer was dried with MgSO4, and the solvent was evaporated in vacuo. The crude product was purified by column chromatography (silica gel 60, CH2Cl2), giving the 1 product as pale tan-coloured crystals (160 mg, 77 %). H NMR (400 MHz, d6-acetone) : 1.35 (d, J = 6.95 Hz, 6H, H-13a and H-13b), 2.90 (sept, J = 6.95 Hz, 1H, H-12), 3.73

(s, 3H, ArOCH3), 3.91 (s, 3H, COOCH3), 6.46 (d, J = 9.88 Hz, 1H, H-3), 6.87 (apparent d, J = 8.78 Hz, 2H, H-3), 6.96 (d, J = 9.88 Hz, 1H, H-4), 7.24 - 7.28 (m, 1H, H-4), 7.337.37 (m, 2H, H-3), 7.46 (apparent doublet, J = 8.78 Hz, 2H, H-2), 7.55 - 7.62 (m, 3H, H-2 and H-9), 7.65 - 7.69 (m, 1H, H-8), 7.80 (d, J = 8.42 Hz, 1H, H-10), 8.44 13 (d, J = 8.42 Hz, 1H, H-7) ppm. C NMR (100 MHz, d6-acetone) : 19.4 (C-13a and

13b), 34.7 (C-12), 52.9 (COOCH3), 55.6 (ArOCH3), 83.7 (C-2), 114.3 (C-4a), 114.5 (C- 3), 121.2 (C-5), 121.9 (C-4), 123.1 (C-7), 123.3 (C-10), 127.1 (C-6a), 127.4 (C-2), 128.3 (C-10a), 128.5 (C-4), 128.8 (C-9), 128.9 (C-8), 129.0 (C-2), 129.2 (C-3), 130.1 (C-3), 137.4 (C-2a), 140.1 (C-6), 145.9 (C-2b), 146.7 (C-1a), 160.3 (C-4), 166.4

(COOCH3), 175.5 (C-11) ppm. Refer to Figure 11 for numbering system used for NMR assignments of compound 2. MS (EI) m/z: 508.2 ([M]+ 28%), 437.1 (18), 405.1 (31),

377.1 (31), 361.1 (10). MS (HR, EI) m/z: 508.1881 (C32H28O6 requires 508.1880).

Synthesis of methyl 6-(2-bromo-2-methylpropanoyloxy)-2-(4-methoxy-phenyl)-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (3). This compound was synthesized from 1 and 2-bromo-isobutyrylbromide using the same general procedure as above and isolated as a peach-coloured glassy solid (520 mg, 78 %) after purification by column 1 chromatography (silica gel 60, CH2Cl2) and recrystallization from diethyl ether. H

NMR (400 MHz, d6-acetone) : 2.13 (6H, s, H-13a and H-13b), 3.74 (s, 3H, ArOCH3),

3.94 (s, 3H, COOCH3), 6.48 (d, J = 9.88 Hz, 1H, H-3), 6.88 (apparent d, J = 8.78 Hz, 2H, H-3), 6.97 (d, J = 9.88 Hz, 1H, H-4), 7.25 - 7.29 (m, 1H, H-4), 7.34 - 7.38 (m, 2H, H-3), 7.46 (apparent d, J = 8.78 Hz, 2H, H-2), 7.55 - 7.57 (m, 2H, H-2), 7.65 - 7.70 (m, 2H, H-8, H-9), 8.02 (d, J = 8.42 Hz, 1H, H-10), 8.47 (d, J = 8.42 Hz, 1H, H-7) ppm. 13 C NMR (100 MHz, d6-acetone) : 31.2 (C-12), 53.3 (COOCH3), 55.6 (ArOCH3), 56.7 (C-12), 83.8 (C-2), 114.3 (C-3), 114.5 (C-4a), 121.1 (C-5), 121.8 (C-4), 122.9 (C-10), 123.2 (C-7), 127.1 (C-6a), 127.4 (C-2), 128.1 (C-10a), 128.5 (C-4), 129.1 (C-9), 129.1 (C-8), 129.1 (C-2), 129.2n(C-3), 130.3 (C-3), 137.3 (C-2a), 139.5 (C-6), 145.9 (C-2b),

147.2 (C-1a), 160.3 (C-4), 166.2 (COOCH3), 170.5 (C-11) ppm. Refer to Figure 11 for numbering system used for NMR assignments of compound 3. MS (EI) m/z: 586.1

94 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

([M]+ 17%), 506 (10), 475.1 (20), 437.1 (29), 405 (100), 377.1 (63), 289.1 (15), 121.0

(11), 69.1(11). MS (HR, EI) m/z: 586.0987 (C32H27BrO6 requires 586.0986).

Syntheis of methyl 6-(methacryloyloxy)-2-(4-methoxy-phenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (4). This compound was synthesized from 1 and methacryloyl chloride using the same general procedure as that above and was isolated as a cream-coloured solid after purification by column chromatography (silica gel 60, 1 1:1 Et2O/Hexane) (480 mg, 86%). H NMR (400 MHz, d6-acetone) : 2.09 (s, 3H, H-

14), 3.73 (s, 3H, ArOCH3), 3.86 (s, 3H, COOCH3), 5.91 - 5.92 (m, 1H, H-13a), 6.39 (broad s, 1H, H-13b), 6.46 (d, J = 9.88 Hz, 1H, H-3), 6.88 (apparent d, J = 8.78 Hz, 2H, H-3), 7.01 (d, J = 9.88 Hz, 1H, H-4), 7.25 - 7.28 (m, 1H, H-4), 7.34 - 7.37 (m, 2H, H- 3), 7.47 (apparent d, J = 8.78 Hz, 2H, H-2), 7.56 - 7.62 (m, 3H, H-2 and H-9), 7.66 - 7.70 (m, 1H, H-8), 7.81 (d, J = 8.42 Hz, 1H, H-10), 8.46 (d, J = 8.42 Hz, 1H, H-7) ppm. 13 C NMR (100 MHz, d6-acetone) : 18.6 (C-14), 52.9 (COOCH3), 55.6 (ArOCH3), 83.7 (C-2), 114.2 (C-4a), 114.5 (C-3), 120.9 (C-5), 121.9 (C-4), 123.1 (C-7), 123.5 (C-10), 127.1 (C-6a), 127.4 (C-2), 128.2 (C-13), 128.3 (C-10a), 128.5 (C-4), 128.8 (C-9), 128.9 (C-8), 129.0 (C-2), 129.2 (C-3), 130.2 (C-3), 136.5 (C-12), 137.4 (C-2a), 140.6

(C-6), 145.9 (C-2b), 146.8 (C-1a), 160.3 (C-4), 166.1 (C-11), 166.3 (COOCH3) ppm. Refer to Figure 11 for numbering system used for NMR assignments of compound 4. MS (EI) m/z: 506.2 ([M]+ 33%), 474.1 (11), 437.1 (38), 405.1 (100), 377.1 (54), 69.2

(13). MS (HR, EI) m/z: 506.1723 (C32H26O6 requires 506.1724).

Synthesis of methyl 6-(acryloyloxy)-2-(4-methoxy-phenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (5). This compound was synthesized from 1 and acryloyl chloride using the same procedure as above and was isolated as a cream- coloured solid after purification by column chromatography (silica gel 60, 1:1 1 Et2O/Hexane) (250 mg, 86%). H NMR (400 MHz, d6-acetone) : 3.73 (s, 3H,

ArOCH3), 3.86 (s, 3H, COOCH3), 6.18 (dd, J = 10.24 Hz, J = 1.46 Hz, 1H, H-13b), 6.46 (d, J = 9.88 Hz, 1H, H-3), 6.51 (d, J = 10.24 Hz, 1H, H-12), 6.63 (dd, J = 17.20 Hz, J = 1.46 Hz, 1H, H-13a), 6.88 (apparent d, J = 8.78 Hz, 2H, H-3), 7.01 (d, J = 9.88 Hz, 1H, H-4), 7.25 - 7.28 (m, 1H, H-4), 7.34 -.37 (m, 2H, H-3), 7.47 (apparent doublet, J = 8.78 Hz, 2H, H-2), 7.56 - 7.62 (m, 3H, H-2 and H-9), 7.66 - 7.70 (m, 1H, H-8), 7.81 (d, J = 8.42 Hz, 1H, H-10), 8.46 (d, J = 8.42 Hz, 1H, H-7) ppm. 13C NMR (100

MHz, d6-acetone) : 52.9 (COOCH3), 55.6 (ArOCH3), 83.7 (C-2), 114.4 (C-4a), 114.5 (C-3), 120.9 (C-5), 121.9 (C-4), 123.2 (C-7), 123.5 (C-10), 127.1 (C-6a), 127.4 (C-2),

95 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

128.2 (C-12), 128.3 (C-10a), 128.5 (C-4), 128.9 (C-9), 129.0 (C-8), 129.1 (C-2), 129.2 (C-3), 130.2 (C-3), 133.9 (C-13), 137.5 (C-2a), 140.2 (C-6), 146.0 (C-2b), 146.9 (C-

1a), 160.3 (C-4), 164.9 (C-11), 166.2 (COOCH3) ppm. Refer to Figure 11 for numbering system used for NMR assignments of compound 5. MS (EI) m/z: 492.1 ([M]+ 34%), 460.1 (15), 437.1 (30), 405.1 (100), 377.1 (71), 334.1 (12), 318.1 (10),

305.1 (10), 289 (13), 55 (12). MS (HR, EI) m/z: 492.1569 (C31H24O6 requires 492.1573).

Synthesis of 2-(9H-carbazol-9-yl) ethyl methacrylate (CEM). A solution of methacryloyl chloride (distilled, 3.50 mL, 35.6 mmol) was slowly added via a gastight syringe to a solution of triethylamine (4.95 mL, 35.6 mmol) and 2-(9H-carbazol-9- yl)ethanol (5 g, 23.7 mmol) in dry THF (200 mL). The mixture was kept under an inert atmosphere of argon and cooled to 0 °C during the addition and was then left to be stirred for an additional 12 h at room temperature. The solvent was evaporated in vacuo and then redissolved in CH2Cl2 (150 mL) and washed successively with water (2 × 100 mL) and saturated brine. The organic layer was dried with MgSO4, and the solvent was evaporated under vacuum. The product was then purified by recrystallization with ethanol/chloroform (2:1) and isolated as a fluffy white solid (3.4 g, 52 %). 1H NMR

(400 MHz, CDCl3) : 1.81 (s, 3H, CH3), 4.54 (t, J = 5.8 Hz, 2H, CH2), 4.63 (t, J = 5.8

Hz, 2H, CH2), 5.49 (s, 1H, C=CH), 5.94 (s, 1H, C=CH), 7.24 - 7.28 (m, 2H, ArH), 7.44 13 - 7.48 (m, 4H, ArH), 8.11 (d, J = 7.68 Hz, ArH) ppm. C NMR (100 MHz, CDCl3) : 18.2, 41.6, 62.5, 108.6, 119.2, 120.4, 123.0, 125.8, 126.3, 135.7, 140.4, 167.3 ppm. MS (EI) m/z: 279.1 ([M]+ 35%), 193.1 (31), 180.1 (100), 152.0 (12), 69 (14). MS (HR, EI) m/z: 279.1258 (C18H17O2N requires 279.1254).

ATRP of 2-ethylhexylacrylate with naphthopyran initiator 3. A 25 mL stock solution containing 2-ethylhexyl acrylate (22.10 g, 119.9 × 103 mol, 4 M), naphthopyran initiator 3 (469.6 mg, 8 × 104 mol), and dNbpy ligand (653.4 mg, 16.0 × 104 mol) was prepared. To ampoules containing CuBr (18.3 mg, 1.28 × 104 mol) were added 4 mL aliquots, and the final ratio of [2-EHA]:[3]:[dNbpy ligand]:[CuBr] was 150:1:2:1. The ampoules were then degassed with three freeze-evacuate-thaw cycles, sealed, and then heated to 90 °C in a thermostatted oil bath; the polymerization was monitored for 1-7 h. End-functional naphthopyran conjugates 6b and 6c were obtained from 1 and 2 h polymerization intervals, respectively. Napthopyran conjugate 6a was obtained in the same manner by preparing a 5 mL stock solution containing 2-

96 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

ethylhexyl acrylate (4.42 g, 24.0 × 103 mol), naphthopyran initiator 3 (140.9 mg, 2.40 × 104 mol), and dNbpy ligand (196 mg, 4.80 × 104 mol). A 4 mL aliquot was added to an ampoule containing CuBr (27.5 mg, 1.92 × 104 mol) so that the final ratio of [2- EHA]:[3]:[dNbpy ligand]:[CuBr] was 100:1:2:1. The ampoules were then degassed with three freeze-evacuate-thaw cycles, sealed, and then heated to 90 °C in a thermostatted oil bath for 1 h. The final polymers were purified by column chromatography (silica gel 60, 1:1 CH2Cl2/Et2O), followed by two separations carried out by dissolving the polymer in hexane and sequentially washing with methanol to remove the residual monomer.

ATRP of methyl methacrylate with naphthopyran initiator 3. A 20 mL stock solution of methyl methacrylate (6.84 g, 6.84 × 102 mol, 3.42 M), naphthopyran initiator 3 (201 mg, 3.42 × 104 mol) and N-PPMA ligand (120 mg, 6.84 × 104 mol) in toluene was prepared. To ampoules containing CuBr (7.4 mg, 5.13 × 105 mol) were added 3 mL aliquots so that the final ratio of [MMA]:[3]:[ligand]:[CuBr] was 200:1:2:1. The ampoules were then degassed with three freeze-evacuate-thaw cycles, sealed, and then heated to 90 °C in a thermostatted oil bath for 2-16 h to obtain end-functional napthopyran conjugates 7a-7f. The final polymers were individually purified by two precipitations by dissolution of the crude residues in a minimal volume of CH2Cl2, followed by drop-wise addition to excess methanol.

ATRP of CEM with naphthopyran initiator 3. A 10 mL stock solution of 2-(9H- carbazol-9-yl)ethyl methacrylate (2.0 g, 7.16 × 103 mol), naphthopyran initiator 3 (42.1 mg, 7.16 × 105 mol), and N-PPMA ligand (25.2 mg, 1.43 × 104 mol) in toluene was prepared. To ampoules containing CuBr (2.05 mg, 1.43 × 105 mol) were added 2 mL aliquots so that the final ratio of [CEM]:[3]:[ligand]:[CuBr] was 100:1:2:1. The ampoules were then degassed with three freeze-evacuate-thaw cycles, sealed, and then heated to 90 °C in a thermostatted oil bath; the polymerization was monitored for 3-6 h. End-functional napthopyran conjugates 8a-8c were obtained from 3-5 h polymerization intervals. Napthopyran conjugates 8d and 8e were obtained by preparing a 5 mL stock solution containing 2-(9H-carbazol-9-yl)ethyl methacrylate (1.0 g, 3.58 × 103 mol), naphthopyran initiator 3 (21.0 mg, 3.58 × 105 mol), and PMDETA ligand (6.20 mg, 3.58 × 105 mol) in toluene. To two ampoules containing CuBr (2.05 mg, 1.43 × 105 mol) were added individually 2 mL aliquots so that the final molar ratio of [CEM]:[3]:[ligand]:[CuBr] was 100:1:1:1. The two ampoules were then degassed with

97 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______three freeze-evacuate-thaw cycles, sealed, and then individually heated to 90 °C in a thermostatted oil bath for 90 min and 3 h. The final polymers were individually purified by several precipitations by dissolution of the crude residues in a minimal volume of

CH2Cl2, followed by drop-wise addition to excess methanol.

ATRP synthesis of p(MMA)-co-p(chromene), copolymer 9. MMA (900 mg, 8.99 × 103 mol), naphthopyran methacrylate 4 (100 mg, 1.97 × 104 mol), ethyl-2-bromo isobutyrate initiator (8.96 mg, 4.59 × 105 mol), and N-PPMA ligand (16.2 mg, 9.18 × 105 mol) were dissolved in 2.6 mL of toluene. The solution was then transferred to an ampoule containing CuBr (6.59 mg, 4.59 × 105 mol) so that the final ratio of [monomers]:[initiator]:[ligand]:[CuBr] was 200:1:2:1. The ampoule was then degassed with three freeze-evacuate-thaw cycles, sealed, and then heated to 90 °C in a thermostatted oil bath for 16 h. The polymer was then purified by two precipitations by dissolution of the crude residues in a minimal volume of CH2Cl2, followed by drop-wise addition to excess methanol.

ATRP Synthesis of p(CEM)-co-p(chromene), copolymer 10. A 10 mL stock solution of ethyl-2-bromo isobutyrate initiator (14.40 mg, 7.38 × 105 mol) and PMDETA ligand (12.79 mg, 7.38 × 105 mol) in toluene was prepared. A 1 mL aliquot was added to CEM (194 mg, 6.95 × 104 mol) and naphthopyran methacrylate 4 (21.6 mg, 4.26 × 105 mol), and this solution was then transferred to an ampoule containing CuBr (1.06 mg, 7.38 × 106 mol) so that the final ratio of [monomers]:[initiator]:[ligand]:[CuBr] was 100:1:1:1. The ampoule was then degassed with three freeze-evacuate-thaw cycles, sealed, and then heated to 90 °C in a thermostatted oil bath for 2 h. The polymer was then purified by several precipitations by dissolution of the crude residues in a minimal volume of CH2Cl2, followed by drop-wise addition to excess methanol.

ATRP synthesis of p(EHA)-co-p(chromene), copolymer 11. EHA (2.38 g, 12.9 × 103 mol), naphthopyran acrylate 5 (196 mg, 3.98 × 104 mol), ethyl-2-bromo isobutyrate initiator (26.0 mg, 1.33 × 104 mol), and dNbpy ligand (108 mg, 2.66 × 104 mol) were dissolved in 1 mL of toluene. The solution was then transferred to an ampoule containing CuBr (19.10 mg, 1.3 × 104 mol) so that the final ratio of [monomers]:[initiator]:[ligand]:[CuBr] was 100:1:2:1. The ampoule was then degassed with three freeze-evacuate-thaw cycles, sealed, and then heated to 90 °C in a thermostatted oil bath for 9.5 h. The polymer was then purified by column

98 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

chromatography (silica gel 60, 1:1 CH2Cl2/Et2O), followed by two separations carried out by dissolving the polymer in hexane and sequentially washing with methanol to remove the residual monomer.

Preparation of Photochromic Test Samples. Polymer photochromic conjugates were individually dissolved in a industrial lens formulation made up of 1:4 weight ratio of poly(ethylene glycol) (400) dimethacrylate and 2,2-bis((4-methacryloxy ethoxy)phenyl)propane (specific monomer structures given below) with 0.4% AIBN.

The samples were then cured at 80 °C for 16 h in a standard mould to give optically clear test samples of equivalent thickness (~ 2.6 mm). End-functional naphthopyran conjugates (6a-6c, 7a-7f, and 8a-8e) and naphthopyran control 2 were doped at equivalent concentrations of 1.5 × 107 mol/g of lens formulation. Copolymer conjugates 9 and 11 were doped at a concentration of 0.75 × 107 mol/g of lens formulation, and p(CEM) copolymer conjugate 10 was doped at a concentration of 1.0 × 107 mol/g to compensate for different naphthopyran contents. The final concentrations were chosen to maintain optical densities in a meaningful range for the detector.

3.5 References

(1). Dürr, H. General Introduction. In Photochromism: Molecules and Systems, 1st ed.; Dürr H., Bouas-Laurent, H., Eds.; Studies in Organic Chemistry Series 40; Elsevier: Amsterdam, 1990; Vol. 40, pp 1-14. (2). Organic Photochromic and Thermochromic Compounds; Crano, J. C., Guglielmetti, R. J., Eds.; Plenum Press: New York, 1999; Vols. 1 and 2. (3). Kawata, S.; Kawata, Y. Chem. Rev. 2000, 100, 1777-1788. (4). Berkovic, G.; Krongauz, V.; Weiss, V. Chem. Rev. 2000, 100, 1741-1753. (5). Evans, R. A.; Such, G. K. Aust. J. Chem. 2005, 58, 825-830. (6). Mendintz, I. L.; Trammell, S. A.; Mattoussi, H.; Mauro, M. J. Am. Chem. Soc. 2004, 126, 30-31.

99 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

(7). Zhu, L.; Zhu, M.-Q.; Hurst, J. K.; Li, A. D. Q. J. Am. Chem. Soc. 2005, 127, 8968-8970. (8). Zhu, M.-Q.; Zhu, L.; Han, J. J.; Wu, W.; Hurst, J. K.; Li, A. D. Q. J. Am. Chem. Soc. 2006, 128, 4303-4309. (9). Zhu, L.; Wu, W.; Zhu, M.-Q.; Han, J. J.; Hurst, J. K.; Li, A. D. Q. J. Am. Chem. Soc. 2007, 129, 3524-3526. (10). Lee, H. i.; Wu, W.; Oh, J. K.; Mueller, L.; Sherwood, G.; Peteanu, L.; Kowalewski, T.; Matyjaszewski, K. Angew. Chem., Int. Ed. 2007, 46, 2453–2457. (11). Van Gembert, B. Benzo and Naphthopyrans (Chromenes), Chapter 3. In Organic Photochromic and Thermochromic Compounds; Crano, J., Guglielmetti, R., Eds.; Plenum Press: New York, 1998; Vol. 1. (12). Becker, R. S.; Michi, J. J. Am. Chem. Soc. 1966, 88, 5931-5933. (13). Gabbutt, C. D.; Heron, M. B.; Instone, A. C.; Thomas, D. A.; Partington, S. M.; Husthouse, M. B.; Gelbrich, T. Eur. J. Org. Chem. 2003, 1220-1230. (14). Ottavi, G.; Favaro, G.; Malatesta, V. J. Photochem. Photobiol., A 1998, 115, 123- 128. (15). Delbaere, S.; Micheau, J.-C.; Vermeersch, G. J. Org. Chem. 2003, 68, 8968-8973. (16) Delbaere, S.; Luccioni-Huoze, B.; Bochu, C.; Teral, Y.; Campredon, M.; Vermeersch, G. J. Chem. Soc., Perkin Trans. 2. 1998, 1153-1157. (17). Hobley, J.; Malatesta, V.; Hatanaka, K.; Kajimoto, S.; Williams, S.; Fukumura, H. Phys. Chem. Chem. Phys. 2002, 4, 180-184. (18). Heron, B. M.; Gabbut, C. D.; Hepworth, J. D.; Partington, S. M.; Clarke, D. A.; Corns; S. N. Rapid Fading Photo-Responsive Materials. WO/2001/012619 A1, 2001. (19). Van Gemert, B. Photochromic Indeno-Fused Naphthopyran Compounds. U.S. Patent 5,645,767, 1997. (20) Rickwood, M.; Smith, K. E.; Gabbut, C. D.; Hepworth, J. D. Photochromic Napthopyran Compounds. U.S. Patent 5,623,005, 1997. (21). Momoda, J.; Komuro, Y. Chromene Compounds. U.S. Patent 6,469,076, 2002. (22). Manfred, M.; Herbert, Z. Diaryl-2H-naphthopyrans. U.S. Patent 6,036,890, 2000. (23). Kumar, A.; Gemert, B. V.; Knowles, D. B. Substituted Naphthopyrans. U.S. Patent 5,458,814, 1995. (24). Heller, H. G. Photochromic Chromene Compounds. U.S. Patent 5,200,116, 1993.

100 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

(25). Gemert, B. V.; Bergomi, M. P. Photochromic Naphthopyran Compounds. U.S. Patent 5,066,818, 1991. (26). Pozzo, J.-L.; Lokshin, V.; Samat, A.; Guglielmetti, R.; Dubest, R.; Aubarb, J. J. Photochem. Photobiol., A 1998, 114, 185-191. (27). Krongauz, V. Environmental Effects on Organic Photochromic Systems. In Photochromism: Molecules and Systems, 1st ed.; Dürr, H., Bouas-Laurent, H., Eds.; Studies in Organic Chemistry Series 40; Elsevier: Amsterdam, 1990; Vol. 40, p 793-820. (28). Lyubimov, A. V.; Zaichenko, N. L.; Marevtsev, V. S. J. Photochem. Photobiol., A 1999, 120, 55-62. (29). Ichimura, K. Photochromic Polymers. In Organic Photochromic and Thermochromic Compounds; Crano, J. C., Guglielmetti, R. J., Eds.; Plenum Press: New York, 1999; Vol. 2. (30). Matyjaszewski, K.; Xia, J. Chem. Rev. 2001, 101, 2921-2990. (31). Moad, G.; Rizzardo, E.; Thang, S. Aust. J. Chem. 2006, 59, 669-692. (32). Moad, G.; Rizzardo, E.; Thang, S. Aust. J. Chem. 2005, 58, 379-410. (33). Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Davis, T. P.; Such, G. K.; Yee, L. H.; Ball, G. E.; Lewis, D. A. Nat. Mater. 2005, 4, 249-254. (34). Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Yee, L. H.; Lewis, D. A. Photochromic Compositions and Light Transmissible Articles. WO 2004/041961 A1, 2003. (35). Such, G.; Evans, R. A.; Yee, L. H.; Davis, T. P. J. Macromol. Sci., Polym. Rev. 2003, C43, 547-579. (36). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2004, 37, 9664-9666. (37). Such, G. K.; Evans, R. A.; Davis, T. P. Mol. Cryst. Liq. Cryst. 2005, 430, 273- 279. (38). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2006, 39, 1392-1396. (39). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2006, 39, 9562-9570. (40). Malic, N.; Campbell, J. A.; Evans, R. A. Macromolecules 2008, 41, 1206-1214 (41). Sriprom, W.; Ne´el, M.; Gabbutt, C. D.; Heron, M.; Perrier, S. J. Mater. Chem. 2007, 17, 1885-1893. (42). Evans, R. A.; Such, G. K.; Malic, N.; Davis, T. P.; Lewis, D. A.; Campbell, J. A. Photochromic Compounds Comprising Polymeric Substituents and Methods for Preparation and Use Thereof. WO/2006/024099, 2006.

101 Chapter 3. Comprehensive Modulation of Naphthopyran Photochromism… ______

(43). Gabbutt, C. D.; Hepworth, J. D.; Heron, M.; Thomas, D. A.; Parlington, S. M. Heterocycles 2004, 63, 567-582. (44). Gabbutt, C. D.; Heron, B. M.; Instone, A. C.; Horton, P. N.; Hursthouse, M. B. Tetrahedron 2005, 61, 463-471. (45). Chamontin, K.; Lokshin, V.; Rossolin, V.; Samat, A.; Guglielmetti, R. Tetrahedron 1999, 55, 5821-5830. (46). Tanaka, K.; Aoki, H.; Hosomi, H.; Ohba, S. Org. Lett. 2000, 2, 2133-2134. (47). DiNunzio, M. R.; Gentili, P. L.; Romani, A.; Favaro, G. ChemPhysChem 2008, 9, 768-775. (48). Jockusch, S.; Turro, N.; Blackburn, F. J. Phys. Chem. A. 2002, 106, 9236-9241. (49). Kumar, A.; Van Gemert, B.; Knowels, D. Novel Substituted Naphthopyrans, WO/1995/16215, 1995. (50). Haddleton, D. M.; Jasieczek, C. B.; Hannon, M. J.; Shooter, A. J. Macromolecules 1997, 30, 2190-2193. (51). Biteau, J.; Chaput, F.; Boilot, J. J. Phys. Chem. 1996, 100, 9024-9031. (52). Zayat, M.; Levy, D. J. Mater. Chem. 2003, 13, 727-730. (53). Pozzo, J. L.; Samat, A.; Guglielmetti, R.; De Keukeleireb, D. J. Chem. Soc., Perkin Trans. 2 1993, 1327-1332. (54). Pozzo, J. L.; Samat, A.; Guglielmetti, R.; Dubest, R.; Aubard, J. Helv. Chim. Acta 1997, 80, 725-738. (55). Babazadeh, M. J. App. Polym. Sci. 2006, 102, 4989-4995. (56). Gauglitz, G. Ch. 2, Photophysical, Photochemical, and Photokinetic Properties of Photochromic Systems. In Photochromism: Molecules and Systems, 1st ed.; Dürr, H., Bouas-Laurent, H., Eds.; Elsevier: Amsterdam, 2003; pp 15-61. (57). Favaro, G.; Malatesta, V.; Mazzucato, U.; Ottavi, G.; Romani, A. J. Photochem. Photobiol., A 1995, 87, 235-241. (58). Haddleton, D. M.; Kukulj, D.; Duncalf, D. J.; Heming, A. M.; Shooter, A. J. Macromolecules 1998, 31, 5201-5205. (59). Sallenave, X.; Delbaere, S.; Vermeersch, G.; Saleh, A.; Pozzo, J.-L. Tetrahedron Lett. 2005, 46, 3257-3259. (60). Beuermann, S., Jr.; Mc Minn, J. H.; Hutchinson, R. A. Macromolecules 1996, 29, 4206-4215.

102 4 Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix.

4.1 Introduction

Practical application in ophthalmic eyewear requires photochromic compounds to be incorporated into a polymer host/substrate using one of several strategies: the process of imbibing integrates the molecules within the top layers of the host1; casting in can be carried out by dissolution or dispersion of the dyes into the host monomers prior to curing the material; or a separate layer of the dyes can be incorporated as a film on top of, in between, or in adjacent layers of the host.2 In the previous chapter I showed that photochromic switching speed can be controlled in a rigid host using engineered photochromic-polymer conjugates.3 This approach was developed using a cast-in method, where an optimized host matrix is left unmodified in order to bring about changes to photochromic performance. Instead, the dye that is added to the host matrix composition has a polymer/oligomer bound directly to it in order to bring about critical changes to its local environment, i.e., what immediately surrounds the dye within the host matrix.4,5 A local fluid environment can be introduced around the dye by conjugation to a soft oligomer, such as poly(n-butyl acrylate), p(BA), allowing greater freedom of movement during molecular rotation and resulting in faster switching.6 Specialized dye-polymer conjugates can be constructed using controlled radical polymerization techniques, such as atom transfer radical polymerization (ATRP). This is mainly carried out with the approach of growing well-defined polymers (with controlled molecular weights, Mn, and polydispersity indexes, PDI) from photochromic inititiators.7 An important feature of the technology is that tuning of the fade speed of the photochromic material can be achieved by adjusting both the Tg of the polymer and the chain length of the tail.3,7,8 It has recently been demonstrated that the geometry of the conjugate can also affect performance. Larger and more tuneable improvements have been observed for the mid- placement of the dye within p(BA), a low-Tg polymer, vs. the end placement of a dye.9,10 The Y-branching approach was developed using an aromatic central scaffold which allows the dye to be attached centrally, and then initiator sights located on opposite sides of the aromatic ring allow the radial growth of two polymer arms. Chain Chapter 4. The Importance of Macromolecular Architecture… ______

architecture therefore has an important role in determining the level of encapsulation that can be provided by polymer conjugation and its ability to affect the local environment around the photochromic. In the present chapter I extend this concept by comparing several motifs for applying p(BA) conjugation to a naphthopyran photochromic, as depicted in Figure 2.

Figure 2. Photochromic dye-p(BA) conjugate strategies: (A) end-placement of the dye; (B and C) mid-placement of the dye; (D) random copolymer and (E) gradient copolymer with pendant photochromic groups made with photochromic acrylate and methacrylate respectively. End-functional photochromic polymer conjugates (A) were assembled using a monofunctional photochromic initiator. Mid-functional photochromic-polymer conjugates (B) and (C) were explored using di-functional photochromic initiators. In the case of (B) this was approached using a symmetrical, di-functional initiator which incorporated an aliphatic scaffold, and with (C), two arms were grown biradially from opposite sides of a central photochromic molecule. Photochromic functional monomers were used for the synthesis of random copolymers (D) and gradient copolymer (E), containing pendant dye moieties. ATRP was used to polymerize these structures. Their photochromic performances were then evaluated with reference to one another and to those of unconjugated controls when cast within a rigid host matrix. Lastly, given the promising results obtained for Y-branching approaches (B) and (E), these p(BA) structures were extended to make ABA-type triblock copolymers with isobornyl acrylate (IBA), where the photochromic moiety resides within the soft p(BA) central portion. These block copolymers were made into films and their photochromic behaviour was compared to one another and to those of corresponding dye-p(BA) conjugates that were cast in the rigid host matrix. 104 Chapter 4. The Importance of Macromolecular Architecture… ______

4.2 Results and Discussion

Hydroxyl-functionalized naphthopyrans 1 and 311 were synthesized in high yield, as described in previous publications,3,9,12 and then converted to the red-colouring isobutyrate derivatives 2 and 4 via simple esterification routes (Scheme 1). With the aim of scrutinizing the effect of polymer conjugation on the performance of the dye, these electronically equivalent controls served as reference points for our tests.

Scheme 1. Synthesis of Photochromic Control Compounds 2 and 4

Photochromic ATRP initiators 5 and 7 were also prepared by esterification of these hydroxyl-functionalized precursors with 2-bromoisobutyryl bromide. In the case of photochromic initiator 6, the aliphatic branching agent, 2,2-bis- (hydroxymethyl)propionic acid,13 was first converted to 2,2-bis(2-bromo-2 methylpropanoyloxymethyl)propanoic acid,14-16 using 2-bromoisobutyryl bromide. The corresponding acid chloride was then coupled to the hydroxyl-functionalized naphthopyran 1 (Scheme 2).

4.2.1 Naphthopyran-Polymer Conjugate Synthesis.

ATRP was used to synthesize various naphthopyran-p(BA) conjugates of increasing molecular weight (Mn, g/mol), as depicted in Scheme 2. All homopolymerizations were carried out in solution at 90 C with CuBr and 4,4'-dinonyl-2,2'-bipyridine (dNbpy) as the catalyst system. In order to gauge the viability of these conditions, evolution plots were generated (Figures 3, 4, and 5). These displayed a linear progression of Mn with conversion, with values similar to those expected theoretically for a controlled radical process and with low PDIs (<1.2) throughout. Furthermore, first-order kinetic plots for each of these polymerizations showed a near-linear relation with time (Appendix 2, page A6).

105 Chapter 4. The Importance of Macromolecular Architecture… ______

Scheme 2. ATRP synthesis of naphthopyran-poly(n-butyl acrylate) conjugates displaying molecular weights of purified samples tested in the study; (dNbpy = 4,4'- dinonyl-2,2'-bipyridine; n-BA = n-butyl acrylate).

The specific characteristics of the polymerizations that generated the conjugates are shown in Table 1 and the final Mn values of purified samples which were subsequently tested are displayed in Scheme 2. The corresponding GPC traces display a high molecular weight shoulder for end-functional polymers 8d and 8e (Appendix 2, pages A12-A13). This can be attributed to long chain branching which occurs at higher conversions in polyacrylates as a result of back-biting and scission processes.17

106 Chapter 4. The Importance of Macromolecular Architecture… ______

Figure 3. Evolution of polydispersity () and molecular weight () with conversion for the ATRP of n-butyl acrylate with initiator 5 at 90 C in benzene where [monomer]/[CuBr]/[4,4’-dinonyl-2,2’-bipyridine]/[5]=100:1:2:1. Calculated molecular weight (---) by NMR conversion using the equation Mn = ((monomer MW) × ([monomer]/[5]) × (NMR conversion)) + (MWof 5). Polymerization times ranged from 2 to 12.8 h.

Figure 4. Evolution of polydispersity () and molecular weight () with conversion for the ATRP of n-butyl acrylate with initiator 6 at 90 C in benzene where [monomer]/[CuBr]/[4,4'-dinonyl-2,2'-bipyridine]/[6] = 200:1:2:1. Calculated molecular weight (---) by NMR conversion using the equation Mn = ((monomer MW) × ([monomer]/[6]) × (NMR conversion)) + (MW of 6). Polymerization times ranged from 1 to 3.5 h.

107 Chapter 4. The Importance of Macromolecular Architecture… ______

Figure 5. Evolution of polydispersity () and molecular weight () with conversion for the ATRP of n-butyl acrylate with initiator 7 at 90 C in benzene where [monomer]/[CuBr]/[4,4'-dinonyl-2,2'-bipyridine]/[7] = 200:1:2:1. Calculated molecular weight (---) by NMR conversion using the equation Mn = ((monomer MW) × ([monomer]/[7]) × (NMR conversion)) + (MW of 7). Polymerization times ranged from 1.3 to 5.7 h.

Figure 6. Evolution of polydispersity () and molecular weight () with conversion for the ATRP of n-butyl acrylate with monomer 11 (2 %) at 90 C in benzene, where [monomers]/[CuBr]/[4,4'-dinonyl-2,2'-bipyridine]/[ethyl 2-bromoisobutyrate initiator] = 150:1:2:1. Calculated molecular weight (---) by NMR conversion using the equation Mn = {(n-butyl acrylate MW) × ([n-butyl acrylate]/[ethyl 2-bromoisobutyrate]) × (NMR conversion)} +{(11 MW) × ([11]/[ethyl 2-bromoisobutyrate]) × (NMR conversion)} + (MW of ethyl 2-bromoisobutyrate). Polymerization times ranged from 1 to 8.2 h.

108 Chapter 4. The Importance of Macromolecular Architecture… ______

Table 1. Polymerization Characteristics of naphthopyran-poly(n-butyl acrylate) conjugates.

Time [monomer] Sample Typea Conv. (%)c exp. M d theo. M e PDI (mins)b /[initiator] n n 8a homopol. 60 20 130 3,360 3,332 1.18 8b homopol. 240 36 100 5,710 5,211 1.10 8c homopol. 360 48 100 8,150 6,769 1.10 8d homopol. 770 68 100 11,600 9,303 1.12 8e homopol. 960 88 130 18,700 15,183 1.16 10a homopol. 75 15 200 4,900 4,611 1.14 10b homopol. 90 19 200 5,800 5,498 1.13 10c homopol. 140 24 200 7,100 6,854 1.12 10d homopol. 200 34 200 1,0200 9,551 1.11 10e homopol. 340 47 200 13,900 12,781 1.11 9a homopol. 60 22 100 3,820 3,672 1.16 9b homopol. 60 22 200 5,940 6,492 1.20 9c homopol. 80 29 200 7,830 8,210 1.17 9d homopol. 140 38 200 10,300 10,645 1.15 9e homopol. 210 51 200 14,500 1,3900 1.12 13a copol. 60 20 150 4,270 4,040 1.23 13b copol. 130 27 150 5,950 5,386 1.17 13c copol. 490 48 150 11,500 9,423 1.15 14a copol. 120 67 135 14,400 12,000 1.13 a homopol. = poly(n-butyl acrylate) homopolymer as shown in Scheme 2; copol. = poly(n-butyl acrylate)-co-poly(naphthopyran) as shown in Scheme 3. b Polymerizations for 8a-8e performed with n-butyl acrylate at 90 °C in benzene with [monomer]/[5] as indicated and [CuBr]/[4,4'-dinonyl-2-2'-bipyridine] = 1:2; Polymerizations for 9a-9e performed with n-butyl acrylate at 90 °C in benzene with [monomer]/[6] as indicated and [CuBr]/[4,4'-dinonyl-2-2'-bipyridine] = 1:2; Polymerizations for 10a-10e performed with n-butyl acrylate at 90 °C in benzene with [monomer]/[7] as indicated and [CuBr]/[4,4'-dinonyl-2-2'-bipyridine] = 1:2; Polymerizations for 13a-13c performed with n-butyl acrylate and 11 (98:2 by mole respectively) at 90 °C in benzene with [monomers]/[ethyl-2-bromo isobutyrate] as indicated and [CuBr]/[4,4'-dinonyl-2-2'- bipyridine] = 1:2; Polymerization for 14a performed with n-butyl acrylate and 12 (99:1 by mole respectively) at 90 °C in benzene with [monomers]/[BBMP] as indicated and [CuBr]/[4,4'-dinonyl-2-2'-bipyridine] = 1:2. c Determined by 1H NMR analysis of d polymerization mixture. Crude Mn value determined by GPC with THF as eluent with poly(n-butyl acrylate) equivalents which were obtained using Mark-Houwink parameters applied to a PS calibration e Calculated based on monomer conversion plus initiator molecular weight. (Example 1H NMR spectra displayed in Appendix 2, pages A7-A10).

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Copolymerizations of naphthopyran acrylate 11 with n-BA were carried out using the same polymerization conditions (catalyst system, temperature, and solvent, Figure 6) to yield 13a-13c. Made only from acrylates, these copolymers are expected to contain a random distribution of naphthopyrans along each polymer chain. The final composition and molecular weights of each conjugate are shown in Scheme 3, their GPC traces and first-order kinetic plots are displayed in Appendix 2 and their specific polymerization characteristics are shown in Table 1. Conversions were found to be no higher that 50 %, even after 8 h, and in each case the remaining quantity of unreacted photochromic acrylate proved difficult to remove from the bulk polymer. In contrast, the purification of polymers made out of photochromic initiators was far less problematic since all photochromic moieties were utilized in the polymerization process. A small proportion of naphthopyran methacrylate 12 was copolymerized with n-BA using the di-functional ATRP initiator, n-butyl 2,2-bis(2-bromo-2- methylpropanoyloxymethyl) propanoate (BBMPP, Scheme 3) to yield 14a. It was expected that an earlier and more complete uptake of the naphthopyran monomer would occur since its reactivity ratio in the copolymerization mixture would be greater than that of n-BA.18 Consequently, the crude polymerization mixture was found to contain no unreacted monomer by the end of the polymerization time (67 % conversion). The di-functional nature of the ATRP initiator BBMPP also means that the naphthopyran moieties reside in the central portion of the polymer, within a Y-branched structure, depicted as “E” in Figure 2. As shown in Scheme 4, several Y-branched mid-functional naphthopyran-p(BA) conjugates were synthesized using di-functional initiator 6 and then chain extended with IBA to produce 15a-15c. The initial homopolymerizations with n-BA were carried out in solution analogously to 9a-9e and are labelled as p(BA) macroinitiator in Table 2. Block copolymer 16a was made directly from conjugate 14a as in Scheme 5. These ABA triblock copolymers, with naphthopyran/s contained within the middle soft section, were fabricated into films for testing. The composition of the polymers was ascertained by 1H NMR, with specific examples displayed in Appendix 2 (pages A10- A11). Resonance peaks corresponding to the photochromic functionality, as well as the initiator scaffold are evident in each. These aspects are confirmed by comparison of the spectrum of the conjugate with that of the initiator. The GPC traces showed successful block extension (Figures 7-10), a process that was made possible by the living nature of

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ATRP. The polymers displayed good film processing properties and phase separated on , as evidenced by DSC analysis which showed two separate glass transition temperatures (Tg) for each.

Scheme 3. ATRP synthesis of naphthopyran-poly(n-butyl acrylate) copolymers displaying molecular weights and compositions of purified samples that were tested. (NP = naphthopyran monomer, dNbpy = 4,4’dinonyl-2,2’-bipyridine, n-BA = n-butyl acrylate).

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Scheme 4. ATRP synthesis of naphthopyran ABA triblock copolymers 15a-15c (with poly(isobornyl acrylate) as the A block sections and poly(n-butyl acrylate) as the B block section), with molecular weights and compositions of purified samples tested. (i) Polymerization of n-butyl acrylate with initiator 6 at 90 °C in benzene; (ii) block extension of purified poly(n-butyl acrylate) macroinitiator with isobornyl acrylate at 90 °C in benzene; refer to Table 2 for specific polymerization characteristics; NP = naphthopyran, n-BA = n-butyl acrylate, IBA = isobornyl acrylate.

Scheme 5. ATRP synthesis of naphthopyran ABA triblock copolymer 16a (with poly(isobornyl acrylate) as the A block sections and (naphthopyran)-co-poly(n-butyl acrylate) as the B block section), displaying molecular weight and composition of purified sample tested; NP = naphthopyran, n-BA = n-butyl acrylate, IBA = isobornyl acrylate.

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Figure 7. Overlaid and normalized GPC traces of block copolymer formation; A = mid- functional naphthopyran-poly(n-butyl acrylate) macroinitiator; B = naphthopyran- poly(n-butyl acrylate)-b-poly(isobornyl acrylate) triblock copolymer, 15a.

Figure 8. Overlaid and normalized GPC traces of block copolymer formation; A = mid- functional naphthopyran-poly(n-butyl acrylate) macroinitiator; B = naphthopyran- poly(n-butyl acrylate)-b-poly(isobornyl acrylate) triblock copolymer, 15b.

Figure 9. Overlaid and normalized GPC traces of block copolymer formation; A = mid- functional naphthopyran-poly(n-butyl acrylate) macroinitiator; B = naphthopyran- poly(n-butyl acrylate)-b-poly(isobornyl acrylate) triblock copolymer, 15c.

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Figure 10. Overlaid and normalized GPC traces of block copolymer formation; 16a from 14a.

Table 2. Polymerization Characteristics of Naphthopyran poly(n-butyl acrylate)-b- poly(isobornyl acrylate) triblock copolymers.

Time Conv. [monomer]/ exp. theo. Tg Type a b c d PDI e (mins) (%) [initiator] Mn Mn (ºC) p(BA) macroinitiator 60 52 100 7,270 7,530 1.13 15a 250 61 154 30,000 26,800 1.24 -46, 47 p(BA) 80 35 200 9,740 9,825 1.19 macroinitiator 15b 250 67 150 36,700 30,500 1.22 -48, 48 p(BA) macroinitiator 170 58 200 16,500 15,759 1.14 15c 250 42 144 28,400 28,800 1.17 -41, 74 16a 220 40 150 27,000 28,000 1.17 -44, 80 a For 15a polymerization of n-butyl acrylate with initiator 6 at 90 °C in benzene, [monomer]/[CuBr]/[4,4'-dinonyl-2-2'-bipyridine]/[6] = 100:1:2:1, and block extension of purified poly(n-butyl acrylate) macroinitiator with isobornyl acrylate at 90 °C in benzene, [monomer]/[CuBr]/[4,4'-dinonyl-2-2'-bipyridine]/[macroinitiator] = 154:1:2:1; For 15b polymerization of n-butyl acrylate with initiator 6 at 90 °C in benzene, [monomer]/[CuBr]/[4,4'-dinonyl-2-2'-bipyridine]/[6] = 200:1:2:1, and block extension of purified poly(n-butyl acrylate) macroinitiator with isobornyl acrylate at 90 °C in benzene, [monomer]/[CuBr]/[4,4'-dinonyl-2-2'-bipyridine]/[macroinitiator] = 150:1:2:1; For 15c polymerization of n-butyl acrylate with initiator 6 at 90 °C in benzene, [monomer]/[CuBr]/[4,4'-dinonyl-2-2'-bipyridine]/[6] = 200:1:2:1, and block extension of purified poly(n-butyl acrylate) macroinitiator with isobornyl acrylate at 90 °C in benzene, [monomer]/[CuBr]/[4,4'-dinonyl-2-2'-bipyridine]/[macroinitiator] = 144:1:2:1; For 16a block extension of p(n-butyl acrylate) macroinitiator 14a (see polymerization conditions in Table 1) with isobornyl acrylate at 90 °C in benzene, [monomer]/[CuBr]/[4,4'-dinonyl-2-2'-bipyridine]/[macroinitiator]=150:1:2:1; b Determined by 1H NMR analysis of polymerization mixture. c p(n-butyl acrylate) macroinitiator Mn determined by GPC (THF) in poly(n-butyl acrylate) equivalents using Mark-Houwink parameters on a PS calibration; block copolymers estimated by 1H NMR of purified samples. d Calculated based on monomer conversion plus macroinitiator molecular weight. Example 1H NMRs displayed in Appendix 2. e Determined by DSC, refer to experimental details.

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4.2.2 Evaluation of Photochromic Performance: Cast-in Lenses.

The development of intense colour in a photochromic test sample, such as a cured lens or a film, is induced by incident irradiation with UV light. Upon cessation of the UV light the samples decolourize spontaneously in the dark due to the thermal back-reaction which occurs as the naphthopyran open form undergoes ring closure. Spectrokinetic properties can be studied by monitoring absorption density with time at the max of the coloured form. The sample is continuously irradiated for 1000 s, and then the decolouration kinetics of the sample are investigated in the dark at 20 C upon cessation of UV irradiation. The following empirical biexponential equation19,20 was used to analyze the thermal ring closure kinetics of each sample:    k1t  k2t  A(t) A1e A2e Ath where A(t) is the optical density at max of the open form; A1 and A2 are the contributions to the initial optical density A0; k1 and k2 are exponential decay rate constants of fast and slow components respectively and Ath is the residual colouration

(offset). The parameter A0 is the absorbance level achieved after 1000 s of continuous irradiation. This equation has been used frequently to represent and compare the decolouration behaviour of both spirooxazines6-8 and naphthopyrans3,9,12 within solid media and has consistently fitted our decolouration curves with correlation coefficients (R) greater than 0.99.

Evaluation of T1/2 values, which is the time taken for the sample to fade to half of initial absorbance value, provides insight into the overall kinetics. The photochromic properties of the lens samples are displayed in Table 3 and those of the cast films comprising the block copolymers are shown in Table 4. Photochromic lens samples were prepared by adding the photochromic conjugates (or controls) individually to a lens monomer formulation at a set concentration level (1.5 ×10-7 mol of photochromic conjugate per gram of host matrix composition). This lens monomer formulation comprises poly(ethylene glycol) 400 dimethacrylate (PEGDMA) and 2,2'-bis(4-methacryloxyethoxy)phenylpropane (ethoxylated bisphenol A dimethacrylate, EBPDMA) in a 1:4 weight ratio with 0.4 mass % of azobis(isobutyronitrile) (AIBN). The formulations were mixed thoroughly and thermally cured in a mould to produce optically clear test samples.

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Table 3: Photokinetic analysis of the decolouration of poly(n-butyl acrylate)- naphthopyran conjugates and their corresponding controls in host matrix.a

k k T d sample max M b A c 1 A 2 A A 1/2 (nm) n 0 (min-1) 1 (min-1) 2 th (s) 2 500 - 0.93 0.6095 0.6415 0.0699 0.0975 0.2394 123.0 8a 500 2,780 1.02 0.7356 0.7117 0.0743 0.0478 0.2226 88.5 8b 496 5,800 1.06 0.7920 0.7321 0.0864 0.0331 0.2216 79.5 8c 496 8,000 1.11 0.8192 0.7368 0.0844 0.0303 0.2229 76.5 8d 495 11,300 1.11 0.8801 0.7124 0.7138 0.0555 0.2260 75.0 8e 495 18,100 1.19 0.8543 0.7396 0.0556 0.0253 0.2225 73.2 4 500 - 0.90 0.5943 0.6334 0.0763 0.1127 0.2346 130.0 10a 492 4,900 1.06 0.8151 0.7461 0.0878 0.0318 0.2096 75.0 10b 492 5,800 1.09 0.8483 0.7594 0.0634 0.0213 0.2080 70.5 10c 492 7,100 1.07 0.8800 0.7608 0.0551 0.0202 0.2063 67.5 10d 492 10,200 1.04 0.8782 0.7677 0.0534 0.0194 0.2005 66.0 10e 492 13,900 1.09 0.8961 0.7658 0.0723 0.0206 0.2037 66.0 2 500 - 0.92 0.5950 0.6630 0.0856 0.1004 0.2184 120.0 9a 497 3,090 1.11 1.0319 0.7352 0.0740 0.0237 0.2297 62.0 9b 495 6,090 1.08 1.0267 0.7374 0.0774 0.0238 0.2307 62.0 9c 495 7,330 1.21 1.0647 0.7356 0.0648 0.0231 0.2304 59.0 9d 495 10,500 1.19 1.1159 0.7439 0.0505 0.0185 0.2268 56.0 9e 495 15,200 1.21 1.1168 0.7453 0.0658 0.0171 0.2285 56.0 13a 495 4,100 0.80 0.9216 0.7435 0.0414 0.0248 0.2174 66.0 13b 495 5,600 1.01 0.8642 0.7351 0.0736 0.0361 0.2189 73.2 13c 495 12,100 1.76 0.8406 0.7544 0.0887 0.0333 0.1999 70.5 14a 495 15300 1.92 0.9802 0.7316 0.1727 0.0513 0.2120 65.0 a Host matrix = PEGMA:EBPDMA 1:4 mass composition. Cured samples initially irradiated at 350-400 nm for 1000 seconds, then decolouration monitored at max of the b coloured form at 20 °C in the dark for 4800 seconds. Molecular Weight (Mn, g/mol) of purified conjugates estimated from GPC analysis: poly(n-butyl acrylate) equivalents obtained using Mark-Houwink parameters on a PS calibration. c Measured absorbance intensity at onset of thermal decolouration period. d Time taken for the initial absorbance value, A0, to decay to half its value.

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Both end-functional and mid-functional naphthopyran-p(BA) conjugates displayed superior decolouration rates compared to their controls in the lens host matrix (Table 3). For each type the rates mildly increased with molecular weight of conjugated tail showing that chain length can be used to finely tune the rate of decay. It has also been discovered that when both a short and hard block segment is inserted near a photochromic, followed by a lubricating section, this allows a much wider range of switching speeds to be accessed.21 This has also been the case when an aromatic Y- branching linker is used to synthesize mid-functional p(BA) conjugates.9 In light of this, the level of tuneability appears to be dependent on the nature of the linker near the photochromic moiety. As seen in Figure 11, a comparison of the decolouration performance of end- functionalized conjugates 8a-8e with that of mid-functionalized conjugates, 9a-9e and 10a-10e, shows that when the photochromic is positioned in the centre of the chain, it responds favourably with lower T1/2 values and with an overall improved performance per chain length. Therefore, two polymer chains per photochromic moiety provide better encapsulation within the rigid host matrix. Furthermore, placing the photochromic pendant along the chain, as 9a-9e, gives superior performance compared to directly placing it within the chain, as 10a-10e.

Figure 11. Thermal decolouration comparison: measured T1/2 values (in seconds) of naphthopyran-poly(n-butyl acrylate) conjugates 8a-8e, 9a-9e and 10a-10e vs. their corresponding molecular weight in the host matrix, PEGDMA:EBPDMA (1:4).

This is also reflected in the major rate constant k1, which, when compared directly to that of the control, is markedly higher for mid-functional conjugates 9a-9e (Figure -1 12). The values in fact start to approach twice the value of the control (k1=0.595 min )

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and this effect arises at a relatively modest molecular weight of conjugated tail (e.g., 9d -1 with Mn 10,500 g/mol, k1=1.116 min ).

Colouration values, A0, of samples prepared from conjugates 8a-8e, 9a-9e, and 10a- 10e, which have exactly one dye moiety per polymer chain, can also be directly compared to that of their controls since they all contained equivalent concentrations of dye. As seen in Table 3, the values for these conjugates were 1.1-1.3 times greater than their controls. This is in agreement with previous work which showed that a higher level of colouration was associated with samples displaying faster kinetics.9

Figure 12. Thermal decolouration comparison: k1(conjugate) / k1(control) of naphthopyran-poly(n-butyl acrylate) conjugates (8a-8e, 9a-9e, 10a-10e, 13a-13c and 14a) when cast in the host matrix PEGDMA:EBPDMA (1:4).

Figure 12 also shows that naphthopyran-p(BA) linear random copolymers 13a-13c showed decay speeds comparable to the mid-functional (homopolymer) conjugates, 10a-10e, however, per chain length their performance was found to be superior to that of end-functional conjugates, 8a-8e. This is also in agreement with previous results which compared various naphthopyran copolymers with end-functional conjugates10 and can be ascribed to greater association of pendant naphthopyran moieties with surrounding n-BA units within the copolymer. Interestingly, increases in chain length were correlated with a tuning down of response (k1 goes down from 13a to 13c). This is most likely due to increasing naphthopyran units per chain along the series that would decrease chain mobility. Overall, from the point of view of incomplete uptake of monomer units during the copolymerization and an inability to regulate the exact location of the dye in the chain, this approach seems less attractive overall compared to

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Y-branching architecture (9a-9e) which provides both a precise and well-encapsulated location for the dye in the chain. Copolymer 14a also incorporates a Y-branched structure in which the naphthopyran moieties reside in the central portion of the polymer, as depicted in Figure 2 and Scheme 3. Its kinetics within the host matrix were in fact found to be superior to those of all the linear copolymers, 13a-13c, indicating that this system offers better encapsulation per chain length. Hypsochromic (blue) shifts in wavelength of the coloured form were seen for the photochromic conjugates in the host matrix compared to the controls. This can be attributed to effective shielding of naphthopyran moieties, as a result of conjugation to p(BA), from the more polar matrix environment that comprises substantial PEG units. This is particularly evident for conjugates 10a-10e which displayed the largest shift (492 nm), indicating a significant insulation and encapsulation effect. However, given that these structures were second best overall in terms of enhancing kinetics, the weight of two polymer chains radiating from a central, non-pendant photochromic moiety seems to offset this benefit. Overall, Y-branched structures 9a-9e, which contain two polymer arms per mid- functional and pendant photochromic moiety, displayed the fastest kinetics and the most impressive colourabilities. In previous studies the T1/2 value for naphthopyran control dye 2, measured in toluene at 20 C, was found to be 63 s and 52 s for its corresponding propionyl derivative.3,12 The ability of the photochromic-polymer conjugates in a rigid host to surpass solution kinetics is unlikely, strongly suggesting that the Y-branching technology presented here, which achieved a T1/2 value of 56 s (for 9d and 9e), has reached a limit. Extra branching points are unlikely to offer any additional kinetic benefits. In conclusion, these results show that by changing the arrangement and geometry of units comprising the photochromic-polymer conjugate, one can further tune the switching behaviour within a rigid host and this is possible without making modifications to the bulk host material.

4.2.3 Photochromic Films: ABA Triblock Copolymers.

The tuning of naphthopyran switching in bulk films has already been achieved using block copolymers synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization.22 These structures were linear block copolymers made with naphthopyran monomers copolymerized into the soft poly(methyl acrylate) sections of 119 Chapter 4. The Importance of Macromolecular Architecture… ______

the block copolymers. The hard sections comprised either polystyrene or poly(methyl methacrylate), both optically clear, high Tg polymers. Controlled radical polymerization techniques can be used to synthesize hard-soft block copolymers that phase separate with the photochromic encapsulated into the low Tg environment of the soft phase. The soft local environment allows switching speed to be enhanced while the continuous high

Tg matrix maintains structural integrity at higher than ambient temperatures. This approach was explored in this paper using ATRP with the formation of ABA triblock copolymers with a promising arrangement and choice of building units for photochromic kinetics in which Y-branched naphthopyran-p(BA) macroinitiators were block extended with poly(isobornyl acrylate), p(IBA) (Schemes 4 and 5). An ideal system of encapsulation for the dye was afforded by its mid-placement within the fluid phase of p(BA), and the surrounding p(IBA) was chosen as the hard section of the block copolymers because of its high Tg, hardness, comparable properties to poly(methyl methacrylate) and polystyrene, and ease of polymerization.23 Films of the block copolymers were prepared by casting the polymer solutions, followed by annealing for 16 h. The photochromic properties of films comprised of 15a-15c and block copolymer 16a, made from Y-branched p(BA) macroinitiator 14a, are presented in Table 4.

Table 4. Photokinetic analysis of the decolouration of naphthopyran tribock copolymer films.

[n-BA] k k t d sample M b A c 1 A 2 A A 1/2 n / [IBA] 0 (min-1) 1 (min-1) 2 th (s) 15a 30000 1 : 2 1.19 0.5215 0.5418 0.0646 0.1996 0.2180 178.0 15b 36700 1 : 1.9 2.00 0.6680 0.6410 0.0739 0.1345 0.1954 110.0 15c 28400 2 : 1 1.42 0.9743 0.7860 0.0249 0.0149 0.1968 60.0 16a 27000 2.1 : 1 1.27 0.7360 0.7542 0.0804 0.0515 0.1756 80.0 a Samples initially irradiated at 350-400 nm for 1000 seconds, then decolouration monitored at max of the coloured form (488 nm for all), at 20 °C in the dark for 4800 b seconds. Molecular Weight (Mn, g/mol) of purified block copolymers estimated from 1H NMR c Measured absorbance intensity at onset of thermal decolouration period. d Time taken for the initial absorbance, A0, to decay to half its value.

Figure 13 shows the overlaid thermal decolouration curves of the block copolymer films and clearly show that a high level of tuning is achievable using this approach. It is the composition of the block copolymers that is primarily implicated; the fastest decolouration time was achieved for 15c (T1/2 60 s), which contained the highest

120 Chapter 4. The Importance of Macromolecular Architecture… ______

proportion of p(BA) and the highest quantity of n-BA repeat units and the slowest time was achieved by the 15a (T1/2 178 s) which contained the lowest proportion of p(BA) and also the lowest quantity of n-BA repeat units. As distinct from the cast-in approach used for the lenses, here the photochromic conjugates themselves comprise the matrix. The extent of separation of the photochromic moieties from the hard p(IBA) component is therefore highly dependent on the amount of p(BA) encapsulating them. The film comprised of 16a, which also contained a high proportion of p(BA), was second in speed to 15c (T1/2 80 s vs T1/2 60 s). Furthermore, 14a, which is the precursor to 16a, displayed a higher colouration value, A0, in the lens compared to all the conjugates, indicating more than one naphthopyran moiety is present per chain. As described above, the photochromic moieties of this conjugate reside within the central part of the polymer with proximity to one another, which increases their local rigidity and reduces the mobility of polymer chains. With reference to Table 3, this is supported by the fact that the decolouration behaviour of 14a within the lens matrix is a lot slower than conjugate 9e (T1/2 65 s vs. T1/2 56 s), even though both have approximately the same molecular weight.

Figure 13. Thermal decolouration curves (monitored in the dark at 20 °C after UV irradiation for 1000 seconds) of naphthopyran p(n-butyl acrylate)-b-p(isobornyl acrylate) block copolymers.

Lastly, these studies display an overall tendency of the casting-in method to provide faster kinetics in comparison to the films. The macroinitiators used to synthesize block copolymers 15a-15c had the same structures and similar Mn values (7,270-16,200 g/mol) as 9c-9e (Mn 7,330-15,200 g/mol). However, the corresponding block copolymer

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-1 films of 15a-15c displayed slower kinetics (k1=0.52-0.97 min ) compared with the -1 kinetics displayed by conjugates 9c-9e (k1 = 1.06-1.12 min ) in the lenses. Furthermore, -1 comparing the kinetics of 14a in the lens matrix (k1=0.98 min ) with that of the film -1 16a (k1=0.74 min ), the same trend is displayed. The lens material is a continuous 5 cross-linked network with a measured Tg of ~120 C, so chain mobility within the local environment of the photochromic rests heavily on the ability of p(BA) to partition away from the host matrix. This will be enhanced by the discontinuity and incompatibility between the two components. However, in the case of the films, the block copolymer comprises the bulk matrix, where the ability of the two phases to effectively separate is critical and highly dependent on processing conditions. In order to bring kinetics between the two matrices closer together, this aspect could be further examined.

4.3 Conclusion

ATRP was used to synthesize naphthopyran-polymer conjugates with a variety of architectures. First, within a lens rigid matrix, an investigation of various p(BA) homopolymers showed that mid-functional placement of the dye, made possible using a di-functional photochromic initiator, gave superior kinetics per chain length of conjugated polymer. Moreover, it was preferable to have the dye pendant from the chain as opposed to directly within the chain. Analysis of naphthopyran-p(BA) copolymers also showed that having the dye pendant along the chain as a monomer unit was also attractive, however, the ability to tune response via chain length could not be achieved using random copolymers. A better approach was a gradient copolymer system made with a non-photochromic di-functional initiator that allowed total incorporation of the naphthopyran methacrylate within the middle portion of the polymer chains. The formation of copolymers with the photochromic encapsulated in the middle of a Y-branched central soft section was made possible using ABA triblock geometry. Their films showed enhanced tuning of response dependent on the overall proportion of soft section inhabited by the photochromic. It is interesting that regardless of the method used to assemble a photochromic material, such as casting-in a lens host or film formation, the ability to manipulate polymer architecture is appealing because it provides an extra avenue to control photochromic properties, beyond chain length and rigidity (Tg).

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4.4 Experimental Details

Materials. The synthesis of methyl 6-hydroxy-2-(4-methoxyphenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (1), methyl 6-(isobutyryloxy)-2-(4-methoxy- phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (2), methyl 6-(2-bromo-2- methylpropanoyloxy)-2-(4-methoxy-phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5- carboxylate (5), methyl 6-(acryloyloxy)-2-(4-methoxy-phenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (11) and methyl 6-(methacryloyloxy)-2-(4-methoxy- phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (12) has been described by us previously in literature.3 2,2-Bis(2-bromo-2-methylpropanoyloxymethyl)propanoic acid was prepared using a procedure adapted from literature.14-16 All chemicals (reagents and solvents) used for synthesis were of high purity and used as received unless otherwise stated. n-Butyl acrylate (99+ % purity, Aldrich) was purified by passing through aluminum oxide 90, activated basic (0.063 - 0.200 nm, Merck) to remove inhibitors and then flash vacuum distilled prior to use. Isobornyl acrylate (tech grade, Aldrich) was purified by passing through aluminum oxide 90, activated basic (0.063 - 0.200 nm, Merck) to remove inhibitors. All reagents were purchased from Aldrich Chemical Co. unless otherwise stated. All chromatography was performed using silica gel (Kieselgel Merck 60, 0.040 - 0.063 mm) and TLC was performed on Merck Silica

60F254 plates.

General Experimental Measurements. Gel permeation chromatography (GPC) was performed on a Waters 515 HPLC pump and Waters 717 Plus Autosampler equipped with Waters 2414 refractive index detector and 3 × Mixed-C (7.5 mm × 300 mm, 5 m particle size, linear molecular weight range 200 - 2,000,000) and 1 Mixed E PLgel column (7.5 mm × 300 mm, 3 m particle size, linear molecular weight range up to 30,000) from Polymer Laboratories. Tetrahydrofuran (THF) with a flow rate of 1.0 mL min-1 was used as eluent at 22 ± 2 °C. Molecular weights for p(BA)-naphthopyran conjugates were calculated via calibration with narrow polydispersity polystyrene standards (Polymer Laboratories) ranging from 600 to 7.5 × 106 g/mol. Molecular 24 Weights (Mn) were converted to p(BA) equivalents using Mark-Houwink parameters on the PS calibration. Number (Mn) and weight-average (Mw) molecular weights were evaluated using Waters Millennium/Empower software. A third-order polynomial was used to fit the log M vs. time calibration curve, which was linear across the molecular weight ranges.

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1H (400 MHz) and 13C NMR (100 MHz) spectra were obtained with a Bruker Av400 spectrometer at 25 °C. Spectra were recorded for samples dissolved in deuterated solvent and chemical shifts are reported as parts per million from external tetramethylsilane. Monomer conversions were obtained from the 1H NMR spectra. The resonances integrated to obtain conversions for n-BA polymerizations were the vinyl peaks at 5.8, 6.2 and 6.4 ppm (monomer only) and the OCH2- peaks at 3.9 - 4.1 ppm (monomer and polymer). The resonances integrated to obtain conversions for IBA polymerizations were the vinyl peaks at 5.8, 6.2 and 6.4 ppm (monomer only) and the isobornyl -CH- peak at 4.60 - 4.85 ppm (monomer and polymer). The compositional ratio of the copolymers (including triblocks) was calculated by 1H NMR via the integrated peak intensity ratio of naphthopyran vs. that of the polymers. All other spectra were recorded on Bruker Av400 spectrometer. Positive ion EI mass spectra were run on a ThermoQuest MAT95XL mass spectrometer using ionization energy of 70 eV. Accurate mass measurements were obtained with a resolution of 5000-10000 using PFK as the reference compound. Thermal Analysis by Differential Scanning Calorimetry (DSC) was performed in order to determine the Tg of the triblock copolymers. This was carried out using a Mettler Toledo DSC821 machine with temperature and heat flow calibrated using indium and zinc as reference substances. Samples (~10 mg) were heated under nitrogen from -50 °C to 150 °C at 10 °C/minute. The Tg values were taken from the midpoints of the heat flow changes observed in the second heat cycle.

Photochromic Analysis. Under continuous UV irradiation, the photochromic responses of the samples (cured lenses or cast films) were analyzed on a light table composed of a Cary 50 spectrophotometer for measuring absorbance values and a 160 W Oriel xenon lamp as an incident light source. A series of two filters (Edmund Optics 320 cut-off and bandpass filter U-340) were used to restrict the output of the lamp to a narrow band (350 - 400 nm). The samples were maintained at 20 °C and monitored at the maximum absorbance of the coloured form for a period of 1000 s. Then the thermal decolouration was monitored in the absence of UV irradiation for a further 4800 s.

Synthesis of methyl 6-hydroxy-2-(4-(2-hydroxyethoxy)phenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (3). The complete procedure for synthesis of the title compound can be derived from what is already reported in literature.17 4- Hydroxybenzophenone was firstly converted to 4-(2-hydroxyethoxy)benzophenone

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using bromoethanol and Na2CO3. This was then converted to 1-(2- hydroxyethoxy)phenyl)-1-phenyl-prop-2-yn-1-ol using 2 molar equivalents of (trimethylsilyl)acetylene and n-butyl lithium (1.6 M in hexane) with respect to the benzophenone. The title compound was then derived from 1-(2-hydroxyethoxy)phenyl)- 1-phenyl-prop-2-yn-1-ol and methyl 1,4-dihydroxynapthalene-2-carboxylate, after purification by column chromatography (silica gel 60, Ethyl Acetate/Hexane), as a 1 bright yellow solid (2.3 g, 75%). H NMR (400 MHz, d6-acetone) : 3.80 - 3.83 (m, 2H,

CH2CH2OH), 3.87 (t, 1H, J 5.80 Hz, OH), 4.00 (t, 2H, J 4.85 Hz, CH2CH2OH), 4.06 (s,

3H, COOCH3), 6.38 (d, J 10.0 Hz, 1H, pyran-H), 6.87 (apparent d, J 8.8 Hz, 2H, ArH), 7.22 - 7.26 (m, 1H, ArH), 7.31 - 7.35 (m, 2H, ArH), 7.47 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.52 (d, J 10.0 Hz, 1H, pyran-H), 7.56 - 7.63 (m, 3H, ArH), 7.75 - 7.79 (m, 1H, ArH) 8.32 (d, J 8.4 Hz, 1H, ArH), 8.42 (d, J 8.4 Hz, 1H, ArH), 12.17 (s, 1H, 13 ArOH) ppm. C NMR (100 MHz, d6-acetone) : 53.8, 62.1, 71.3, 82.7, 104.0, 115.3, 115.6, 123.5, 125.2, 125.5, 126.7, 128.0, 128.4, 128.9, 129.5, 129.6, 129.7, 130.2, 131.6, 138.3, 142.6, 146.9, 157.9, 160.2, 173.6 ppm. Mass Spec (EI): m/z 468.1 ([M]+ 86%), 436.1 (84), 391.1 (31), 363.1 (20), 289.1 (21), 268.1 (39), 223.1 (27), 207.1 (25), 191.1 (39), 181.0 (26), 165.1 (23), 147.0 (25), 131.0 (36), 121.0 (24), 119.0 (28), 105.0

(25), 77.0 (29), 69.1 (100). Mass Spec (HR, EI): m/z 468.1568 (C29H24O6 requires 468.1573).

Synthesis of methyl 6-(isobutyryloxy)-2-(4-(2-(isobutyryloxy)ethoxy)phenyl))-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (4). To an ice-cooled solution of methyl 6-hydroxy-2-(4-(2-hydroxyethoxy)phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5- carboxylate 3 (0.2 g, 0.43 × 10-3 mol) and triethylamine (TEA) (0.36 mL, 2.57 × 10-3 mol) in dry dichloromethane (CH2Cl2) (10 mL) was added dropwise, isobutyryl chloride (0.18 mL, 1.72 × 10-3 mol) under argon. The solution was stirred with ice cooling for half an hour and was then left to stir for an additional 12 hrs at room temp. The solvent was evaporated under vacuum, the residue re-dissolved in diethyl ether (Et2O) (30 mL) and washed successively with 0.5M HCl, water, aqueous NaHCO3, water and brine. The organic layer was dried with MgSO4 and the solvent evaporated under vacuum. The crude product was purified by column chromatography (silica gel 60, CH2Cl2) giving 1 the product as a crunchy pink solid (200 mg, 77%). H NMR (400 MHz, d6-acetone) :

1.07 - 1.10 (m, 6H, 2 × CH3), 1.35 - 1.37 (m, 6H, 2 × CH3), 2.47 - 2.55 (m, 1H,

CH(CH3)2, 2.96 - 3.04 (m, 1H, CH(CH3)2, 3.92 (br s, 3H, COOCH3), 4.19 - 4.23 (m,

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2H, CH2CH2OAr), 4.35 - 4.38 (m, 2H, CH2CH2OAr), 6.47 (d, J 10.0 Hz, 1H, pyran-H), 6.91 - 6.98 (m, 3H, ArH), 7.28 - 7.82 (m, 10H, ArH), 8.45 (d, J 8.6 Hz, 1H, ArH) ppm. 13 C NMR (100 MHz, , d6-acetone) : 19.1, 19.3, 34.4, 34.7, 52.9, 63.3, 66.9, 83.6, 114.2, 115.1, 121.1, 121.8, 123.04, 123.2, 127.0, 127.3, 128.3, 128.4, 128.7, 128.8, 129.0, 129.1, 130.0, 137.8, 140.0, 145.9, 146.6, 159.3, 166.3, 175.4, 176.9 ppm.

Synthesis of methyl 6-(2-bromo-2-methylpropanoyloxy)-2-(4-(2-bromo-2- methylpropanoyloxy)ethoxy)phenyl))-2-phenyl-2H-naphtho[1,2-b]pyran-5- carboxylate, naphthopyran ATRP initiator (7). This compound was synthesized from 3 and 2-bromo-isobutyrylbromide using the same general procedure as above and isolated as a crunchy pink solid after purification by column chromatography (silica gel 1 60, 1:1 Et20/Hexane) (523 mg, 80%). H NMR (400 MHz, d6-acetone) : 1.86 (s, 6H, 2

× CH3), 2.13 (s, 6H, 2 × CH3), 3.94 (s, 3H, COOCH3), 4.24 - 4.29 (m, 2H,

CH2CH2OAr), 4.46 - 4.51 (m, 2H, CH2CH2OAr), 6.49 (d, J 10.0 Hz, 1H, pyran-H), 6.91 - 7.0 (m, 3H, ArH), 7.24 - 7.76 (m, 9H, ArH), 8.01 - 8.05 (m, 1H, ArH), 8.46 - 8.50 (m, 13 1H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 31.7, 31.9, 53.9, 57.3, 65.9, 67.4, 84.5, 115.0, 116.0, 121.8, 122.5, 123.7, 123.9, 127.8, 128.1, 128.8, 129.2, 129.8, 129.8, 129.9, 130.9, 138.6, 140.2, 146.5, 147.9, 160.0, 166.8, 171.1, 172.6 ppm.

Synthesis of 2,2-bis(2-bromo-2-methylpropanoyloxymethyl)propionate, naphthopyran ATRP initiator (6). Oxalyl chloride (579 mg, 4.60 × 10-3 mol) was added dropwise via syringe to a solution of 2,2-bis(2-bromo-2- 14-16 -3 methylpropanoyloxymethyl)propanoic acid (984 mg, 2.28 × 10 mol) in dry CH2Cl2 (10 mL), followed by one drop of DMF. The reaction was allowed to reach completion after stirring for 2.5 hrs at room temperature. The excess oxalyl chloride was then removed on the rotary evaporator by stripping with several portions of dichloroethane to give the corresponding acid chloride, 2,2-bis(2-bromo-2- methylpropanoyloxymethyl)propanoyl chloride as a yellow oil that was used without further purification. The acid chloride was diluted in a small amount of dry CH2Cl2 (3 mL) and added dropwise to a solution of methyl 6-hydroxy-2-(4-methoxyphenyl)-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate, 1, (906 mg, 2.07 × 10-3 mol), TEA (340 -3 -4 L, 3.42 × 10 mol) and DMAP (13 mg, 1.06 × 10 mol) in dry CH2Cl2 (10 mL) at 0 C and under argon. After stirring for 1 hr at 0 C the temperature was raised to 25 C and the reaction was allowed to reach completion overnight. The solvent was evaporated under vacuum, the residue re-dissolved in diethyl ether (Et2O) (30 mL) and

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washed successively with 0.5M HCl, water, aqueous NaHCO3, water and brine. The organic layer was dried with MgSO4 and the solvent evaporated under vacuum. The product was purified by column chromatography (silica gel 60, Et2O/Hexane) and 1 isolated as light pink coloured crystals (1.40 g, 80%). H NMR (400 MHz, d6-acetone)

: 1.62 (s, 3H, CH3), 1.98 (s, 12H, 4 × CH3), 3.75 (s, 3H, ArOCH3), 3.98 (s, 3H,

COOCH3), 4.62 (q, J 11.3 Hz, 4H, 2 x CH2), 6.49 (d, J 10.0 Hz, 1H, pyran-CH), 6.88- 6.90 (m, 2H, ArH), 6.95 (d, 1H, J 10.0 Hz, pyran-CH), 7.26 - 7.30 (m, 1H, ArH), 7.35 - 7.38 (m, 1H, ArH), 7.46 - 7.48 (m, 2H, ArH), 7.55 - 7.58 (m, 2H, ArH), 7.63 - 7.73 (m, 2H, ArH), 7.88 - 7.90 (m, 1H, ArH), 8.46 - 8.48 (m, 1H, ArH) ppm. 13C NMR (100

MHz, d6-acetone) : 19.0, 31.7, 31.7, 48.7, 54.0, 56.3, 57.8, 67.7, 84.5, 114.9, 115.2, 122.0, 122.4,123.9, 124.1, 127.7, 128.1, 128.5, 129.2, 129.7, 129.7, 129.8, 129.9, 131.0, 138.0, 139.9, 146.6, 147.9, 161.0,167.0, 172.2, 172.2 ppm.

Synthesis of n-butyl 2,2-bis(2-bromo-2-methylpropanoyloxymethyl)propanoate (BBMPP). This compound was synthesized from 2,2-bis(2-bromo-2- methylpropanoyloxymethyl)propanoic acid14-16 and 1-butanol using the same general procedure as above and isolated as a clear oil after purification by column 1 chromatography (silica gel 60, 4:1 CH2Cl2/Hexane) (1g, 67%). H NMR (400 MHz, d6- acetone) : 0.92 (t, J 7.4 Hz, 3H, CH3), 1.35 (s, 3H, CH3), 1.36-1.45 (m, 2H, CH2), 1.61

- 1.68 (m, 2H, CH2), 1.92 (s, 12H, 4 × CH3), 4.15 (t, J 6.5 Hz, 2H, CH2), 4.36 (q, J 11.0 13 Hz, 4H, 2 × CH2) ppm. C NMR (100 MHz, (100 MHz, d6-acetone) : 13.9,18.0, 19.7, 30.9, 31.3, 47.3, 56.9, 65.6, 67.2, 171.2, 172.8, 205.9 ppm.

General procedure for ATRP of n-butyl acrylate with naphthopyran initiator 5. A stock solution containing n-butyl acrylate (8.73 g, 68.10 × 10-3 mol, 5 M), naphthopyran initiator 5 (400 mg, 6.81 × 10-4 mol), dNbpy ligand (556.5 mg, 1.36 × 10-3 mol) was prepared in benzene (3.4 g). 3 mL aliquots were added to ampoules containing CuBr (22.4 mg, 1.56 × 10-4 mol), the final ratio of [n-BA]:[5]:[dNbpy ligand]:[CuBr] was 100:1:2:1. The ampoules were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 2 - 12.8 hrs. The final polymers were purified by (1) evaporation of excess monomer over a gentle stream of

N2 (2) dissolution of the crude mixtures into CH2Cl2 (3) precipitation into methanol (4) decanting of supernatant liquid (5) column chromatography (silica gel 60, 1:1

CH2Cl2/Et2O) to remove residual catalyst (6) removal of solvent under vacuum.

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General procedure for ATRP of n-butyl acrylate with naphthopyran initiator 7. A stock solution containing n-butyl acrylate (9.56 g, 74.58 × 10-3 mol, 5 M), naphthopyran initiator 7 (285.8 mg, 3.73 × 10-4 mol), dNbpy ligand (304.8 mg, 7.46 × 10-4 mol) was prepared in benzene (6.95 g). 3 mL aliquots were added to ampoules containing CuBr (9.4 mg, 6.54 × 10-5 mol), the final ratio of [n-BA]:[7]:[dNbpy ligand]:[CuBr] was 200:1:2:1. The ampoules were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 1.3 - 5.7 hrs. The final polymers were purified as described above.

General procedure for ATRP of n-butyl acrylate with naphthopyran initiator 6. A stock solution containing n-butyl acrylate (8.59 g, 67.04 × 10-3 mol, 4 M), naphthopyran initiator 6 (285.8 mg, 3.35 × 10-4 mol), dNbpy ligand (273.9 mg, 6.70 × 10-4 mol) was prepared in benzene (6.25 g). 3 mL aliquots were added to ampoules containing CuBr (9.4 mg, 6.54 × 10-5 mol), the final ratio of [n-BA]:[6]:[dNbpy ligand]:[CuBr] was 200:1:2:1. The ampoules were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 1 - 3.5 hrs. The final polymers were purified as described above.

ATRP synthesis of p(NP)-co-p(BA) copolymers 13a-13c. A 10 mL stock solution of n-butyl acrylate (5.65 g, 44.1 × 10-3 mol, 98 % by mole), naphthopyran acrylate 11 (443 mg, 9.00 × 10-4 mol, 2 % by mole), ethyl-2-bromo isobutyrate initiator (58.52 mg, 3.00 × 10-4 mol) and dNbpy ligand (245.3 mg, 6.00 × 10-4 mol) was prepared in benzene. 2.5 mL aliquots were added to ampoules containing CuBr (10.8 mg, 7.50 × 10-5 mol), the final ratio of [monomers]:[initiator]:[dNbpy ligand]:[CuBr] in each ampoule was 150:1:2:1. The ampoules were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 1 - 8.2 hrs. The final polymers were purified as above except column chromatography (silica gel 60) was carried out using a gradient column (DCM/Hexane DCM) to remove residual catalyst and unreacted naphthopyran monomer.

ATRP synthesis of p(NP)-co-p(BA) copolymer 14a. A stock solution of n-butyl acrylate (2.25 g, 17.6 × 10-3 mol, 99 % by mole), naphthopyran methacrylate 12 (90 mg, 1.78 × 10-4 mol, 1 % by mole), BBMPP initiator (64.25 mg, 1.32 × 10-4 mol) and dNbpy ligand (107.6 mg, 2.63 × 10-4 mol) was prepared in benzene (1.25 g). This solution was transferred to an ampoule containing CuBr (18.9 mg, 1.32 × 10-4 mol), the final ratio of

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[monomers]:[initiator]:[dNbpy ligand]:[CuBr] in each ampoule was 135:1:2:1. The ampoules were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 2 hrs. The final polymer was purified by

(1) evaporation of excess monomer over a gentle stream of N2 (2) dissolution of the crude mixtures into CH2Cl2 (3) precipitation into methanol (4) decanting of supernatant liquid (5) column chromatography (silica gel 60, 1:1 CH2Cl2/Et2O) to remove residual catalyst and (6) removal of solvent under vacuum.

ATRP Synthesis of Triblock copolymer 15a, NP-[p(BA)25-b-p(IBA)54]2 A stock solution containing n-butyl acrylate (1.55 g, 12.08 × 10-3 mol, 4 M), naphthopyran initiator 6 (103 mg, 1.21 × 10-4 mol), dNbpy ligand (98.7 mg, 2.42 × 10-4 mol) was prepared in benzene (1.13 g) and added to an ampoule containing CuBr (17.3 mg, 1.21 × 10-4 mol), the final ratio of [n-BA]:[6]:[ligand]:[CuBr] was 100:1:2:1. The ampoule was degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 1 hr. The final polymer was purified by (1) evaporation of excess monomer over a gentle stream of N2 (2) dissolution of the crude mixtures into

CH2Cl2 (3) precipitation into methanol (4) decanting of supernatant liquid (5) column chromatography (silica gel 60, 1:1 CH2Cl2/Et2O) to remove residual catalyst and (6) removal of solvent under vacuum. Block extension was carried out by making a solution of the purified p(BA) macroinitiator (654 mg, 9.16 × 10-5 mol), IBA (2.86 g, 13.74 × 10-3 mol, 3.2 M), dNbpy ligand (74.9 mg, 1.83 × 10-4 mol) in benzene (1.22g) and adding this to an ampoule containing CuBr (13.1 mg, 9.16 × 10-5 mol), the final ratio of [monomer]/[CuBr]/[dNbpy]/[macroinitiator] = 154:1:2:1; The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 4 hrs 10 mins. The final polymers were purified by (1) dissolution of the crude mixtures into CH2Cl2 (2) precipitation into methanol (3) decanting of supernatant liquid (4) column chromatography (silica gel 60, 1:1

CH2Cl2/Et2O) to remove residual catalyst and (5) removal of solvent under vacuum.

ATRP Synthesis of Triblock copolymer 15b, NP-[p(BA)35-b-p(IBA)65]2 A stock solution containing n-butyl acrylate (4.03 g, 31.40 × 10-3 mol, 4 M), naphthopyran initiator 6 (134 mg, 1.57 × 10-4 mol), dNbpy ligand (128 mg, 3.14 × 10-4 mol) was prepared in benzene (2.93 g). A 3 g aliquot was added to an ampoule containing CuBr (9.37 mg, 6.53 × 10-5 mol), the final ratio of [n-BA]:[6]:[dNbpy ligand]:[CuBr] was 200:1:2:1. The ampoule was degassed with three freeze-pump-thaw cycles, sealed and

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then heated at 90 °C in a thermostatted oil bath for 1 hr 20 mins. The final polymer was purified by (1) evaporation of excess monomer over a gentle stream of N2 (2) dissolution of the crude mixtures into CH2Cl2 (3) precipitation into methanol (4) decanting of supernatant liquid (5) column chromatography (silica gel 60, 1:1

CH2Cl2/Et2O) to remove residual catalyst and (6) removal of solvent under vacuum. Block extension was carried out by making a solution of the purified p(BA) macroinitiator (460 mg, 4.76 × 10-5 mol), IBA (1.49 g, 7.14 × 10-3 mol, 3.2 M), dNbpy ligand (38.9 mg, 9.52 × 10-5 mol) in benzene (0.63 g) and adding this to an ampoule containing CuBr (6.83 mg, 4.76 × 10-5 mol), the final ratio of [monomer]/[CuBr]/[dNbpy ligand]/[macroinitiator] = 150:1:2:1; The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 4 hrs 10 mins. The final polymers were purified by (1) dissolution of the crude mixtures into CH2Cl2 (2) precipitation into methanol (3) decanting of supernatant liquid (4) column chromatography (silica gel 60, 1:1

CH2Cl2/Et2O) to remove residual catalyst and (5) removal of solvent under vacuum.

ATRP Synthesis of Triblock copolymer 15c, NP-[p(BA)60-b-p(IBA)30]2 A stock solution containing n-butyl acrylate (4.03 g, 31.40 × 10-3 mol, 4 M), naphthopyran initiator 6 (134 mg, 1.57 × 10-4 mol), dNbpy ligand (128 mg, 3.14 × 10-4 mol) was prepared in benzene (2.93 g). A 3 g aliquot was added to an ampoule containing CuBr (9.37 mg, 6.53 × 10-5 mol), the final molar ratio of [n-BA]:[6]:[ligand]:[CuBr] was 200:1:2:1. The ampoule was degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 2 hrs 50 mins. The final polymer was purified by (1) evaporation of excess monomer over a gentle stream of N2 (2) dissolution of the crude mixtures into CH2Cl2 (3) precipitation into methanol (4) decanting of supernatant liquid (5) column chromatography (silica gel 60, 1:1

CH2Cl2/Et2O) to remove residual catalyst and (6) removal of solvent under vacuum. Block extension was carried out by making a solution of the purified p(BA) macroinitiator (672 mg, 4.10 × 10-5 mol), IBA (1.28 g, 6.15 × 10-3 mol, 3.2 M), dNbpy ligand (33.5 mg, 8.20 × 10-5 mol) in benzene (0.85 g) and adding this to an ampoule containing CuBr (5.88 mg, 4.10 ×10-5 mol), the final ratio of [monomer]/[CuBr]/[dNbpy ligand]/[macroinitiator] = 144:1:2:1; The ampoule was then degassed with three freeze- pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 4 hrs 10 mins . The final polymers were purified by (1) dissolution of the crude mixtures into

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CH2Cl2 (2) precipitation into methanol (3) decanting of supernatant liquid (4) column chromatography (silica gel 60, 1:1 CH2Cl2/Et2O) to remove residual catalyst and (5) removal of solvent under vacuum.

ATRP Synthesis of Triblock copolymer 16a, (n-butyl)-[(p(NP)0.01-co-p(BA)0.99)58-b- -5 p(IBA)28]2. A solution of macroinitiator 14a (681 mg, 3.98 × 10 mol), IBA (1.24 g, 5.97 × 10-3 mol, 3.2 M), dNbpy ligand (32.51 mg, 7.96 × 10-5 mol) in benzene (0.53 g) was added to an ampoule containing CuBr (5.71 mg, 3.98 × 10-5 mol), the final ratio of [monomer]/[CuBr]/[dNbpy ligand]/[macroinitiator] = 150:1:2:1; The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 90 °C in a thermostatted oil bath for 4 hrs 10 mins. The final polymers were purified by (1) dissolution of the crude mixtures into CH2Cl2 (2) precipitation into methanol (3) decanting of supernatant liquid (4) column chromatography (silica gel 60, 1:1

CH2Cl2/Et2O) to remove residual catalyst and (5) removal of solvent under vacuum.

Preparation of Photochromic Lens Samples. The naphthopyran-p(BA) conjugates (or controls) were individually dissolved in a standard industrial lens formulation made up of 1:4 weight ratio of poly(ethylene glycol) (400) dimethacrylate and 2,2’-bis((4- methacryloxyethoxy)phenyl)propane (Figure 14) with 0.4 % by mass of AIBN. The samples were then cured at 80 C for 16 hrs in a mold to give optically clear test samples of equivalent thickness (~ 2.4 mm). They were each doped at equivalent concentrations of 1.5 × 10-7 mol/g (mole of polymer-dye conjugate per gram of lens formulation). This concentration was chosen so that optical densities could be maintained within a range that was meaningful for the detector.

Preparation of Photochromic Films. Block Copolymers were dissolved in toluene (~0.3 M) and then cast onto glass slides. The films were left to dry at room temperature for 8 hrs and then dried and annealed in a vacuum oven at 100 ºC overnight.

Figure 14. Structures of monomers in thermally curable host matrix formulation.

131 Chapter 4. The Importance of Macromolecular Architecture… ______

4.5 References

(1). Naour-Sene, L. L. Process of intergrating a photochromic substance into an opthalmic lens and a photochromic lens of organic material. US 4,286,957, 1981. (2). Maltman, W. R.; Threlfall, I. M. Process for manufacturing photochromic articles. US 4,851,471, 1989. (3). Ercole, F.; Davis, T. P.; Evans, R. A. Macromolecules 2009, 42, 1500-1511. (4). Evans, R. A.; Such, G. K.; Malic, N.; Davis, T. P.; Lewis, D. A.; Campbell, J. A. Photochromic Compounds Comprising Polymeric Substituents and Methods for Preparation and Use Thereof.WO2006024099, 2006. (5). Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Davis, T. P.; Such, G. K.; Yee, L.H.; Ball,G.E.; Lewis, D. A. Nat. Mater. 2005, 4, 249-254. (6). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2004, 37, 9664-9666. (7). Such, G. K.; Evans, R. A.; Davis, T. P. Mol. Cryst. Liq. Cryst. 2005, 430, 273- 279. (8). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2006, 39, 1392-1396. (9). Malic, N.; Campbell, J. A.; Evans, R. A. Macromolecules 2008, 41, 1206- 1214. (10). Malic, N.; Evans, R. A. Aust. J. Chem. 2006, 59, 763-771. (11). Kumar, A.; VanGemert, B.; Knowles, D. B. Novel substituted naphthopyrans. WO 95/16215, 1995. (12). Ercole, F.; Malic, N.; Davis, T. P.; Evans, R. A. J. Mater. Chem. 2009, 19, 5612-5623. (13). Ihre, H.; Hult, A.; Soderlind, E. J. Am. Chem. Soc. 1996, 118, 6388-6395. (14). Shi, Y.; Fu, Z.; Li, B.; Zhang, L.; Cai, X.; Zhang, D. Eur. Polym. J. 2007, 43, 2612-2619. (15). Liu, Q.; Zhao, P.; Chen, Y. J. Polym. Sci., A 2007, 45, 3330-3341. (16). Heise, A.; Nguyen, C.; Malek, R.; Hedrick, J. L.; Frank, C. W.; Miller, R. D. Macromolecules 2000, 33, 2346-2354. (17). Postma, A.; Davis, T. P.; Li, G. X.; Moad, G.; O’Shea, M. S. Macromolecules 2006, 39, 5307-5318. (18). Hakim, M.; Verhoeven, V.; McManus, N. T.; Dube , M. A.; Penlidis, A. J. App. Polym. Sci. 2000, 77 (3), 602-609.

132 Chapter 4. The Importance of Macromolecular Architecture… ______

(19). Delbaere, S.; Luccioni-Huoze, B.; Bochu, C.; Teral, Y.; Campredon, M.; Vermeersch, G. J. Chem. Soc., Perkin Trans. 2. 1998, 1153-1157. (20). Biteau, J.; Chaput, F.; Boilot, J. J. Phys. Chem. 1996, 100, 9024-9031. (21). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2006, 39, 9562-9570. (22). Sriprom, W.; Neel, M.; Gabbutt, C. D.; Heron, M.; Perrier, S. J. Mater. Chem. 2007, 17, 1885-1893. (23). Dervaux, B.; Van Camp, W.; Van Renterghem, L.; Du Prez, F. E. J. Polym. Sci., A 2008, 46, 1649-1661. (24). Beuermann, S.; Paquet, D. A., Jr.; Mc Minn, J. H.; Hutchinson, R. A. Macromolecules 1996, 29, 4206-4215.

133 5 Optimizing the Photochromic Performance of Naphthopyrans in a Rigid Host Matrix using Poly(dimethylsiloxane) Conjugation.

5.1 Introduction

The optical lens market continues to be the largest consumer of photochromic dyes in which subsituted 2,2-diaryl-2H-naphtho[1,2-b]pyrans, with the base structure shown in Scheme 1, are highly represented.1-4 Chemical developments aimed at improving performance characteristics of these dyes, such as intensity of colouration, fade rate, fatigue resistance and photogenerated colour have been extensive. For example: 5- alkoxycarbonyl substitution5; heterocyclic fused moieties (e.g. an indeno group) 6, 7; judiciously positioned electron donating substituents (e.g. methoxy or dialkyl amino) 8 and concurrent steric affects of substituents have all been found to influence photochromic characteristics such as de/colouration rates and photogenerated colour.9

Scheme 1. Generic photochromic transition of a substituted 2,2-diaryl-2H- naphtho[1,2-b]pyrans.

The photochemical as well as the thermal behaviour of the photochromic molecules are also profoundly influenced by the media in which they are incorporated into. As discussed in previous chapters, photochromic switching involves substantial mechanical movement since atleast one intramolecular rotation is required for colouration and decolouration. Therefore, in solid media the molecules are restricted in their movement which makes their switching speed significantly slower than in solution.10 The application of polymer conjugation to photochromic dyes as a way to control and improve their behaviour within a host can be achieved using controlled radical polymerization techiniques.11-14 An adjunct approach which is presented Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______here, is to directly conjugate the dye to a pre-formed polymer. The attachment of PDMS (poly(dimethylsiloxane)) oligomers has been found to elicit a significant influence to the dye’s performance.14 PDMS tailing provides the dye a local environment of low viscosity and higher mobility within the lens matrix tp effectively improving its switching ability. The purpose of the work presented in this chapter was to exploit PDMS conjugation and investigate its capacity to influence the photochromic behaviour within a rigid host matrix, for a variety of known methoxy substituted 2,2-diaryl-2H- naphtho[1,2-b]pyrans. An OH group on the naphthopyran was used as the tethering point with subsequent conjugation via condensation chemistry. Practical strategies for synthesizing and accessing appropriate starting materials and conjugates were also presented. Photochromic spectrokinetic properties of PDMS conjugated dyes within the host matrix (compostion shown in Figure 1) were compared to those of electronically equivalent control dyes which lacked PDMS tailing. The extent of solution-like performance provided in the host matrix by PDMS conjugation was investigated by comparing their fade performance with that of control dyes in solution.

Figure 1. Industrial lens formulation composed of poly(ethylene glycol) (400) dimethacrylate (PEGMA) and 2,2’-bis((4-methacryloxyethoxy)phenyl)propane (EBPDMA) (1:4) with 0.4% by mass of AIBN. 5.2 Results and Discussion

5.2.1 Naphthopyrans

Substituted 2,2-diaryl-2H-naphtho[1,2-b]pyrans (NP) are synthesized by reacting a 1-naphthol (N), with a diaryl prop-2-yn-1-ol (P) in the presence of an acidic catalyst (Scheme 2). The formation of the naphthopyran is confirmed by the appearance of characteristic resonances in the 1H NMR spectrum between 6 and 8 ppm with coupling constants of J 10 Hz from pyran ring protons H-3 and H-4. The mechanisms involved in formation are well known, involving the Claisen 136 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______rearrangement of the generated naphthyl propargyl ether.15 The reaction can be carried out in a solvent (e.g. toluene) or in solid state (grinding reagents in silica gel), with varying degrees of acid strength of catalyst (e.g. p-toluene sulfonic acid or refluxing in acidic alumina) or with the addition of a dehydrating agent to react with the generated water (trimethyl orthoformate).16,17 It has been shown previously that the substitution patterns can dramatically influence photogenerated colour and switching speed by effecting the stability of the generated ring-opened forms, as investigated by Gabbut et.al.8,18 Alkoxycarbonyl substitution at position 5 assists fade rate; 9-methoxy substitution results in a faster fade rate compared to 6-methoxy substitution due to large disparities in the stability of their open forms; bis vs. mono p-methoxy substitution on the diaryl portion of the naphthopyran increases the fade rate and bathochromically shifts the absorption of the coloured form.8,19,20 An extra 6-phenyl moeity subsituted on the already bulky naphthol ring also poses further steric considerations. Finally, an indeno moiety joining positions 5 and 6 is another significant structural modification of the 2,2- diaryl-2H-naphtho[1,2-b]pyrans.6,7,21 Along with p-methoxy substitution on the diaryl rings, such naphthopyrans produce open forms containing an extended - electron system that are significantly shifted to higher wavelegnths and capable of displaying faster bleaching kinetics. The naphthopyran dyes exploited in this study were chosen to display a broad range of switching speeds both in solution and in a host matrix by variation of these known substitution patterns. The preliminary requirement of this work was therefore the synthesis of such naphthopyrans incorporating a free hydroxyl group for subsequent attachment of PDMS oligomers. Overall, the conditions for final assembly of the dyes were optimized in order to achieve synthesis yields comparable to those found in literature for equivalent non-hydroxyl functionalized dyes (30- 70%). Hydroxyl functionalized naphthopyrans 16 - 21, listed in Table 1, were assembled from relavent starting materials and then converted to their corresponding ester derivatives which are displayed collectively as Figure 3. The naphthopyrans (NP) each contain 5-alkoxycarbonyl substitution shown in the base structure in Scheme 2. Hydroxyl indeno-fused naphthopyran, 22, shown in Figure 2, was also synthesized accordingly and converted to its esterifed derivatives also displayed in Figure 3.

137 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Table 1. Substituted hydroxyl naphthopyrans (NP) synthesized from corresponding reactants, naphthol (N) and propynol (P).

Naphthopyrans Reactants Naphthopyran Substituents a

NP N P -R1 -R2 -R3 -R4

16 2a 14 OCH3 OCH3 CH3 6-OH

17 2a 15 OCH3 H CH3 6-OH

18 2b 13 OCH3 OCH2CH2CH2OH CH3 6-OCH3

19 6b 14 OCH3 OCH3 CH2CH2CH2OH 9-OCH3

20 6b 15 OCH3 H CH2CH2CH2OH 9-OCH3

21 8 14 OCH3 OCH3 CH2CH2OH 6-Ph a (R1-R4 refer to NP in Scheme 2)

Scheme 2. Synthesis of naphthopyran from substituted starting materials.

138 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Figure 2. Substituted Hydroxyl Indeno Fused Naphthopyran 22 synthesized from propynol 14 and naphthol 10.

5.2.2 Starting Materials

5.2.2.1 Naphthols

Methyl 1,4-dihydroxy-2-naphthoate, 2a (Scheme 3), was prepared from commercially available 1,4-dihydroxy-2-naphthoic acid, 1.22 Carboxyl substitution present in the 2a precludes the formation of possible di-naphthopyran species, affording naphthopyrans substituted with a free 6-hydroxy group.9 Such by-products can be produced in significant proportion from dihydroxy naphthalenes due to the prescence of two reactive centres.

Scheme 3. 2a (i) MeI, DMF, NaHCO3 (1 equiv.), 100 C ; 2b (ii) K2CO3 (4 equiv.), H2O / i-PrOH (5:1), propionyl chloride (1.5 equiv.), -15 C, neutralization (iii) K2CO3 (4 equiv.), dry acetone, MeI (8 equiv.) (iv) K2CO3 (1.5 equiv.), MeOH.

The 6-hydroxy moiety present in, for example, naphthopyrans 16 and 17, can then be methylated as a way to access a 6-methoxy substitution. However, this direct conversion also affords a major ring-opened and non-photochromic by- product, as reported by Gabbut et al.18 I therefore explored an alternative strategy via the assembly of the appropriate starting material, methyl 4-hydroxy-1-methoxy- 2-naphthoate (2b), using the series of transformations as shown in Scheme 3.

139 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Reaction of in cold and basic water-isopropanol solution, with one and a half equivalents of propionyl chloride selectively acylated the phenol, affording 1- hydroxy-4-(propionyloxy)-2-naphthoic acid in 75% crude yield (with 25% of starting material 1 remaining present). The crude mixture was alkylated with an excess of methyl iodide and K2CO3 in dry acetone to give methyl 1-methoxy-4- (propionyloxy)-2-naphthoate in the same proportions, followed by the removal of the propionyl group using an alcoholic solution of K2CO3. Importantly, 2b could then be isolated from the crude organic mixture by selective extraction using 0.1M NaOH, with an overall isolatable yield of 70% from 1. 4-Hydroxy-6-methoxy-2-naphthoic acid 5 was required for the synthesis of 6a and 6b. As shown in Scheme 4, the strategy used to assemble 5 firstly involved the Stobbe condensation of 4-methoxy benzaldehyde with a diethyl succinate (using NaOEt / t-BuOK)18,23-25 to produce the required half-ester 3a. The crude yield of this reaction was consistently 70% and comparable to literature values. A pale yellow precipitate, however, formed on standing from the amber viscous oil (~ 13% by mass) and found to be an isomeric mixture (both E/E and Z/Z isomers) of 3b, forming as a result of a second molecule of benzaldehyde condensing the generated half ester, 3a. The use of anhydrous ethanol gave a cleaner product18 with no by- product evident by 1H NMR, but I found yields to be disappointing (35%). Removal of the by-product was easily carried out via filtration, being insoluble in most solvents, however, the use of solvent-free conditions26 provided us with the half ester in higher yields and exclusive of 3b. Friedel-Crafts acylation of the resulting crude half ester, 3a, gave the cyclised product 4, followed by base hydrolysis to afford 5.

Scheme 4. (i) Diethyl succinate, Na ethylate (2 equiv.), reflux (ii) anhydrous NaOAc (1.1 equiv.), acetic anhydride (iii) 5 % NaOH in EtOH/H2O (4:1).

140 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

1-Phenyl substituted naphthoic acid, 7, was also synthesized from benzophenone using Stobbe condensation chemistry though no analogous by-product was ever formed during its synthesis. Condensation of a large excess of a diol, such as ethylene glycol, with the generated substituted naphthoic acids (5 and 7) was a logical approach to introduce hydroxyl functionality to naphthol derivatives.27 Esterification with methanol using Fischer esterification conditions (high excesses of methanol and catalytic quantities of acid) was straight forward, quantitatively generating the methyl ester derivative, 6a (Scheme 5). However, numerous attempts to condense ethylene glycol to 5 in the equivalent manner proved futile, with numerous etherified and inseparable by- products formed during the reaction. Lower temperatures only resulted in low conversion to products. A more successful strategy was found to be the nucleophilic displacement of a halogen by the selectively deprotonated naphthoic acid. With one equivalent of NaHCO3 and dry DMF, two equivalents of 3-chloropropanol and sodium iodide, 6b could be synthesized in 65% yield and with exceptional purity (Scheme 5). The use of 2-bromoethanol proved even more successful giving yields in excess of 90% for 8 (Scheme 6).

Scheme 5. (i) MeOH, H2SO4 (catalytic) (ii) 3-chloropropanol (2 equiv.), NaI (2 equiv.), dry DMF, NaHCO3 (1 equiv.), 100C.

Friedel Crafts cyclization28 of 7, followed by the reduction of the carbonyl group29 of the resultant fluorenone derivative, 9, gave the hydroxyl substituted benzofluorenol 10, as shown in Scheme 6.

141 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Scheme 6. (i) Stobbe Condensation with dimethyl succinate, Friedel Crafts acylation, base hydrolysis (ii) 2-bromoethanol (2 equiv.), dry DMF, NaHCO3 (1 equiv.), 100 C (iii) methanesulfonic acid, 60 °C (iv) NaBH4, wet THF 50 °C. 5.2.2.2 Propynols

Diaryl prop-2-yn-1-ols can be conveniently prepared by the addition of lithium trimethylsilylacetylide to a benzophenone following removal of the trimethylsilyl group.15,30 In this work 13 and 14 were easily accessed from commercially available benzophenones. Hydroxyl substitution can also be introduced to the naphthopyran via the diaryl prop-2-yn-1-ol,31,32 as exemplified with naphthopyran 18. Williamson etherification of 11 with 3-chloropropanol generated 12 which was then converted to diaryl propynol 13 (Scheme 7). However, attempts to generate a propynol directly from the phenolic benzopehenone 11 were unsuccessful. Meyer-Schuster rearrangement of the propynol,30,33 resulted in its degradation and the material formed an intractable gum on standing. The generation of propynol 13 from 12 was therefore the preferable option for our investigations.

Scheme 7. (i) 3-chloropropanol (2 equiv.), NaI (2 equiv.), DMF, K2CO3 (2 equiv.), 100 C. (ii) lithium trimethylsilylacetylide, anhyd. THF, 0 C to RT (iii) KOH, MeOH, then AcOH.

142 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Figure 3. Molecular glossary of substituted naphthopyrans tested. 143 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

5.2.2.3 Conjugated Naphthopyrans

The condensation of naphthopyrans 16-22 to their corresponding ester derivatives was carried out using standard acid chloride chemistry, as shown in Scheme 8. Carboxylic acid terminated PDMS was prepared from commercially available OH terminated PDMS by acylation with succinic anhydride. The oligomeric product was shown by 1H NMR to have an average molecular weight of approx. 1,200 g/mol where n= ~13. Esterification reactions generated both PDMS conjugates (16b-22b) and propionate control naphthopyrans (16a-22a) in high yields, with products easily purified by chromatography. The final substituted naphthopyrans (both propionate controls and PDMS conjugates) and control dyes 18c, 19c and 20c are displayed in a glossary as Figure 3.

Scheme 8. Condensation chemistry for synthesizing propionate naphthopyran controls (16a-22a) and PDMS naphthopyran conjugates (16b-22b); (i) succinic anhydride, TEA, DCM, rt (ii) (COCl)2, DCM, DMF (1 drop), rt (iii) DCM, TEA, rt. See experimental for n values (normally n = ~ 13).

Each PDMS conjugate produced displayed a high level of purity; every methylene proton was accounted for, correct integral ratios and expected peak shifts associated with ester bond formation were exhibited (refer to Experimental for all 1H NMR assignments and final n values for PDMS conjugated tail (normally = ~13). An example 1H NMR spectrum for PDMS conjugate 19b with final peak assignments is shown below (Figure 4).

144 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

1 Figure 4. H NMR spectrum (d6-acetone) of PDMS conjugate 19b with peak assignments. * HDO, H2O (2.84 ppm) and acetone (2.05 ppm).

The final photochromic test samples were prepared by dissolving the photochromic conjugates and controls individually in a lens monomer formulation. Previous 2D NMR investigations have confirmed intramolecular and localized associations between PDMS oligomer chains and covalently bound spirooxazine photochromic dyes in solution.14 Within the environment of a rigid matrix stronger interactions are envisaged due to the reduced miscibility and chemical compatibility of the PDMS with the host matrix. The partitioning of oligomer tails around bound dye moieties is believed to provide an overall insulation and encapsulation effect. Visibly obvious hazing in the cured lens sample, as a result of undesirable phase separation of PDMS-dye conjugates, was not observed throughout my sample preparation. This indicated an appropriate level of miscibility of the PDMS with the lens host with the concentration levels used (Table 2).

5.2.3 Photochromic Properties

When irradiated with UV light an initially colourless photochromic test sample becomes highly coloured. Upon cessation of the incident UV light, the thermal back reaction occurs as the napthopyran open form undergoes ring closure and samples

145 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______decolourize spontaneously in the dark. Spectrokinetic properties are studied by monitoring absorption density with time at the max of the coloured form. Firstly the sample is continuously irradiated for 1000 seconds and then the decolouration kinetics of the naphthopyrans in solution and in the host matrix is investigated in the dark at 20 °C upon cessation of UV irradiation. The following empirical biexponential equation34,35 was used to anlayze the thermal ring closure kinetics within the host matrix :    k1t  k2t  A(t) A1e A2e Ath where A(t) is the optical density at max of the open form; A1 and A2 are the contributions to the initial optical density A0; k1 and k2 are exponential decay rate constants of fast and slow components respectively and Ath is the residual colouration (offset).

The other standard photochromic parameters presented were the max of the photocoloured form and colourability, A0 which is the absorbance level achieved after 1000 seconds of continuous irradiation. This equation has been used frequently to represent and compare the decolouration behaviour of both spirooxazines and naphthopyrans within solid media31,34-37 and has consistently fitted our decolouration 38-41 curves with correlation coefficients (R) greater that 0.99. An evaluation of T1/2 values, which is the time taken for the sample to fade to half of initial absorbance value, is also insightful for comparing overall kinetics. As depicted in Scheme 1 exposure of the naphthopyran closed form (CF) to continuous UV irradiation results in a distribution of coloured merocyanine isomers. Spectroscopy studies have underlined the formation of two main classes of transoid open isomers: a short-lived and major component, namely trans-cis (TC) geometrical isomers and a longer-lived and minor trans-trans (TT) population. The latter reverts to the closed form through a two step process (TT TC CF), with the TC isomers being the intermediates (see Figure 1 in Appendix 3). The thermal decolouration behaviour in solution can be attributed to these two main classes of 35,42-44 open isomers decaying with different first-order rate constants, k1 and k2. Kinetics within a solid substrate can be complicated by a more disperse environment in terms of distributions of free volume and variations in chemical composition within the matrix environment. Therefore, separated constants k1 and k2, in the equation above, along with their allocated contributions to initial optical

146 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______density, are overall empirical values representing only fast and slow components. It is noteworthy, however, that PDMS conjugates tested in this study displayed a diminished contribution term, A2 which is associated with the slower kinetic component k2, compared to their control samples. Their kinetics more closely approached the simplified decays displayed by naphthopyrans in solution. I believe that this trend is indicative of a more homogenous and less disperse local environment created for naphthopyran molecules within the matrix as a result of PDMS tailing. Table 2 summarizes the data obtained for kinetic fitting for all samples tested. For visual convenience, data for the PDMS conjugates are listed between that of the controls in solution (which are fastest and at the bottom of each set) and that of the controls in the host matrix (which are slowest and at the top of each set). On the whole, all naphthopyran dyes tested displayed accelerated switching speeds in the host matrix (both colouration and decolouration) when conjugated to

PDMS compared to their controls. This was evidenced by reduced T1/2 values and increasing rate constants throughout (see Table 2); T1/2 values were 1.3 to 4.7 times lower (reduced by 42-80%) and fast rate constants, k1, were 1.2 to 2.8 times greater for PDMS conjugates compared to their non-conjugated controls. This is particularly apparent in Figure 5 which shows the overlaid colouration and decolouration curves for indeno-fused naphthopyrans 22a and 22b.

Figure 5. Normalised Absorbance vs.Time for the colouration and decolouration of indeno-fused naphthopyran control dye 22a and corresponding PDMS conjugate 22b in a rigid polymeric host matrix PEGDMA:EBPDMA (1:4).

147 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Table 2. Photokinetic Analysis of the Decolouration of Control and PDMS conjugated Naphthopyrans in host lens matrix (PEGMA:EBPDMA,1:4 m/m) vs. Control Naphthopyrans in Toluene. a

k k Host d A b A 1 A 2 A T (s)c max 0 1 (min-1) 2 (min-1) th 1/2 (conc.)e (nm) 16a 1.22 0.69 1.209 0.13 0.077 0.16 55 s lens (6 × 10-7) 510 16b 1.35 0.80 1.837 0.06 0.096 0.14 31 s lens (6 × 10-7) 510 16a 1.85 0.82 3.691 0.20 0.039 0.04 19 s toluene (9.5 × 10-3) 499 17a 0.91 0.64 0.638 0.10 0.072 0.24 120 s lens (1.5 × 10-7) 500 17b 1.10 0.72 1.034 0.04 0.103 0.23 63 s lens (1.5 × 10-7) 500 17a 1.42 0.69 1.036 0.24 0.005 0 52 s toluene (5.0 × 10-5) 485 18c 1.24 0.60 0.401 0.13 0.072 0.26 212 s lens (1.5 × 10-7) 511 18a 1.15 0.64 0.463 0.10 0.077 0.24 167 s lens (1.5 × 10-7) 511 18b 1.23 0.70 0.567 0.06 0.110 0.24 123 s lens(1.5 × 10-7) 511 18c 0.84 0.70 0.724 0.18 0.025 0.05 74 s toluene (3.0 × 10-5) 501 19c 1.45 0.68 3.197 0.12 0.072 0.17 20 s lens (1.2 × 10-6) 519 19a 1.12 0.71 4.038 0.11 0.077 0.16 15 s lens (1.2 × 10-6) 519 19b 1.24 0.88 8.852 0.03 0.040 0.14 6 s lens (1.2 × 10-6) 519 19c 0.49 0.98 12.622 0.08 0.782 0 4 s toluene (2.0 × 10-4) 508 20c 1.98 0.70 2.186 0.08 0.072 0.19 28 s lens (1.2 × 10-6) 507 20a 1.79 0.73 2.878 0.08 0.075 0.18 26 s lens (1.2 × 10-6) 507 20b 1.09 0.85 4.928 0.03 0.024 0.16 11 s lens (1.2 × 10-6) 507 20c 0.87 0.89 5.479 0.13 0.041 0.01 10 s toluene (6.4 × 10-5) 497 21a 0.62 0.51 0.853 0.20 0.064 0.24 129 s lens (1.5 × 10-7) 515 21b 0.83 0.62 1.228 0.15 0.082 0.20 60 s lens (1.5 × 10-7) 515 21a 1.19 0.94 5.247 0.13 0.662 0.01 11 s toluene (6.5 × 10-5) 507 22a 0.53 0.43 0.390 0.31 0.047 0.21 355 s lens (1.5 × 10-7) 560 22b 0.73 0.71 0.776 0.16 0.083 0.10 76 s lens (1.5 × 10-7) 560 22a 1.01 0.82 1.052 0.15 0.138 0.001 45 s toluene (4.7 × 10-5) 553 a Samples initially irradiated at 350-400 nm for 1000 seconds, then thermal decolouration monitored at max of the coloured form (determined by wavelength scan of coloured formd) at 20 °C in the dark for 4800 seconds. b Measured absorbance intensity at onset of thermal decolouration period. c Time taken for the initial absorbance e value A0 to decay to half concentration in mol (naphthopyran) /gram matrix formulation (for lens); M (in toluene).

148 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

A comparison of the kinetics of naphthopyran controls 18c, 19c and 20c with respect to their alkyl extended and electronically equivalent versions (18a, 19a and 20a) showed some additional improvement to rates with an additional spacer (1.1-

1.3 times higher T1/2 values for controls containing extra spacer). However, this effect was insignificant compared to that displayed by PDMS conjugation. Figure 6 shows the overall improvement to the switching kinetics displayed by PDMS- conjugated 19b compared to the slower controls 19a and 19c, the latter displaying only minor differences with respect to one another.

Figure 6. Normalised Absorbance vs. Time for the colouration and decolouration of 9-methoxy substituted naphthopyran control dyes 19a and 19c compared to corresponding PDMS conjugate 19b in a rigid polymeric host matrix PEGDMA:EBPDMA (1:4).

All naphthopyran controls showed slower kinetics in the matrix compared to their solution behaviour. This is expected due to the restricted rotational mobility of the photochromic molecules in the rigid host. The major fast decay constant, k1, for 6-phenyl substituted naphthopyran control 21a, dropped to a sixth of the value in the matrix compared to solution, evidenced also by significantly different T1/2 values (129 s for matrix compared to 11 s for solution). Indeno fused 22a also showed considerably slower switching speed in the matrix (T1/2 355 s) compared to its behaviour in solution (T1/2 45 s). The extent to which PDMS conjugation offers solution-like behaviour was estimated by directly comparing the T1/2 values of the PDMS conjugate in the matrix to those

149 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______of the control in solution (set as the lowest limit). Overall this measure ranged from 20% for 21b to 90% for 20b with conjugates 17b, 19b, 20b and 22b being particularly impressive. Several factors are likely to be involved; the 6-phenyl substituted naphthopyran 21a is more likely to experience steric hindrance to bond rotation within the matrix due to an additional aromatic moiety whereas naphthopyran dyes 19c and 20c have the benefit of a 9-methoxy moiety which acts to positively influence the energetics of the system for ring closure.18 Interestingly the indeno-fused naphthopyran 22b, also containing an extra bulky heterocyclic moiety, showed superior performance by more closely approaching its solution-like behaviour in the matrix, in contrast to 21b. Figure 7 also displays superior performance for the colouration and decolouration behaviour of PDMS dye 17b in the host matrix compared to the control 17a and its ability to restore solution like kinetics. Inspection of the overlaid curves also indicates a weak yet residual colouration in the matrix which could only be removed in a reasonable period of time on exposure to visible light. In solution however, this eventually faded completely in the dark. This was also evident in all other samples tested and is likely to be due to stable isomer populations whose conversion back to their closed forms is particularly unfavourable within the matrix, even in the presence of a lubricating tail.

Figure 7. Normalised Absorbance vs. Time for the colouration and decolouration of naphthopyran control dye 17a and corresponding PDMS conjugate 17b in host matrix PEGDMA:EBPDMA (1:4), 1.50  10-7 mol/g, compared to the behaviour of 17a in toluene (5.0 × 10-5 M).

150 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Attachment of PDMS does not aim to modulate photochromic speed by manipulating electronic characteristics of the naphthopyran; it simply aims to restore the dye’s switching potential when incorporated into a rigid media. Therefore, the methodology cannot make an inherently slow dye become fast and certainly not faster than its solution speed at a given temperature. For example, PDMS conjugated dye 18b, containing a 6-methoxy moiety, could never achieve the decolouration speeds in the matrix that are displayed by 9-methoxy substituted control dyes 19c and 20c, despite the presence of a lubricating tail - its electronic nature renders the dye inherently slow. Therefore, the overall speed of the PDMS naphthopyran dye conjugate within the host is determined by many interplaying factors: the thermodynamics of the photochromic transition, influenced by electronic substitution, simultaneous steric affects, as well as the overall rigidity imposed by the local environment. I therefore do not expect the impact on kinetics offered by PDMS conjugation to be the same for each dye. In previous investigations, the attachment of low Tg radically-polymerized tails such as poly(n-butyl acrylate) to naphthopyran dyes of base structure 16a and 17a, displayed not only improved de/colouration speeds but also enhanced optical densities (colourabilities) compared to their unconjugated controls.39,45 These concurrent fast and dark effects were not evidenced throughout our entire investigations. Whilst a larger proportion of PMDS-naphthopyrans tested did display higher colourabilties some showed the contrary, such as the 9-methoxy substituted PDMS conjugates (19b and 20b). It is well known that the photocolouration period involves both thermal and photochemical pathways inter-converting between the isomers.35,42,43 A diminished colourability is likely to be the result of competitive thermal reverse processes which can affect the amount of colourless form able to convert during irradiation.46 Nonetheless, all colouration curves comprehensively displayed an overall positive effect from PDMS conjugation with samples achieving a photostationary state very quickly (mostly within 10 minutes) compared to the controls which all showed reduced colouration speeds. It is noteworthy that all naphthopyran samples also exhibited a bathochromic shift (10-15 nm) in the wavelength of their open forms within the lens matrix with respect to that in toluene. This can be accounted for by the partly polar nature of the lens matrix incorporating substantial PEG units and its interaction with their more polar transition states. Such effects are likely to have little consequence on the

151 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______overall speed, with all samples displaying significantly slowed kinetics compared to those in toluene as a result of the rigidity of the matrix.

5.3 Conclusion

In conclusion, I have shown that the attachment of PDMS to various methoxy substituted naphthopyrans gives markedly superior photochromic performance in colouration and decolouration speeds and, for a majority of the samples tested, greater colourabilties within a rigid host matrix. This is made possible by providing a favourable localized environment for attached dyes and their aggregates, all acting to overcome the restrictions imposed on mobility by the rigid matrix. Efficient routes that were used to access the relevant starting materials necessary to generate the hydroxyl functionalized naphthopyrans and subsequent conjugates were also presented as part of the investigation.

5.4 Experimental Details

Materials. All chemicals (reagents and solvents) were of high purity and used as received unless otherwise stated. Reagents for synthesis were obtained from Aldrich at the highest purity available and used without further purification. Carbinol (hydroxyl-terminated) poly(dimethylsiloxane) was purchased from Gelest Inc. All chromatography was performed using silica gel (Kieselgel Merck 60, 0.040 - 0.063 mm) and TLC was performed on Merck Silica 60F254 plates. Methyl 1,4-dihydroxy-2-naphthoate (2a) and methyl 4-hydroxy-6-methoxy-2- naphthoate (6a) were prepared using literature procedures.18,22 The synthesis of 4- hydroxy-1-phenyl-2-naphthoic acid (7) was performed using a patent procedure.21 5-Hydroxy-7H-benzo[C]fluoren-7-one (9) was synthesized using the procedure of Aki et al.28 5-Hydroxy-7H-benzo[C]fluoren-7-ol (10) was synthesized using the procedure of Zeynizadeh et al.29 4-Hydroxy-4’-methoxybenzophenone (11) was synthesized using a procedure adapted from literature.31 4-(3-Hydroxypropoxy)- phenyl-4'-methoxybenzophenone (12) was synthesized as reported in patent literature.32 Propynols 13, 14 and 15 were prepared using lithium trimethylsilylacetylide, as in literature.15 Francesca Ercole acknowledges the contribution of Dr Nino Malic in this work for the synthesis of indeno-fused naphthopyran control 22a and PDMS conjugate 22b.

152 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

General Experimental Measurements. 1H (400 MHz/200 MHz) and 13C (100 MHz/ 50MHz) NMR spectra were obtained with a Bruker AV400 or a Bruker AC200 spectrometer at 25 °C. Spectra were recorded for samples dissolved in dueterated solvent and chemical shifts are reported as parts per million from external tetramethylsilane and J values are given in Hz. Positive ion EI mass spectra were run on a ThermoQuest MAT95XL mass spectrometer using ionization energy of 70 eV. Accurate mass measurements were obtained with a high resolution of 5000 - 10000 using PerFlouroKerosene (PFK) as the reference sample. Positive and negative ion electrospray mass spectra (ESI-MS) were acquired with a VG Platform mass spectrometer using a cone voltage of 50V with the source maintained at 80 °C. Methanol was used as solvent system with a flow rate of 0.04 mL/min.

Molecular weights of PDMS were obtained from 1H NMR spectra from integration values of CH2 resonances along backbone with respect to those of Si(CH3)2. Final molecular weights of PDMS-naphthopyran conjugates were additionally confirmed from integration of charcteristic naphthopyran end-groups. Example 1H NMR spectra are displayed in Appendix 3.

Preparation of Photochromic Lens Samples. Photochromic analyses were performed on cured lenses: PDMS-naphthopyran conjugates and their corresponding controls were individually dissolved in a standard industrial lens formulation comprising 1:4 weight ratio poly(ethylene glycol)(400) dimethacrylate (PEGDMA) and 2,2’-bis((4-methacryloxyethoxy)phenyl)propane (EBPDMA) with 0.4% azobis(isobutyronitrile) (AIBN) (Figure 1). The formulation was the cured at 80 °C for 16 hrs in a standard mould to give optically clear test samples of equivalent thickness (~ 2.4 mm). The doping concentrations were chosen in order to maintain optical densities recorded for kinetic tests in a meaningful range for the detector (refer to those entries in Table 2).

Photochromic Analysis. Under continuous irradiation, the photochromic responses of the lenses were analyzed on a light table (schematic representation available in literature)39 comprised of a Cary 50 spectrophotometer to measure absorbance values and a 160 W Oriel xenon lamp as an incident light source. A series of two filters (Edmund Optics WG320 and Edmund Optics band-pass filter U-340) were used to restrict the output of the lamp to a narrow band (350-400 nm). The samples

153 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______were maintained at 20 °C and monitored at the maximum absorbance of the coloured form for a period of 1000 seconds. Then the thermal decolouration was monitored in the dark for a further 4800 seconds (maximum). Control samples were also analysed in solution using toluene as the solvent in a quartz cell with 1 cm path length. Concentrations ranged from 10-4 to 10-5 M, refer to entries in Table 2.

Starting Materials Synthesis of methyl 1,4-dihydroxy-2-naphthoate (2a). This compound was prepared from 1,4-dihydroxy-2-naphthoic acid (1) using literature procedures.18,22 1H NMR (400

MHz, d6-acetone) : 3.98 (s, 3H, COOCH3), 7.19 (s, 1H, ArH), 7.64 (m, 2H, ArH), 8.21 (d, J 8.4 Hz, 1H, ArH), 8.33 (d, J 8.4 Hz, 1H, ArH), 8.66 (br s, 1H, ArOH), 11.54 (s, 13 1H, ArOH) ppm. C NMR (100 MHz, d6-acetone) : 52.9, 105.1, 105.69, 123.2, 124.4, 126.4, 127.2, 129.7, 130.5, 146.0, 155.2, 172.2 ppm. Mass Spec (EI): m/z 218.0 ([M]+

45%), 186 (100), 130.0 (45), 102.0 (52). Mass Spec (HR, EI): m/z 218.0575 (C12H10O4 requires 218.0579).

Synthesis of methyl 4-hydroxy-1-methoxy-2-naphthoate (2b). 1,4-Dihydroxy-2- naphthoic acid (1) (2.00 g, 9.80 mmol) and K2CO3 (5.40 g, 39.18 mmol) were dissolved in a mixture of water (50 mL) and i-PrOH (10 mL). The solution was cooled to -15 C in an EtOH / dry ice bath and propionyl chloride (1.30 mL, 1.36 g, 14.7 mmol) was added dropwise with vigorous stirring over a period of 5 minutes. The mixture was left to stir at -15 C for an additional 15 minutes and then quenched by the dropwise addition of aqueous 6 M HCl to pH ~ 5 (Caution - foaming). The solid was then collected by filtration, washed with water and dried under vacuum overnight at 40 C to give 1-hydroxy-4-(propionyloxy)-2-naphthoic acid (2.20 g, 75% pure by 1H nmr). The solid was dissolved in dry acetone (180 mL) and then treated with finely ground anhydrous K2CO3 (7.20 g, 52.1 mmol). The mixture was heated to reflux for 30 minutes and then cooled to 0 C with an ice bath. Iodomethane (4.5 mL, 10.3 g, 72.3 mmol) was then added dropwise over 5 minutes via syringe and the resulting mixture was left to stir at room temperature for 16 hours. Removal of the solvent and excess reagents under vacuum gave a brown paste that was re-dissolved into diethyl ether and filtered through a plug of silica gel to remove baseline material. The solvent was then removed under vacuum and the brown gum was collected to afford methyl 1-hydroxy-

4-(propionyloxy)-2-naphthoate as a crude product. Finely ground K2CO3 (1.64 g, 11.9 mmol) was added to a suspension of the crude material (2.74 g) in methanol (15 mL) 154 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______and the resulting suspension was stirred at room temperature for 3 hours. The mixture was then diluted with water (100 mL), acidified by the addition of aqueous 2M HCl and extracted into diethyl ether (3 × 75 mL). The combined organic extracts were washed with 10% NaHCO3 (3 × 75 ml) and water (1 × 100 ml). The product was then extracted from the organic layer into an aqueous basic layer using 0.1M NaOH (5 × 50 mL). The combined basic aqueous layers were then acidified with aqueous 2M HCl to pH~5 and extracted with diethyl ether (3 × 75 mL). The combined organic layers were then washed with saturated brine and dried with anhydrous MgSO4. Solvent removal yielded the pure final product, methyl 4-hydroxy-1-methoxy-2-naphthoate (2b), as a tan solid 1 (1.70 g, 75%). H NMR (400 MHz, d6-acetone) : 3.90 (s, 3H, ArOCH3), 3.96 (s, 3H,

COOCH3), 7.22 (s, 1H, ArH), 7.59 - 7.64 (m, 2H, ArH), 8.17 - 8.21 (m, 1H, ArH), 8.22 13 - 8.27 (m, 1H, ArH), 9.07 (s, 1H, ArOH) ppm. C NMR (100 MHz, d6-acetone) : 52.4, 63.5, 108.3, 120.6, 123.5, 124.2, 127.9, 128.2, 129.0, 130.3, 149.9, 151.5, 167.1 ppm. Mass Spec (EI): m/z 232.1 ([M]+ 100%), 217.1 (68), 201.1 (22), 170.0 (20), 161.1 (27), 142.1 (17), 131.0 (18), 115.1 (24), 102 (24), 83.9 (89), 69.1 (54). Mass Spec (HR, EI): m/z 232.0729 (C13H12O4 requires 232.0736).

Synthesis of 4-hydroxy-6-methoxy-2-naphthoic acid (5). The Stobbe condensation of 4-methoxybenzaldehyde with diethyl succinate affected either by t-BuOK (2.2 equivalents, toluene, room temperature, 16 hours)23 or sodium ethylate (Na in dry ethanol (NaOEt), 2 equivalents, reflux 3 hours)24 resulted in considerable proportion (~ 35%) of by-product, 2,3-bis(4-methoxybenzylidene)succinic acid (3b), isolated as a pale yellow crystalline material as well as the desired half ester product, 3a.18 The 1H NMR 1 showed a mixture of geometrical isomers for 3b: H NMR (400 MHz, CD6SO) : 3.73 and 3.79 (2 × s, 6H, ArOCH3), 6.89 (d, J 8.8 Hz, 2H, ArH), 7.01 (d, J 8.8 Hz, 2H, ArH), 7.38 (d, J 8.4 Hz, 2H, ArH), 7.50 (d, J 8.4 Hz, 2H, ArH), 7.68 and 7.72 (2 × s, 2H, olefinic H) ppm. A second alternative literature procedure26 was also used to prepare the half ester 3a which resulted in no by-product: To a mixture of 4- methoxybenzaldehyde (2.00 g, 14.7 mmol), diethyl succinate (2.56 g, 14.7 mmol) was added powdered t-BuOK (2.17 g, 17.7 mmol). The mixture was ground with a mortar and pestle for 10 minutes and then left to sit at room temperature for 3 hours. The thick paste was then dissolved in water and the resulting basic solution was washed with diethyl ether (3 × 100 mL). The basic solution was then neutralized with 2 M HCl and re-extracted back into diethyl ether (3 × 100 mL). The organic layers were combined

155 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______and washed with saturated brine, dried with anhydrous MgSO4 and the solvent removed under reduced pressure to give a thick amber oil (3a, 2.9 g, 75%) in sufficient purity for subsequent steps. Friedel Crafts acylation of the crude half ester mixture (3a), using procedures outlined in literature,18, 23-25 followed by saponification yielded 4-hydroxy- 6-methoxy-2-naphthoic acid, (5) as a pale pink powder (35% overall yield for the three 1 steps). H NMR (400 MHz, d6-acetone) : 3.95 (s, 3H, ArOCH3), 7.22 (dd, 1H, J 8.7 Hz, 1.5 Hz, ArH), 7.49 (br d, 1H, J 1.5 Hz, ArH), 7.58 (d, J 1.5 Hz, 1H, ArH), 7.92 (d, J 8.7 Hz, 1H, ArH), 8.12 (s, 1H, ArH), 9.21 (s, 1H, ArOH) ppm. 13C NMR (100 MHz, d6-acetone) : 55.1, 100.7, 108.0, 119.8, 122.6, 126.1, 128.8, 129.5, 131.0, 152.4, 159.4, 167.3 ppm. ESI-MS m/z 217.3 [M-H]-

Synthesis of methyl 4-hydroxy-6-methoxy-2-naphthoate (6a). This compound was synthesized from 4-hydroxy-6-methoxy-2-naphthoic acid (5) using a literature 18 1 procedure. H NMR (400 MHz, d6-acetone) : 3.88 (s, 3H, COOCH3), 3.95 (s, 3H,

ArOCH3), 7.22 (dd, J 8.7 Hz, 1.5 Hz, 1H, ArH), 7.46 (br d, J 1.5 Hz, 1H, ArH), 7.57 (d, J 1.5 Hz, 1H, ArH), 7.91 (d, J 8.7 Hz, 1H, ArH), 8.07 (s, 1H, ArH), 9.21 (s, 1H, ArOH) 13 ppm. C NMR (100 MHz, d6-acetone) : 52.7, 56.2, 101.8, 108.7, 121.1, 123.4, 126.9, 129.9, 130.5, 132.1, 153.6, 160.6, 168.0 ppm. Mass Spec (EI): m/z 232.1 ([M]+ 100%), 201.1 (48), 189.1 (17), 173.1 (26), 102 (14). Mass Spec (HR, EI): m/z 232.0727

(C13H12O4 requires 232.0736).

Synthesis of 3-hydroxypropyl-4-hydroxy-6-methoxy-2-naphthoate (6b). This compound was synthesized using an alkylation procedure adapted from that of Hattori et al.22 4-Hydroxy-6-methoxy-2-naphthoic acid (5) (4.82 g, 22.1 mmol) and anhydrous sodium bicarbonate (1.86 g, 22.1 mmol) were added to DMF (20 mL) and stirred at 100 °C for 30 minutes under argon. The solution was cooled with an ice bath and then sodium iodide (6.63 g, 44.2 mmol) was added, followed by the dropwise addition of 3- chloropropanol (4.20 g, 44.2 mmol, 3.80 mL). The mixture was stirred for an additional 3 hours at 100 °C and was then poured into dilute aqueous HCl and extracted into diethyl ether (3 × 75 ml). The combined organic extracts were washed with 10%

NaHCO3 (3 × 75 ml) and water (1 × 100 ml). The product was then extracted from the organic layer with 0.1 M NaOH (5 × 50 ml). The combined basic aqueous layers were then acidified with aqueous 2M HCl, extracted with diethyl ether (3 × 75 ml), washed with saturated brine and dried (anhydrous MgSO4). Solvent removal under vacuum yielded the pure final product, 3-hydroxypropyl-4-hydroxy-6-methoxy-2-naphthoate

156 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

1 (6b), as an off-white solid (3.95 g, 65%). H NMR (400 MHz, d6-acetone) : 1.98 (p,

2H, J 6.2 Hz, CH2CH2CH2), 3.68 (br s, OH), 3.75 (t, J 6.2 Hz, 2H, CH2OH), 3.95 (s,

3H, ArOCH3), 4.42 (t, 2H, J 6.2 Hz, CH2CH2CH2) 7.22 (dd, J 8.7, 2.5 Hz, 1H, ArH), 7.47 (br d, J 1.5 Hz, 1H, ArH), 7.57 (d, J 1.5 Hz, 1H, ArH), 7.92 (d, J 8.7 Hz, 1H, ArH), 13 8.09 (s, 1H, ArH), 9.19 (br s, 1H, ArOH) ppm. C NMR (100 MHz, d6-acetone) : 32.0, 54.8, 58.1, 61.7, 100.4, 107.4, 119.6, 122.0, 125.8, 128.5, 129.2, 130.7, 152.2, 159.1, 166.2 ppm. Mass Spec (EI): m/z 276.1 ([M]+ 100%), 218.0 (69), 201.0 (58), 175.0 (41), 145.1 (13), 130.0 (12), 115.1 (10), 102 (22). Mass Spec (HR, EI): m/z

276.0988 (C15H16O5 requires 276.0988).

Synthesis of 4-hydroxy-1-phenyl-2-naphthoic acid (7). The synthesis of this compound from benzophenone was performed using a patent literature procedure.21 1 H NMR (200 MHz, d6-acetone) : 7.25 - 7.30 (m, 2H, Ar-H), 7.40 - 7.46 (m, 6H, ArH), 13 7.51 - 7.59 (m, 1H, ArH), 8.34 (d, J 8.2 Hz, 1H, ArH) ppm. C NMR (50 MHz, d6- acetone) : 109.3, 121.9, 123.9, 128.0, 128.7, 128.7, 129.0, 129.6, 131.3, 132.2, 134.0, 135.8, 141.3, 154.3, 170.5 ppm. ESI-MS m/z 263.4 [M-H]-.

Synthesis of 2-hydroxyethyl-4-hydroxy-1-phenyl-2-naphthoate (8). The synthesis of this compound was also performed using the alkylation procedure of Hattori et al.22

1-Phenyl-2-carboxy-4-naphthol (2.00 g, 7.57 mmol) and NaHCO3 (0.636 g, 7.57 mmol) were added to DMF (20 mL) and stirred at 60 °C for 2 hours under nitrogen, then at 100 °C for 15 minutes. Freshly distilled and acid-free 2-bromoethanol (1.14 g, 9.08 mmol, 0.64 mL) was then added and the mixture stirred for an additional 1.25 hours at 100 °C. The mixture was poured into dilute aqueous HCl and extracted with diethyl ether. The ether layer was washed several times with water, then with saturated brine and dried with anhydrous MgSO4. The solvent was removed under vacuum to give the pure 1 product as an off-white solid (2.16 g, 93%). H NMR (200 MHz, d6-acetone) : 3.43 (t,

J 5.2 Hz, 2H, CH2OH), 4.00 (t, J 5.2 Hz, 2H, OCOCH2CH2), 7.26 - 7.31 (m, 2H, ArH), 7.35 (s, 1H, ArH), 7.40 - 7.62 (m, 6H, ArH), 8.35 (dd, J 8.3 Hz, 1.1 Hz, 1H, ArH) ppm. 13 C NMR (50 MHz, d6-acetone) : 60.3, 67.0, 108.1, 123.0, 127.1, 127.2, 127.8, 127.9, 128.0, 128.7, 129.9, 131.1, 133.1, 134.6, 140.4, 153.3, 168.7 ppm. ESI-MS m/z 307.4 [M-H]-.

Synthesis of 5-hydroxy-7H-benzo[C]fluoren-7-one (9). This compound was synthesized using the procedure of Aki et al.28 4-Hydroxy-1-phenyl-2-naphthoic acid,

157 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

(7), (2.00 g, 7.57 mmol) was added in portions, with stirring, to methanesulfonic acid (15 mL) at 60 °C. The mixture was stirred for an additional 1.5 hours and then slowly poured into ice water. The purple solid was collected by filtration, thoroughly washed with water and dried in a vacuum oven at 50 °C overnight, giving the product with 1 excellent purity (1.70 g, 91%). H NMR (200 MHz, d6-acetone) : 7.15 (s, 1H, ArH), 7.28 (t, J 7.4 Hz, 1H, ArH), 7.52 -7.77 (m, 4H, ArH), 8.11 (d, J 8.1 Hz, 1H, ArH), 8.37 13 (m, 1H, ArH), 8.59 (m, 1H, ArH), 9.74 (br s, 1H, ArOH) ppm. C NMR (50 MHz, d6- DMSO) : 101.5, 122.3, 123.3, 123.6, 124.6, 127.1, 127.3, 128.1, 128.5, 129.2, 132.1, 132.4, 133.5, 135.1, 145.0, 155.2, 193.9 ppm. ESI-MS m/z 245.4 [M-H]-

Synthesis of 5-hydroxy-7H-benzo[C]fluoren-7-ol (10). This compound was synthesized using the procedure of Zeynizadeh et al.29 5-Hydroxy-7H-benzo[C]fluoren- 7-one (9), (1.60 g, 6.50 mmol) was added to THF (36 mL) followed by water (1.2 mL). The mixture was heated at 50 °C and then sodium borohydride (0.492 g, 12.99 mmol) was added in one portion. The mixture was stirred for 20 minutes, poured into dilute aqueous HCl and extracted with ethyl acetate. The organic layer was washed with water, saturated brine, dried with anhydrous MgSO4 and filtered through a short column of silica gel. The solvent was removed under vacuum to give the product as an off-white 1 solid with excellent purity (1.57 g, 97%). H NMR (200 MHz, d6-acetone) : 4.68 (s,

1H, Ar2CH), 7.24 (t, J 7.4, 0.98 Hz, 1H, ArH), 7.30 (s, 1H, ArH), 7.42 (m, 1H, ArH), 7.52 (m, 1H, ArH), 7.61 - 7.71 (m, 2H, ArH), 8.19 (d, J 7.7 Hz, 1H, ArH), 8.38 (d, J 8.4 13 Hz, 1H, ArH), 8.67 (d, J 8.4 Hz, 1H, ArH) ppm. C NMR (50MHz, d6-DMSO) : 74.4, 105.9, 121.6, 123.8, 124.1, 124.7, 124.9, 125.0, 125.4, 125.4, 127.8, 128.9, 130.0, 141.3, 147.7, 148.0, 154.3 ppm. ESI-MS m/z 247.4 [M-H]-.

Synthesis of 4-hydroxy-4’-methoxybenzophenone (11). This compound was synthesized from anisole and 4-hydroxy benzoic acid using a procedure adapted from literature.31 The reaction mixture was poured into ice/water and the residue was washed with plenty of cold water until the acidity of the water was pH 4-5. The crude precipitate was then recrystallized from methanol by gradual addition of water (approx. 30% v/v of methanol in water). It was then dried in a vacuum oven overnight at 40 C 1 and isolated as a tan crystalline solid (8.9 g, 60%). H NMR (400 MHz, d6-acetone) :

3.89 (s, 3H, ArOCH3), 6.96 (d, J 8.8 Hz, 2H, ArH,), 7.04 (d, J 8.8 Hz, 2H, ArH), 7.75 (d, J 8.4 Hz, 2H, ArH), 7.69 (d, J 8.4 Hz, 2H, ArH), 9.12 (s, 1H, ArOH) ppm. 13C

158 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

NMR (100 MHz, d6-acetone) : 55.0, 113.4, 114.9, 129.8, 130.9, 131.8, 132.1, 161.1, 162.8, 193.1 ppm. ESI-MS m/z 227.4 [M-H]-.

Synthesis of 4-(3-hydroxypropoxy)-phenyl-4'-methoxybenzophenone (12). This compound was synthesized from 4-hydroxy-4’-methoxybenzophenone (11) using Williamson etherification conditions, as reported in patent literature.32 The product was isolated as a white powder after recrystallization from EtOAc (1.60 g, 50%). 1H NMR

(400 MHz, CDCl3) : 1.63 (t, J 5.1 Hz, 1H, CH2OH), 2.06 - 2.12 (m, 2H, CH2CH2CH2),

3.87 - 3.91 (m, 5H, ArOCH3 and CH2OH), 4.21 (t, J 5.9 Hz, 2H, CH2CH2CH 2), 6.95 - 13 6.74 (m, 4H, ArH), 7.77 - 7.79 (m, 4H, ArH) ppm. C NMR (100 MHz, CDCl3) : 31.9, 55.5, 60.1, 65.6, 113.5, 114.0, 130.8, 130.9, 132.3, 132.3, 162.1, 162.9, 194.5 ppm. Mass Spec (EI): m/z 286.1 ([M]+ 77%), 228.1 (28), 197.0 (15), 179.1 (19), 135.0

(100), 121.0 (50). Mass Spec (HR, EI): m/z 286.1195 (C17H18O4 requires 286.1205).

Synthesis 1-(4-(3-hydroxypropoxy)phenyl)-1-(4-methoxyphenyl)prop-2-yn-1-ol (13). This compound was synthesized from 4-3-hydroxypropoxy)-phenyl-4'- methoxybenzophenone (12) following the same procedure as detailed in literature,15 however using 2 molar equivalents of (trimethylsilyl)acetylene and n-butyl lithium (1.6M in hexane) compared (12). It was isolated quantitatively as a pale yellow oil in 1 sufficient purity for subsequent use. H NMR (400 MHz, d6-benzene) : 1.62 (p, J 6.1

Hz, 2H, CH2CH2CH2), 2.38 (s, 1H, CCH), 3.25 (s, 3H, ArOCH3), 3.43 (t, J 6.1 Hz,

2H,CH2OH), 3.65 (t, J 6.1 Hz, 2H, CH2CH2CH2), 6.23 - 6.76 (m, 4H, ArH), 7.62 - 7.75 13 (m, 4H, ArH) ppm. C NMR (400 MHz, d6-benzene) : 32.7, 51.2, 60.1, 65.6, 74.2, 75.3, 87.9, 114.2, 114.7, 138.4, 138.5, 159.3, 156.0 ppm. Mass Spec (EI): m/z 312.1 ([M]+ 100%), 295.1 (47), 253.1 (79), 237.1 (43), 205.1 (20), 165.1 (25), 161.1 (39),

147.1 (20), 135.0 (36)108 (19). Mass Spec (HR, EI): m/z 312.1356 (C19H20O4 requires 312.1362).

Synthesis 1,1-bis(4-methoxyphenyl)prop-2-yn-1-ol (14). This compound was synthesized from 4,4’-dimethoxybenzophenone using the standard literature procedure.15 It was isolated quantitatively as a tan coloured solid in sufficient purity for 1 subsequent use. H NMR (400 MHz, d6-acetone) : 3.28 (s, 1H, CCH), 3.76 (s, 6H,

ArOCH3), 5.42 (s, 1H, OH), 6.85 (d, J 8.8 Hz, 4H, ArH), 7.49 (d, J 8.8 Hz, 4H, ArH) 13 ppm. C NMR (100 MHz, d6-acetone) : 54.9, 73.0, 75.1, 87.9, 113.3, 127.4, 138.7, 159.0 ppm. Mass Spec (EI): m/z 268.1 ([M]+ 100%), 267.1 (27), 251.1 (48), 242.1 (16),

159 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

237.1 (28), 161.1 (48), 135.1 (59), 108 (17). Mass Spec (HR, EI): m/z 268.1094

(C17H16O3 requires 268.1099).

Synthesis 1-(4-methoxy-phenyl)-1-phenylprop-2-yn-1-ol (15). This compound was synthesized from 4-methoxybenzophenone using the same standard literature procedure15 as (14) and isolated quantitatively as a colourless oil, in sufficient purity for 1 subsequent use. H NMR (400 MHz, d6-acetone) : 2.87 (s, 1H, CCH), 3.78 (s, 3H,

ArOCH3), 6.86 (d, J 8.8 Hz, 2H, ArH), 7.26 - 7.36 (m, 3H, ArH), 7.52 (d, J 8.8 Hz, 2H, 13 ArH), 7.61 (d, J 7.3 Hz, 2H, ArH) ppm. C NMR (400 MHz, d6-acetone) : 54.7, 73.1, 75.2, 87.4, 113.2, 125.9, 127.1, 127.3, 127.9, 138.2, 146.3, 159.0 ppm. Mass Spec (EI): m/z 238.1 ([M]+ 79%), 221.1 (25), 207.1 (13), 178.1 (18), 161.1 (100), 135.0 (14), 108.0

(25). Mass Spec (HR, EI): m/z 238.0986 (C15H16O5 requires 238.0994).

Hydroxyl functionalized naphthopyrans Synthesis of methyl 6-hydroxy-2,2-bis(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran -5-carboxylate (16). The synthesis of the title photochromic compound4 from methyl 1,4-dihydroxy-2-naphthoate (2a) and 1,1-bis(4-methoxyphenyl)prop-2-yn-1-ol (14) has been described by us elsewhere39 using a procedure adapted from a literature.26 The product was isolated by crystallization from diethyl ether as a bright yellow solid (0.97 1 g, 45%). H NMR (400 MHz, d6-acetone) : 3.73 (s, 6H, 2 × ArOCH3), 4.05 (s, 3H,

COOCH3), 6.32 (d, J 10.0 Hz, 1H, pyran-H), 6.86 (d, J 8.8 Hz, 4H, ArH), 7.45 (d, J 8.8 Hz, 4H, ArH), 7.48 (d, J 10.0 Hz, 1H, pyran-H), 7.59 (m, J 8.4 and 1.5 Hz, 1H, ArH), 7.75 (m, J 8.4 and 1.5 Hz, 1H, ArH), 8.31 (d, J 8.4 Hz, 1H, ArH), 8.39 (d, J 8.4 Hz, 1H, 13 ArH), 12.18 (s, 1H, ArOH) ppm. C NMR (100 MHz, d6-acetone) : 53.8, 56.2, 82.6, 104.0, 115.0, 115.2, 123.5, 125.0, 125.6, 126.7, 128.4, 129.5, 129.9, 130.3, 131.5, 138.7, 142.7, 157.8, 160.7, 173.7 ppm. Mass Spec (EI): m/z 468.2 ([M]+ 92%), 436.2 (100), 408.2 (38), 391.2 (18), 377.1 (13), 330.1 (39), 218.1 (16). Mass Spec (HR, EI): m/z 468.1564 (C29H24O6 requires 468.1573).

Synthesis of methyl 6-hydroxy-2-(4-methoxy-phenyl)-2-phenyl-2H-naphtho[1,2- b]pyran-5-carboxylate (17). The title compound4 was synthesized from methyl 1,4- dihydroxy-2-naphthoate (2a) and 1-(4-methoxy-phenyl)-1-phenylprop-2-yn-1-ol (15) using the same general procedure as that used to synthesize (16). The product was isolated by crystallization from diethyl ether/hexane as a yellow solid (4.30 g, 71%). 1H

NMR (400 MHz, d6-acetone) : 3.72 (s, 3H, ArOCH3), 4.04 (s, 3H, COOCH3), 6.37 (d,

160 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

J 9.9 Hz, 1H, pyran-H), 6.84 (apparent d, J 8.8 Hz, 2H, ArH), 7.22 - 7.25 (m, 1H, ArH), 7.31 - 7.34 (m, 2H, ArH), 7.47 (apparent d, J 8.8 Hz, 2H, ArH), 7.51 (d, J 9.9 Hz, 1H, pyran-H), 7.56 - 7.61 (m, 3H, ArH), 7.73 - 7.77 (m, 1H, ArH) 8.32 (d, J 8.4 Hz, 1H, 13 ArH), 8.4 (d, J 8.4 Hz, 1H, ArH), 12.19 (s, 1H, ArOH) ppm. C NMR (100 MHz, d6- acetone) : 53.1, 55.5, 82.0, 103.3, 114.3, 114.6, 122.8, 124.5, 124.8, 126.0, 127.3, 127.7, 128.2, 128.8, 128.9, 129.0, 129.5, 130.9, 137.6, 141.9, 146.2, 157.2, 160.1, 173.0 ppm. Mass Spec (EI): m/z 438.1 ([M]+ 28%), 406.1 (100), 375.1 (16), 361.1 (13), 298.0

(12), 289.1 (14), 276.1 (12), 203.1 (13). Mass Spec (HR, EI): m/z 438.1456 (C28H22O5 requires 438.1462).

Synthesis of methyl 6-methoxy-2-(4-(3-hydroxypropoxy)phenyl)-2-(4- methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (18). The title compound was synthesized from methyl 4-hydroxy-1-methoxy-2-naphthoate (2b) and 1-(4-(3- hydroxypropoxy)phenyl)-1-(4-methoxyphenyl)prop-2-yn-1-ol (13) using the alternative procedure described in literature.15, 30 The product was isolated as a deep red solid (230 mg, 40%) after purification by column chromatography (silica gel, 1 MeOH/EtOAc/Toluene, 0.5:2:7.5). H NMR (400 MHz, d6-benzene) : 1.59 (quintet, J

6.1 Hz, 2H, CH2CH2CH2), 3.21 (s, 3H, ArOCH3), 3.37 - 3.41 (m, 2H, CH2OH), 3.55 (s,

3H ArOCH3), 3.61 (t, J 6.1 Hz, 2H, CH2CH2CH2), 3.67 (s, 3H, COOCH3), 6.04 (d, J 9.9 Hz, 1H, pyran-H), 6.68 - 6.72 (m, 4H, ArH), 6.92 (d, J 9.9 Hz, 1H, pyran-H), 7.15 - 7.20 (m, 1H, ArH), 7.24 - 7.28 (m, 1H, ArH), 7.48 - 7.52 (m, 4H, ArH), 7.95 (d, J 8.4 13 Hz, 1H, ArH), 8.46 (d, J 8.4 Hz, 1H, ArH) ppm. C NMR (100 MHz, d6-benzene) : 32.7, 52.2, 55.1, 60.0, 63.5, 65.8, 83.6, 114.1, 114.3, 114.8, 121.7, 121.7, 123.2, 123.6, 127.4, 127.6 127.7, 129.1, 129.2, 129.2, 129.9, 137.8, 137.8, 145.3, 149.2, 159.3, 160.0, 167.9 ppm. Mass Spec (EI): m/z 526.2 ([M]+ 100%), 494.2 (43), 479.1 (85), 451.1 (11), 435.1 (35), 421.1 (50), 393.1 (15), 375 (20), 276.1 (11), 218.1 (20). Mass Spec (HR,

EI): m/z 526.1970 (C32H30O7 requires 526.1992).

Synthesis of 3-hydroxypropyl 9-methoxy-2,2-bis(4-methoxyphenyl)-2H- naphtho[1,2-b]pyran-5-carboxylate (19). The title compound was synthesized using a procedure adapted from literature.17 3-Hydroxypropyl-4-hydroxy-6-methoxy-2- naphthoate (6b) (0.578 g, 2.09 mmol), pyridinium p-toluenesulfonate (26.26 mg, 0.11 mmol) and trimethylorthoformate (0.303 g, 2.90 mmol, 0.31 mL) were added to 1,2- dichloroethane (10 mL) and heated to 70 °C with stirring. After dissolution of the naphthol a solution of 1,1-bis(4-methoxyphenyl)prop-2-yn-1-ol (14) (0.510 g, 1.9

161 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______mmol) in 1,2-dichloroethane (8 mL) was added slowly over 10 minutes. The mixture was heated to reflux for a further 2.5 hours under nitrogen. TLC analysis showed the presence of a number of photochromic species. The solvent was removed under vacuum and the residue purified by column chromatography (silica gel, ethyl acetate/hexane, 1:1). The main photochromic fraction was collected (lower Rf), giving the desired product as a pale pink solid (0.10 g) after removal of the solvent under vacuum. The solvent was removed from the other combined fractions (higher Rf) giving a residue containing a photochromic by-product. It was dissolved in a small amount of acetone, a few drops of 2M HCl were added and then it was heated gently in a water bath at 60 °C for 2 hours. When TLC analysis showed complete conversion of the photochromic by-product to the desired photochromic product the solvent was removed under vacuum, leaving behind a residue which was subsequently purified by column chromatography as above to give 3-hydroxypropyl 9-methoxy-2,2-bis(4- methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (19). The combined mass from the two crops was: 0.55 g, 55%. Note: The photochromic by-products most likely arise from the trans-acetalization of trimethylorthoformate with the hydroxy functionality of the naphthol starting material and the hydroxylated photochromic product, giving a (mixed) acetal by-product. The free hydroxy group is regenerated by hydrolysis under 1 acidic conditions. H NMR (400 MHz, d6-acetone) : 1.99 (quintet, 6.3 Hz, 2H,

CH2CH2CH2), 3.70 (t, J 5.2 Hz, 1H, OH), 3.73 - 3.78 (overlapping m, 2H, CH2OH and s, 6H, 2 × ArOCH3), 3.98 (s, 3H, COOCH3), 4.44 (t, J 6.3 Hz, 2H, CH2CH2CH2), 6.39 (d, J 10.0 Hz, 1H, pyran-H), 6.84 - 6.92 (m, 4H, ArH), 7.21 (dd, J 8.9 Hz, J 2.6 Hz, 1H, ArH), 7.43 - 7.51 (m, 4H, ArH), 7.68 - 7.70 (overlapping d, J 10.0 Hz, 1H, pyran-H and br d, J 2.6 Hz, 1H, ArH), 7.86 (d, J 8.9 Hz, 1H, ArH), 8.06 (s, 1H, ArH) ppm. 13C NMR

(100 MHz, d6-acetone) : 33.6, 56.3, 56.7, 59.9, 63.6, 83.6, 101.9, 115.0, 117.5, 121.4, 123.6, 124.0, 126.1, 129.6, 129.7, 129.8, 130.7, 132.4, 138.7, 149.1, 160.8, 161.5, 168.2 ppm. Mass Spec (EI): m/z 526.3 ([M]+ 52%), 467.2 (49), 450.2 (100), 419.2 (47), 342.1

(11), 225.1 (25). Mass Spec (HR, EI): m/z 526.1966 (C32H30O7 requires 526.1992).

Synthesis of 3-hydroxypropyl 9-methoxy-2-(4-methoxyphenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (20). The title compound was synthesized from 3- hydroxypropyl-4-hydroxy-6-methoxy-2-naphthoate (6b) and 1-(4-methoxy-phenyl)-1- phenylprop-2-yn-1-ol (15) using the same procedure as (16) and (17). The product was purified by column chromatography (silica gel, chloroform / ethyl acetate / hexane,

162 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

5:4:1) and isolated as an orange crunchy solid after removal of solvent under vacuum 1 (0.76 g, 30%). H NMR (400 MHz, d6-acetone) : 1.98 (quintet, 2H, J 6.2 Hz,

CH2CH2CH2), 3.68 (s br, OH), 3.72 - 3.76 (m, 2H, CH2OH and s, 3H, ArOCH3), 3.99

(s, 3H, 9-ArOCH3), 4.42 (t, J 6.2 Hz, 2H, CH2CH2CH2), 6.43 (d, J 10.0 Hz, 1H, pyran- H), 6.86 (d, J 8.8 Hz, 2H, ArH), 7.20 - 7.36 (m, 4H, ArH), 7.48 (d, J 8.8 Hz, 2H, ArH), 7.57- 7.59 (m, 2H, ArH), 7.69 - 7.72 (m, 1H, ArH overlap with d, J 10.0 Hz, 1H, pyran- 13 H), 7.86 (d, J 8.8 Hz, 1H, ArH), 8.09 (s, 1H, ArH) ppm. C NMR (100 MHz, d6- acetone) : 32.8, 55.6, 56.0, 59.1, 62.9, 83.0, 101.2, 114.4, 116.8, 120.8, 123.2, 123.3, 125.5, 127.4, 128.3, 129.0,129.0, 129.1, 129.1, 129.8, 131.8, 137.7, 146.3, 148.4, 160.2, 160.9, 167.4 ppm. Mass Spec (EI): m/z 496.2 ([M]+ 33%), 437.2 (30), 420.1 (100),

392.2 (25), 210.1 (15). Mass Spec (HR, EI): m/z 496.1870 (C31H28O6 requires 496.1886).

Synthesis of 2-hydroxyethyl 2,2-bis(4-methoxyphenyl)-6-phenyl-2H-naphtho[1,2- b]pyran-5-carboxylate (21). The title compound was initially synthesized using a patent procedure,32 the product purified by column chromatography (silica gel, ethyl acetate/hexane, 2:3) and isolated as a red/brown glassy solid after removal of solvent under vacuum (0.58 g, 47%). A second alternative procedure17 was also used as described for the preparation of (19). The product was purified by column chromatography (silica gel, diethyl ether/hexane, 2:1) and isolated as a red/brown glassy 1 solid with a combined mass of product: 0.339 g, 61%. H NMR (400 MHz, d6-acetone)

: 3.44 (m br, 2H, CH2OH), 3.59 (br s, 1H, OH), 3.77 (s, 6H, 2 × ArOCH3), 4.01 (t, J

5.2 Hz, 2H, CH2CH2), 6.44 (d, J 10.0 Hz, 1H, pyran-H), 6.87 (d, J 10.0 Hz, 1H, pyran- H), 6.92 (d, J 8.8 Hz, 4H, ArH), 7.32 (m, 2H, ArH), 7.44 - 7.50 (m, 9H, ArH), 7.61 (m, 13 1H, ArH), 8.46 (d, J 8.5 Hz, 1H, ArH) ppm. C NMR (50MHz, CDCl3) : 55.1, 60.6, 66.7, 82.8, 112.1, 113.5, 120.4, 122.1, 125.2, 126.6, 126.8, 127.0, 127.7, 128.0, 128.1, 128.2, 128.6, 130.4, 130.6, 132.6, 137.1, 138.6, 147.6, 158.9, 168.4 ppm. Mass Spec (EI): m/z 558.2 ([M]+ 73%), 513.2 (35), 496.1 (100), 465.1 (15), 451.1 (23) 248.1 (30) ppm. Mass Spec (HR, EI): m/z 558.2034 (C36H30O6 requires 558.2042).

Synthesis of 3,3-bis(4-methoxyphenyl)-13-hydroxy-indeno[2,1-f]naphtho[1,2- b]pyran (22). The title compound was synthesized according to a patent procedure21 using toluene as solvent in place of dichloromethane. 5-Hydroxy-7H-benzo[C]fluoren- 7-ol (10) (1.00 g, 4.03 mmol) and 1,1-bis(4-methoxyphenyl)prop-2-yn-1-ol (14) (1.19 g, 4.43 mmol) were added to toluene (30 mL) and the mixture heated to reflux for 1

163 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______minute to remove traces of water via azeotrope using a Dean-Starck trap. The mixture was cooled to 60 °C and dodecylbenzenesulfonic acid (ca. 50 mg) added. Stirring was continued at 60 °C for a further 1.5 hours under nitrogen, after which the solvent was evaporated and the residue passed through a short silica gel column, eluting with diethyl ether/hexane (4:1). The solvent was removed under vacuum and the crude product purified by column chromatography (silica gel, ethyl acetate/hexane, 2:5 to 3:5) giving a 1 dark purple-black solid. H NMR (200MHz, d6-acetone) : 3.71 (s, 3H, ArOCH3), 3.72

(s, 3H, ArOCH3), 5.67 (br s, 1H, Ar2CH), 6.42 (d, J 9.9 Hz, 1H, pyran-H), 6.87 (m, 4H, ArH), 7.26 (m, 1H, ArH), 7.45 (m, 6H, ArH), 7.62 (m, 3H, ArH), 8.16 (d, J 7.7 Hz, 1H, 13 ArH), 8.47 (m, 1H, ArH), 8.63 (m, 1H, ArH) ppm. C NMR (50MHz, d6-acetone) : 56.5, 75.8, 84.7, 115.3, 116.1, 122.5, 123.7, 124.8, 125.9, 126.4, 127.2, 127.2, 127.6, 129.1, 129.2, 129.8, 130.4, 130.5, 131.5, 139.3, 139.3, 142.7, 143.4, 149.3, 149.8, 160.9 ppm. ESI-MS m/z 497.2 [M-H]- Mass Spec (EI): m/z 498.2 ([M]+ 88%), 480.1 (100), 463.1 (29), 449.1 (97), 391.1 (22), 372.1 (39), 357.1 (17), 240.2 (63) Mass Spec (HR,

EI): m/z 498.1804 (C34H26O4 requires 498.1831).

Naphthopyran Controls

Synthesis of methyl 2,2-bis(4-methoxyphenyl)-6-(propionyloxy)-2H-naphtho[1,2- b]pyran-5-carboxylate (16a). To a solution of methyl 6-hydroxy-2,2-bis(4- methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (16) (0.20 g, 0.427 mmol) in dry dichloromethane (10 mL) was added triethylamine (0.178 mL, 0.130 g, 1.28 mmol), under nitrogen. Propionyl chloride (0.040 g, 0.427 mmol, 0.037 mL) was added dropwise via a syringe and the mixture stirred at ambient temperature until TLC analysis showed that the reaction was complete (ca. ~15 mins). The solvent and excess reagents were evaporated in vacuo, the residue re-dissolved in diethyl ether (20 mL) and washed successively with 0.1M HCl, water, 0.1M NaHCO3, water and brine. The organic layer was dried with anhydrous MgSO4 and the solvent removed under vacuum. The crude glassy residue was then purified by column chromatography (silica gel, diethyl ether/hexane, 2:1), giving the pure product as a pale pink solid (0.180 g, 79%). 1 H NMR (400MHz, d6-acetone) : 1.26 (t, J 7.5 Hz, 3H, propionyl-CH3), 2.76 (q, J 7.5

Hz, 2H, propionyl-CH2), 3.76 (s, 6H, 2 × ArOCH3), 3.93 (s, 3H, COOCH3), 6.41 (d, J 10.0 Hz, 1H, pyran-H), 6.89 (d, J 8.9 Hz, 4H, ArH), 6.96 (d, J 10.0 Hz, 1H, pyran-H), 7.45 (d, J 8.9 Hz, 4H, ArH), 7.59 (m, 1H, ArH), 7.67 (m, 1H, ArH), 7.85 (d, J 8.4 Hz, 13 1H, ArH), 8.41 (d, J 8.4 Hz, 1H, ArH) ppm. C NMR (50MHz, d6-acetone) : 9.4,

164 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

27.7, 52.8, 55.5, 83.5, 114.3, 114.4, 120.8, 121.6, 123.0, 123.5, 127.1, 128.3, 128.6, 128.8, 128.9, 130.2, 137.7, 140.3, 146.7, 160.1, 166.3, 173.1 ppm. Mass Spec (EI): m/z 524.2 ([M]+ 36%), 568.2 (54), 436.2 (100), 407.1 (28), 391.1 (11), 372.1 (39). Mass

Spec (HR, EI): m/z 524.1835 (C32H28O7 requires 524.1819).

Synthesis of methyl 2-(4-methoxyphenyl)-2-phenyl-6-(propionyloxy)-2H- naphtho[1,2-b]pyran-5-carboxylate (17a). The title compound was synthesized in the same manner as that of (16a) using methyl 6-hydroxy-2-(4-methoxy-phenyl)-2-phenyl- 2H-naphtho[1,2-b]pyran-5-carboxylate (17) and propionyl chloride. The product was obtained as a pale pink solid (66 mg, 80%) after purification by column 1 chromatography (silica gel, diethyl ether/hexane, 1:1). H NMR (400 MHz, d6-acetone)

: 1.25 (t, J 7.3 Hz, 3H, propionyl-CH3), 2.75 (q, J 7.3 Hz, 2H, propionyl-CH2), 3.73 (s,

3H, ArOCH3), 3.91 (s, 3H, COOCH3), 6.46 (d, J 9.9 Hz, 1H, pyran-H), 6.87 (apparent d, J 8.8 Hz, 2H, ArH), 6.96 (d, J 9.9 Hz, 1H, pyran-H), 7.24 - 7.28 (m, 1H, ArH), 7.33 - 7.37 (m, 2H, ArH), 7.46 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.55 - 7.62 (m, 3H, ArH), 7.65 - 7.69 (m, 1H, ArH) 7.80 (d, J 8.4 Hz, 1H, ArH), 8.44 (d, J 8.4 Hz, 1H, 13 ArH) ppm. C NMR (100 MHz, d6-acetone) : 8.7, 27.1, 52.2, 54.9, 82.9, 113.7, 113.8, 120.2, 121.2, 122.4, 122.9, 126.5, 126.7, 127.7, 127.8, 128.0, 128.2 128.3, 128.5, 128.4, 136.8, 139.8, 145.3, 146.1, 159.6, 165.7 172.4 ppm. Mass Spec (EI): m/z ([M]+ 22%), 438.1 (55), 406.1 (100), 377.1 (30), 361.1 (14), 298.1 (14), 289.1 (14), 78.0 (18), 63.1

(22), 57.1 (23). Mass Spec (HR, EI): m/z 494.1716 (C31H26O6 requires 494.1729).

Synthesis of methyl 6-methoxy-2-(4-methoxyphenyl)-2-(4-(3-(propionyloxy)- propoxy)phenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (18a). The title compound was synthesized in the same manner as that of (16a) using methyl 6-methoxy-2-(4-(3- hydroxypropoxy)phenyl)-2-(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (18) and propionyl chloride. The product was obtained as a red solid (138 mg, 92%) after purification by column chromatography (silica gel, ethyl acetate/hexane, 1:1). 1H

NMR (400 MHz, d6-benzene) : 0.93 (t, J 7.6 Hz, 3H, propionyl-CH3), 1.71 (quintet, J

6.3 Hz, 2H, CH2CH2CH2), 1.98 (q, J 7.6 Hz, 2H, propionyl-CH2), 3.22 (s, 3H,

ArOCH3), 3.51 - 3.55 (overlapping t, J 6.3 Hz, 2H, CH2OCO and s, 3H, ArOCH3), 3.68

(s, 3H, COOCH3), 4.07 (t, 2H, J 6.3 Hz, OCH2CH2CH2), 6.05 (d, J 9.9 Hz, 1H, pyran- H), 6.68 - 6.73 (m, 4H, ArH), 6.93 (d, J 9.9 Hz, 1H, pyran-H), 7.15 - 7.20 (m, 1H, ArH), 7.24 - 7.28 (m, 1H, ArH), 7.48 - 7.52 (m, 4H, ArH), 7.96 (d, J 8.4 Hz, 1H, ArH), 13 8.47 (d, J 8.4 Hz, 1H, ArH) ppm. C NMR (400 MHz, d6-benzene) : 9.6, 27.8, 29.2,

165 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

52.2, 55.1, 61.5, 63.5, 64.8, 83.5, 114.1, 114.3, 114.8, 121.7, 121.7, 123.2, 123.6, 127.4, 127.5, 127.7, 129.1, 129.2, 129.2, 129.8, 137.7, 138.0, 145.3, 149.2, 159.1, 160.1, 167.9, 173.8 ppm. Mass Spec (EI): m/z 582.2 ([M]+ 50%), 550.2 (18), 435.1 (15), 375

(11). Mass Spec (HR, EI): m/z 582.2239 (C35H34O8 requires 582.2254).

Synthesis of methyl 6-methoxy-2,2-bis(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran -5-carboxylate (18c). The title compound was synthesized in the same manner15,30 as that of methyl 6-methoxy-2-(4-(3-hydroxypropoxy)phenyl)-2-(4-methoxyphenyl)-2H- naphtho[1,2-b]pyran-5-carboxylate (18), using methyl 4-hydroxy-1-methoxy-2- naphthoate (2b) and 1,1-bis(4-methoxyphenyl)prop-2-yn-1-ol (14). The product was isolated as a deep pink glassy solid (440 mg, 70%) after purification by column 1 chromatography (silica gel, dichloromethane/hexane, 1:1). H NMR (400 MHz, d6- benzene) : 3.22 (s, 6H, 2 × ArOCH3), 3.55 (s, 3H, 6-ArOCH3), 3.68 (s, 3H, COOCH3), 6.04 (d, J 9.9 Hz, 1H, pyran-H), 6.68 - 6.72 (m, 4H, ArH), 6.93 (d, J 9.9 Hz, 1H, pyran- H), 7.18 - 7.20 (m, 1H, ArH), 7.24 - 7.28 (m, 1H, ArH), 7.47 - 7.51 (m, 4H, ArH), 7.96 13 (d, J 8.4 Hz, 1H, ArH), 8.47 (d, J 8.4 Hz, 1H, ArH) ppm. C NMR (100 MHz, d6- benzene) : 52.2, 55.1, 63.5, 83.6, 114.0, 114.3, 121.7, 121.7, 123.2, 123.6, 127.4, 127.5, 127.7, 129.2, 129.2, 129.9 137.8, 145.3, 149.2, 160.0, 167.9 ppm. Mass Spec (EI): m/z 482.2 ([M]+ 100%), 467.1 (16), 450.1 (55), 435.1 (93), 421.1 (15), 407.1 (34),

375.1 (37), 342.1 (23), 225.1 (33). Mass Spec (HR, EI): m/z 482.1720 (C30H26O6 requires 482.1729).

Synthesis of 3-(propionyloxy)propyl 9-methoxy-2,2-bis(4-methoxyphenyl)-2H- naphtho[1,2-b]pyran-5-carboxylate (19a). The title compound was synthesized in the same manner as that of (16a) using 3-hydroxypropyl 9-methoxy-2,2-bis(4- methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (19) and propionyl chloride. The product was obtained as a pale pink glassy solid (106 mg, 85%) after purification by column chromatography (silica gel, ethyl acetate/hexane, 1:1). 1H NMR (400 MHz, d6-acetone) : 1.06 (t, J 7.6 Hz, 3H, propionyl-CH3), 2.14 (quintet, J 6.3 Hz, 2H,

CH2CH2CH2), 2.31 (q, J 7.6 Hz, 2H, propionyl-CH2), 3.75 (s, 6H, 2 × ArOCH3), 3.98

(s, 3H, COOCH3), 4.27 (t, J 6.3 Hz, 2H, CH2CH2CH2), 4.42 (t, J 6.3 Hz, 2H,

CH2CH2CH2) 6.39 (d, J 10.0 Hz, 1H, pyran-H), 6.84 - 6.92 (m, 4H, ArH), 7.21 (dd, J 8.9 Hz, J 2.6 Hz, 1H, ArH), 7.43 - 7.51 (m, 4H, ArH), 7.68 - 7.70 (overlapping d, J 10.0 Hz, 1H, pyran-H and d, J 2.6 Hz, 1H, ArH), 7.86 (d, J 8.9 Hz, 1H, ArH), 8.11 (s, 1H, 13 ArH) ppm. C NMR (100 MHz, d6-acetone) : 10.1, 28.5, 56.3, 56.7, 62.5, 63.2, 83.6,

166 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

101.9, 115.0, 117.5, 121.4, 123.6, 123.8, 126.2, 129.6, 129.6, 129.7, 129.8, 130.7, 132.4, 138.7, 149.1, 160.8, 161.5, 168.0, 175.1 ppm. Mass Spec (EI): m/z 582.3 ([M]+ 50%), 525.3 (10), 475.2 (13), 467.2 (30), 450.2 (100), 422.2 (49), 419.2 (20), 225.1

(20). Mass Spec (HR, EI): m/z 526.1966 (C35H34O8 requires 582.2254).

Synthesis of methyl 9-methoxy-2,2-bis(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran- 5-carboxylate (19c).The title compound was synthesized in the same manner as that of 3-hydroxypropyl 9-methoxy-2,2-bis(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran-5- carboxylate (19) using methyl 4-hydroxy-6-methoxy-2-naphthoate (6a) and 1,1-bis(4- methoxyphenyl)prop-2-yn-1-ol (14). The product was obtained as a pale pink solid (86 mg, 66%) after purification by column chromatography (silica gel, ethyl acetate/hexane, 1 1:1). H NMR (400 MHz, d6-acetone) : 3.77 (s, 6H, 2 × ArOCH3), 3.90 (s, 3H, 9-

ArOCH3), 3.98 (s, 3H, COOCH3), 6.39 (d, J 10.0 Hz, 1H, pyran-H), 6.84 - 6.92 (m, 4H, ArH), 7.21 (dd, J 8.9 Hz, J 2.6 Hz, 1H, ArH), 7.43 - 7.51 (m, 4H, ArH), 7.66 - 7.71 (overlapping d, J 10.0 Hz, 1H, pyran-H and d, J 2.6 Hz, 1H, ArH), 7.86 (d, J 8.9 Hz, 13 1H, ArH), 8.06 (s, 1H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 55.0, 56.3, 56.7, 83.6, 101.9, 115.0, 117.4, 121.4, 123.5, 123.7, 126.2, 129.6, 129.70, 129.8, 130.8, 132.4, 138.7, 149.1, 160.8, 161.5, 168.5 ppm. Mass Spec (EI): m/z 482.2 ([M]+ 100%), 467.2 (29), 450.2 (65), 419.2 (32), 375.2 (46), 342.1 (15), 225.1 (16). Mass Spec (HR,

EI): m/z 482.1719 (C30H26O6 requires 482.1729).

Synthesis of 3-(propionyloxy)propyl 9-methoxy-2-(4-methoxyphenyl)-2-phenyl- 2H-naphtho[1,2-b]pyran-5-carboxylate (20a). The title compound was synthesized in the same manner as that of (16a) using 3-hydroxypropyl 9-methoxy-2-(4- methoxyphenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (20) and propionyl chloride. The product was obtained as a clear glassy solid (94 mg, 77%) after purification by column chromatography (silica gel, ethyl acetate/hexane, 1:1). 1H NMR

(400 MHz, d6-acetone) : 1.05 (t, J 7.6 Hz, 3H, propionyl-CH3), 2.13 (quintet, J 6.3 Hz,

2H, CH2CH2CH2), 2.30 (q, J 7.6 Hz, 2H, propionyl-CH2), 3.73 (s, 3H, ArOCH3), 3.99

(s, 3H, 9-ArOCH3), 4.26 (t, J 6.3 Hz, 2H, CH2CH2CH2), 4.42 (t, J 6.3 Hz, 2H,

CH2CH2CH2), 6.43 (d, J 10.0 Hz, 1H, pyran-H), 6.86 (d, J 8.8 Hz, 2H, ArH), 7.20 - 7.39 (m, 4H, ArH), 7.48 - 7.57 (m, 4H, ArH), 7.68 - 7.71 (overlapping m, 2H, Ar-H and d, J 10.0 Hz, pyran-H), 7.86 (d, J 8.8 Hz, 1H, ArH), 8.10 (s, 1H, ArH) ppm. 13C NMR

(100 MHz, d6-acetone) : 8.7, 27.1, 28.3, 54.8, 55.3, 61.1, 61.8, 82.3, 100.5, 113.7, 116.1, 120.1, 122.4, 122.4 124.9, 126.7, 127.6, 128.3, 128.3, 128.4, 128.4, 129.1, 131.1,

167 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

137.0, 145.5, 147.7, 159.5, 160.2, 166.5, 173.8 ppm. Mass Spec (EI): m/z 496.2 ([M]+ 20%), 437.1 (15), 420.1 (100), 392.2 (32), 210.1 (10), 115.1 (53). Mass Spec (HR, EI): m/z 552.2137 (C34H32O7 requires 552.2148).

Synthesis of methyl 9-methoxy-2-(4-methoxy-phenyl)-2-phenyl-2H-naphtho[1,2- b]pyran-5-carboxylate (20c). The title compound was synthesized in the same manner as (16) and (17) using methyl 4-hydroxy-6-methoxy-2-naphthoate (6a) and 1-(4- methoxy-phenyl)-1-phenylprop-2-yn-1-ol (15). The product was obtained as a white solid (170 mg, 30%) after purification by column chromatography (silica gel, 1 dichloromethane/hexane, 2:3). H NMR (400 MHz, d6-acetone) : 3.73 (s, 3H,

ArOCH3), 3.89 (s, 3H, 9-ArOCH3), 3.95 (s, 3H, COOCH3), 6.43 (d, J 10.0 Hz, 1H, pyran-H), 6.86 (d, J 8.8 Hz, 2H, ArH), 7.20 - 7.27 (m, 2H, ArH), 7.32 - 7.36 (m, 2H, ArH), 7.48 (d, J 8.8 Hz, 2H, ArH), 7.57 (d, J 8.0 Hz, 2H, ArH), 7.68 - 7.71 (overlapping m, 2H, Ar-H and d, J 10.0 Hz, pyran-H), 7.86 (d, J 8.8 Hz, 1H, ArH), 8.06 (s, 1H, ArH) 13 ppm. C NMR (400 MHz, d6-acetone) : 52.4, 55.6, 56.0, 83.0, 101.2, 114.4, 116.8, 120.8, 123.0, 123.1, 125.6, 127.4, 128.3, 129.0, 129.0, 129.1, 129.1, 129.86, 131.8, 137.7, 146.2, 148.4, 160.2, 160.9, 167.8 ppm. Mass Spec (EI): m/z 452.2 ([M]+ 64%), 437.1 (23), 420.1 (100), 391.1 (25), 375.1 (38), 345.1 (20), 312 (13). Mass Spec (HR,

EI): m/z 452.1614 (C29H24O5 requires 452.1624).

Synthesis of 2-(propionyloxy)ethyl 2,2-bis(4-methoxyphenyl)-6-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (21a). The title compound was synthesized in the same manner as that of (16a) using 2-hydroxyethyl 2,2-bis(4-methoxyphenyl)-6-phenyl- 2H-naphtho[1,2-b]pyran-5-carboxylate (21) and propionyl chloride. The product was obtained as a pink foamy solid (0.532 g, 97%) after purification by column 1 chromatography (silica gel, ethyl acetate/hexane, 3:2). H NMR (200MHz, d6-acetone)

: 1.07 (t, J 7.5 Hz, 3H, propionyl-CH3), 2.31 (q, J 7.5 Hz, 2H, propionyl-CH2), 3.77 (s,

6H, 2 × ArOCH3), 3.98 (m, 2H, CH2CH2), 4.19 (m, 2H, CH2CH2), 6.44 (d, J 10.0 Hz, 1H, pyran-H), 6.84 (d, J 10.0 Hz, 1H, pyran-H), 6.92 (d, J 8.9 Hz, 4H), 7.28 - 7.33 (m, 2H, ArH), 7.45 - 7.52 (m, 9H, ArH), 7.57 - 7.65 (m, 1H, ArH), 8.46 (m, 1H, ArH) ppm. 13 C NMR (50MHz, d6-acetone) : 10.3, 28.6, 56.5, 63.4, 64.5, 84.7, 114.2, 115.3, 122.2, 123.8, 126.9, 128.5, 128.7, 129.1, 129.4, 129.8, 129.9, 130.6, 131.3, 132.2, 132.4, 134.5, 138.8, 139.6, 149.2, 161.0, 169.4, 175.1 ppm. Mass Spec (EI): m/z 614.3 ([M]+ 38%), 513.2 (12), 496.2 (79), 467.2 (17), 407.1 (13). Mass Spec (HR, EI): m/z 614.2304

(C39H34O7 requires 614.2305).

168 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Synthesis of 3,3-bis(4-methoxyphenyl)-13-(propionyloxy)ethyl-indeno[2,1- f]naphtha[1,2-b]pyran (22a). The title compound was synthesized in the same manner as that of (16a) using 3,3-bis(4-methoxyphenyl)-13-hydroxy-indeno[2,1-f]naphtho[1,2- b]pyran (22) and propionyl chloride. The product was obtained as a pale mauve solid (100 mg, 80%) after crystallisation from diethyl ether/hexane. 1H NMR (200MHz,

CDCl3) : 1.26 (t, J 7.6 Hz, 3H, propionyl-CH3), 2.49 (q, J 7.6 Hz, 2H, propionyl-CH2),

3.76 (s, 6H, 2 × ArOCH3), 6.23 (d, J 9.9 Hz, 1H, pyran-H), 6.77 - 6.87 (m, 5H, ArH), 7.04 (s, 1H, ArH), 7.19 - 7.26 (m, 1H, ArH), 7.38 - 7.62 (m, 8H, ArH), 8.08 (d, J 7.8 13 Hz, 1H, ArH), 8.41 - 8.54 (m, 2H, ArH) ppm. C NMR (50MHz, CDCl3) : 9.4, 28.0, 55.2, 73.8, 83.0, 113.1, 113.4, 113.5, 119.8, 122.0, 123.3, 123.8, 125.4, 125.6, 125.8, 126.0, 127.3, 128.1, 128.2, 129.1, 129.2, 129.4, 129.7, 136.6, 137.0, 137.1, 142.3, 142.7, 148.3, 158.9, 175.0 ppm. Mass Spec (EI): m/z 554.3 ([M]+ 53%), 480.2 (100), 463.2 (26), 449.2 (87), 372.2 (40) 357.1 (12) 240.3 (67) Mass Spec (HR, EI): m/z

554.2085 (C37H30O5 requires 554.2093).

Poly(dimethyl siloxane)-conjugated naphthopyrans

(For reference with regards to PDMS numbering)

Synthesis of carboxylic acid terminated poly(dimethylsiloxane), n = 12.6. Hydroxy end-terminated poly(dimethylsiloxane) (25 g, ca. 0.0221 mol) and succinic anhydride

(2.65 g, 0.0265 mol) were added to dry CH2Cl2 (ca. 40 mL) under nitrogen. Triethylamine (3.35 g, 4.6 mL, 0.033 mol) was then added in one portion, the mixture stirred at room temperature for 30 minutes followed by heating at 35 °C for 1 hour. Polyethylene glycol methyl ether (3.86 g, 0.011 mol) was added and the mixture stirred for an additional 30 minutes at 35 °C. Hexane (ca. 40 mL) was then added, the mixture washed with several portions of 1M HCl then dried with anhydrous MgSO4. The solvent was removed under vacuum giving the pure product as a colourless oil (26.34 g, 97%). 1 H NMR (400 MHz, CDCl3) : 0.04 - 0.08 (m, av. 80H, SiCH3), 0.50 - 0.55 (m, 4H,

CH2-4,5), 0.88 (t, J 7.0 Hz, 3H, CH3-1), 1.26 - 1.36 (m, 4H, CH2-2,3), 1.57 - 1.65 (m,

2H, CH2-6), 2.68 (br s, 4H, CH2-10,11), 3.42 (t, J 7.3 Hz, 2H, CH2-7), 3.63 (t, J 4.8 Hz,

169 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

2H, CH2-8), 4.25 (t, J 4.8 Hz, 2H, CH2-9) ppm. Refer to figure above for corresponding 1 numbering system used for CH2 H NMR assignments.

Synthesis of succinoyl chloride terminated poly(dimethylsiloxane), n = 12.6. Carboxylic acid terminated poly(dimethylsiloxane) (1.0 g, ca. 0.811 mmol) was dissolved in dry dichloromethane (10 mL) under nitrogen and 1 small drop DMF added. To the mixture was added oxalyl chloride (0.41 g, 0.28 mL, 3.24 mmol) in one portion. The mixture was stirred at ambient temperature for no more than 30 minutes whilst maintaining a slow nitrogen flow above the reaction by means of a syringe needle through a rubber septum. The solvent and excess reagents were removed under vacuum with residual traces of oxalyl chloride removed with the aid of 1,2-dichloroethane. The acid chloride product was used immediately. Analysis by 1H NMR in d-chloroform 1 showed quantitative conversion. H NMR (400 MHz, CDCl3) : 0.04 - 0.08 (m, av.

80H, SiCH3), 0.50 - 0.55 (m, 4H, CH2-4,5), 0.88 (t, J 7.0 Hz, 3H, CH3-1), 1.26 - 1.36

(m, 4H, CH2-2,3), 1.57 - 1.65 (m, 2H, CH2-6), 2.72 (t, J 6.6 Hz, 2H, CH2-10), 3.22 (t, J

6.6 Hz, 2H, CH2-11), 3.42 (t, J 7.0 Hz, 2H, CH2-7), 3.63 (t, J 4.8 Hz, 2H, CH2-8), 4.26

(t, J 4.8 Hz, 2H, CH2-9) ppm. Refer to figure above for corresponding numbering 1 system used for CH2 H NMR assignments.

Synthesis of methyl 2,2-bis(4-methoxyphenyl)-6-(butyl(PDMS)propyloxyethoxy- succinoyloxy)-2H-naphtho[1,2-b]pyran-5-carboxylate (16b), n = 13.6. Methyl 6- hydroxy-2,2-bis(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (16) (0.25 g, 0.534 mmol) was dissolved into dry dichloromethane (10 mL) followed by the addition of triethylamine (119 mg, 0.16 mL, 1.17 mmol), under an atmosphere of argon. Mono- succinoyl chloride end-functionalised poly(dimethylsiloxane), synthesized as described above, was then added dropwise (0.485 mmol) and the mixture was left to stir at room temperature for 1 hour. The solvent was then removed under vacuum, the residue re- dissolved in diethyl ether/hexane (1:1) and the mixture filtered through a plug of silica gel. The solvent was removed and the remaining oily residue was purified by column

170 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

chromatography (silica gel, CH2Cl2/petroleum ether, 4:1) to give the pure PDMS 1 conjugate as a viscous red oil (759 mg, 80%). H NMR (400 MHz, d6-acetone) : 0.07 -

0.13 (m, SiCH3), 0.57 (m, 4H, CH2-4,5), 0.89 (t br, J 7.0 Hz, 3H, CH3-1), 1.35 (m, 4H,

CH2-2,3), 1.59 (m, 2H, CH2-6), 2.78 (m, 2H, CH2-10 overlap with H2O and HDO signals), 3.04 (t, J 6.5 Hz, 2H, CH2-11), 3.41 (t, J 6.8 Hz, 2H, CH2-7), 3.62 (t, J 5.0 Hz,

2H, CH2-8), 3.75 (s, 6H, 2 × ArOCH3), 3.95 (s, 3H, COOCH3), 4.23 (t, J 5.0 Hz, 2H,

CH2-9), 6.40 (d, J 10 Hz, 1H, pyran-H), 6.88 (d, J 8.8 Hz, 4H, ArH), 6.96 (d, J 10 Hz, 1H, pyran-H), 7.44 (d, J 8.8 Hz, 4H, ArH), 7.59 (t, J 7.5 Hz, 1H, ArH), 7.66 (t, J 7.5 Hz, 1H, ArH), 7.94 (d, J 8.5 Hz, 1H, ArH), 8.40 (d, J 8.5 Hz, 1H, ArH) ppm. Refer to 1 figure above for corresponding numbering system used for CH2 H NMR assignments of (16b).

Synthesis of ethyl 2-(4-methoxyphenyl)-2-phenyl-6-(butyl(PDMS)propyloxyethoxy -succinoyloxy)-2H-naphtho[1,2-b]pyran-5-carboxylate (17b) n = 11.7. The title photochromic PDMS oil was synthesized in the same manner as that of (16b) using methyl 6-hydroxy-2-(4-methoxy-phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5- carboxylate (17) and mono-succinoyl chloride end-functionalised poly(dimethylsiloxane). The product was obtained as viscous orange oil (345 mg, 86%) after purification by column chromatography (silica gel, diethyl ether/hexane, 1:3). 1H

NMR (400 MHz, d6-acetone) : 0.07 - 0.12 (m, SiCH3), 0.57 (m, 4H, CH2-4,5), 0.88

(br t, J 6.9 Hz, 3H, CH3-1), 1.35 (m, 4H, CH2-2,3), 1.59 (m, 2H, CH2-6), 2.78 (m 2H,

CH2-10 overlap with H2O and HDO signals), 3.04 (t, J 6.9 Hz, 2H, CH2-11), 3.41 (t, J

6.9 Hz, 2H, CH2-7), 3.62 (t, J 5.1 Hz, 2H, CH2-8), 3.74 (s, 3H, ArOCH3), 3.95 (s, 3H,

COOCH3), 4.23 (t, J 5.1 Hz. CH2-9), 6.46 (d, J 9.9 Hz, 1H, pyran-H), 6.87 (apparent d, J 8.8 Hz, 2H, ArH), 6.96 (d, J 9.9 Hz, 1H, pyr-CH), 7.24 - 7.28 (m, 1H, ArH), 7.33 - 7.37 (m, 2H, ArH), 7.46 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.55 - 7.62 (m, 3H, ArH), 7.65 - 7.69 (m, 1H, ArH) 7.80 (d, J 8.4 Hz, 1H, ArH), 8.44 (d, J 8.4 Hz, 1H, 1 ArH) ppm. Refer to figure above for corresponding numbering system used for CH2 H NMR assignments of (17b). 171 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Synthesis of methyl 6-methoxy-2-(4-methoxyphenyl)-2-(4-(3-(butyl(PDMS)propyl oxyethoxy-succinoylpropoxy)phenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (18b) n = 12.6. The title photochromic PDMS oil was synthesized in the same manner as that of (16b) using methyl 6-methoxy-2-(4-(3-hydroxypropoxy)phenyl)-2-(4- methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (18) and mono-succinoyl chloride end-functionalised poly(dimethylsiloxane). The product was obtained as viscous deep pink oil (571 mg, 90%) after purification by column chromatography 1 (silica gel, diethyl ether/hexane, 1:1). H NMR (400 MHz, d6-acetone) : 0.07 - 0.13

(m, SiCH3), 0.57 - 0.61 (m, 4H, CH2-4,5), 0.89 (t br, J 6.9 Hz, 3H, CH3-1), 1.34 - 1.38

(m, 4H, CH2-2,3), 1.56 - 1.64 (m, 2H, CH2-6), 2.07 (m, 2H, CH2-13 overlap with solvent signals), 2.60 (s, 4H, CH2-10,11), 3.40 (t, J 6.8 Hz, 2H, CH2-7), 3.57 (t, J 4.8

Hz, 2H, CH2-8), 3.76 (s, 3H, CH3OAr), 3.92 (s, 3H, 6-ArOCH3), 3.97 (s, 3H,

COOCH3), 4.06 (t, J 6.2 Hz, 2H, CH2-12), 4.15 (t, J 5.1 Hz, 2H, CH2-9), 4.23 (t, J 6.2

Hz, 2H, CH2-14), 6.40 (d, J 9.9 Hz, 1H, pyran-H), 6.75 (d, J 9.9 Hz, 1H, pyran-H), 6.90 (t, J 8.8 Hz, 4H, ArH), 7.44 (d, J 8.8 Hz, 4H), 7.57 - 7.65 (m, 2H, ArH), 8.05 (d, J 8.8 Hz, 1H, ArH), 8.38 (d, J 8.8 Hz, 1H, ArH) ppm. Refer to figure above for 1 corresponding numbering system used for CH2 H NMR assignments of (18b).

Synthesis of 3-(butyl(PDMS)propyloxyethoxy-succinoyloxy)propyl-methoxy-2,2- bis(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran-5-carboxylate (19b) n = 13. The title photochromic PDMS oil was synthesized in the same manner as that of (16b) using 3-hydroxypropyl 9-methoxy-2,2-bis(4-methoxyphenyl)-2H-naphtho[1,2-b]pyran-5- carboxylate (19) and mono-succinoyl chloride end-functional poly(dimethylsiloxane). The product was obtained as viscous pale pink oil (350 mg, 75%) after purification by 1 column chromatography (silica gel, diethyl ether/hexane, 1:1). H NMR (400 MHz, d6- 172 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

acetone) : 0.09 - 0.13 (m, SiCH3), 0.56 - 0.60 (m, 4H, CH2-4,5), 0.90 (br t, J 6.7 Hz,

3H, CH2-1), 1.30 - 1.38 (m, 4H CH2-2,3), 1.56 - 1.64 (m, 2H, CH2-6), 2.15 (p, J 6.3 Hz,

2H, CH2-13), 2.62 (s, 4H, CH2-10,11), 3.40 (t, J 6.8 Hz, 2H, CH2-7), 3.60 (t, J 5.0 Hz,

2H, CH2-8), 3.75 (s, 6H, 2 × ArOCH3), 3.98 (s, 3H, 9-ArOCH3), 4.16 (t, J 5.0 Hz. CH2-

9), 4.30 (t, J 6.3 Hz, 2H, CH2-12), 4.43 (t, J 6.3 Hz, 2H, CH2-14), 6.38 (d, 1H, J 10.0 Hz, pyran-H), 6.86 - 6.90 (m, 4H, ArH), 7.21 (dd, 1H, J 8.9 Hz, J 2.5 Hz, ArH), 7.46 - 7.49 (m, 4H, ArH), 7.66 - 7.69 (overlapping d, 1H J 10.0 Hz, pyran-H and br d, 1H, J 2.5 Hz, ArH), 7.86 (d, 1H, J 8.9 Hz, ArH), 8.11 (s, 1H, ArH) ppm. Refer to figure above 1 for corresponding numbering system used for CH2 H NMR assignments of (19b).

Synthesis of 3-(butyl(PDMS)propyloxyethoxy-succinoyloxy)propyl 9-methoxy-2- (4-methoxyphenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (20b) n = 12.9. The title photochromic PDMS oil was synthesized in the same manner as that of (16b) using 3-hydroxypropyl 9-methoxy-2-(4-methoxyphenyl)-2-phenyl-2H-naphtho[1,2- b]pyran-5-carboxylate (20) and mono-succinoyl chloride end-functionalised poly(dimethylsiloxane). The product was obtained as viscous peach coloured oil (457 mg, 85%) after purification by column chromatography (silica gel, diethyl ether/hexane, 1 1:1). H NMR (400 MHz, d6-acetone) : 0.07 - 0.12 (m, SiCH3), 0.55 - 0.60 (m, 4H,

CH2-4,5), 0.88 (br t, J 6.7 Hz, 3H, CH2-1), 1.26 - 1.37 (m, 4H CH2-2,3), 1.55 - 1.63 (m,

2H, CH2-6), 2.13 (p, J 6.3 Hz, 2H, CH2-13), 2.61 (s, 4H, CH2-10,11), 3.40 (t, J 6.9 Hz,

2H, CH2-7), 3.58 (t, J 5.1 Hz, 2H, CH2-8), 3.73 (s, 3H, ArOCH3), 3.99 (s, 3H, 9-

ArOCH3), 4.16 (t, J 5.1 Hz. CH2-9), 4.29 (t, J 6.3 Hz, 2H, CH2-12), 4.42 (t, J 6.3 Hz,

2H, CH2-14), 6.43 (d, 1H, J 10.0 Hz, pyran-H), 6.86 (d, 2H, J 8.8 Hz, ArH), 7.20 - 7.39 (m, 4H, ArH), 7.48 - 7.57 (m, 4H, ArH), 7.68 - 7.71 (m, 2H, ArH and J 10.0 Hz, pyran- H), 7.86 (d, 1H, J 8.8 Hz, ArH,), 8.10 (s, 1H, ArH) ppm. Refer to figure above for 1 corresponding numbering system used for CH2 H NMR assignments of (20b).

173 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

Synthesis of 2,2-Bis(4-methoxyphenyl)-5-(butyl(PDMS)propyloxyethoxy-succinoyl oxy-ethoxycarbonyl)-6-phenyl-2H-naphtho[1,2-b]pyran (21b) n = 13.1. The title photochromic PDMS oil was synthesized in the same manner as that of (16b) using 2- hydroxyethyl 2,2-bis(4-methoxyphenyl)-6-phenyl-2H-naphtho[1,2-b]pyran-5- carboxylate (21) and mono-succinoyl chloride end-functionalised poly(dimethylsiloxane). The product was obtained as viscous pink oil (667 mg, 82%) after column chromatography (silica gel, diethyl ether/hexane, 1:1). 1H NMR (400

MHz, d6-acetone) : 0.09 - 0.13 (m, SiCH3), 0.59 (m, 4H, CH2-4,5), 0.90 (t, J 6.9 Hz,

3H, CH3-1), 1.37 (m, 4H, CH2-2,3), 1.59 (m, 2H, CH2-6), 2.62 (s, 4H, CH2-10,11), 3.38

(t, J 6.8 Hz, 2H, CH2-7), 3.54 (t, J 5.0 Hz, 2H, CH2-8), 3.77 (s, 6H, ArOCH3), 3.99 (m,

2H, CH2-13), 4.14 (t, J 5.0 Hz, 2H, CH2-9), 4.19 (m, 2H, CH2-12), 6.45 (d, J 10.0 Hz, 1H, pyran-H), 6.85 (d, J 10.0 Hz, 1H, pyran-H), 6.92 (d, J 8.9, 4H, ArH), 7.32 (m, 2H, ArH), 7.44 - 7.50 (m, 9H, ArH), 7.61 (m, 1H, ArH), 8.46 (d, J 8.4 Hz, 1H, ArH) ppm. 1 Refer to figure above for corresponding numbering system used for CH2 H NMR assignments of (21b).

Synthesis of 3,3-bis(4-methoxyphenyl)-13-(butyl(PDMS)propyloxyethoxy-succinoyl oxy)-indeno[2,1-f]naphtho[1,2-b]pyran (22b) n = 12.9. The title photochromic PDMS oil was synthesized in the same manner as that of (16b) using 3,3-bis(4- methoxyphenyl)-13-hydroxy-indeno[2,1-f]naphtho[1,2-b]pyran (22) and mono- succinoyl chloride end-functionalised poly(dimethylsiloxane). The product was obtained as a viscous dark-purple coloured oil, (528 mg, 75%) after column 1 chromatography (silica gel, chloroform/hexane, 5:4 to neat CHCl3). H NMR (400

174 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

MHz, CDCl3) : 0.04 - 0.08 (m, SiCH3), 0.52 (m, 4H, CH2-4,5), 0.88 (t, J 6.9 Hz, 3H,

CH3-1), 1.32 (m, 4H, CH2-2,3), 1.60 (m, 2H, CH2-6), 2.69 - 2.83 (m, 4H, CH2-10,11),

3.39 (t, J 7.1 Hz, 2H, CH2-7), 3.59 (t, J 4.9 Hz, 2H, CH2-8), 3.76 and 3.77 (2  s overlapping, 6H, ArOCH3), 4.25 (t, J 4.9 Hz, 2H, CH2-9), 6.23 (d, J 9.9 Hz, 1H, pyran- H), 6.81 - 6.85 (m, 5H, ArH), 7.04 (s, 1H, indeno-CH), 7.22 (t, J 7.4 Hz, 1H, ArH), 7.39 - 7.44 (m, 5H, ArH), 7.50 - 7.60 (m, 3H, ArH), 8.09 (d, J 7.8 Hz, 1H, ArH), 8.43 (d, 8.4 Hz, 1H, ArH), 8.53 (d, J 8.4 Hz, 1H, ArH) ppm. Refer to figure above for 1 corresponding numbering system used for CH2 H NMR assignments of (22b).

5.5 References

(1). Heron, B. M.; Gabbutt, C. D.; Hepworth, J. D.; Partington, S. M.; Clarke, D. A.; Corns, S. N. Rapid fading photo-responsive materials. WO 01/12619 A1, 2001. (2). Clarke, D. A.; Heron, B. M.; Gabbutt, C. D.; Hepworth, J. D.; Partington, S. M.; Corns, S. N. Neutral Colouring Photochromic 2H-Naptho[1,2-b]pyrans and Heterocyclic Pyrans. US 6,248,264 B1, 2001. (3). Clarke, D. A.; Heron, B. M.; Gabbutt, C. D.; Hepworth, J. D.; Partington, S. M.; Corns, S. N. Intense Colouring Photochromic 2H-Naphtho[1,2-b]pyrans and Heterocyclic Pyrans. WO 98/42695, 1998. (4). Kumar, A.; VanGemert, B.; Knowles, D. B. Novel substituted naphthopyrans. WO 95/16215, 1995. (5). Van Gemert, B.; Kumar, A.; Knowels, D. Mol. Cryst. Liq. Cryst. 1997, 297, 131- 138. (6). Van Gemert, B. Photochromic indeno-fused naphthopyran compounds. US 5,645,767, 1997. (7). Van Gemert, B. Novel Photochromic Indeno-fused Naphthopyrans. WO 96/14596, 1995. (8). Christie, R. M.; Hepworth, J. D.; Gabbut, C. D.; Rae, S. Dyes and Pigments 1997, 35, 4, 339-346. (9). Van Gembert, B., Benzo and Naphthopyrans (Chromenes), Chapter 3. In Organic Photochromic and Thermochromic Compounds, Crano, J.; Guglielmetti, R., Eds. Plenum Publishing, New York: 1998; Vol. 1. (10). Krongauz, V., Environmental Effects on Organic Photochromic Systems. In Photochromism: Molecules and Systems, 1st ed.; Dürr, H.; Bouas-Laurent, H., Eds. Elsevier Science Publishing House: Amsterdam, 1990; pp 793-820.

175 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

(11). Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Yee, L. H.; Lewis, D. A. Fast Fade photochromic dyes through nano-encapsulation. "Photochromic Compositions and Light transmissible articles". WO 2004/041961 A1, 2003. (12). Evans, R. A.; Such, G. K.; Malic, N.; Davis, T. P.; Lewis, D. A.; Campbell, J. A. Photochromic Compounds Comprising Polymeric Substituents and Methods for Preparation and Use Thereof. WO2006024099, 2006. (13). Evans, R. A.; Such, G. K. Aust. J. Chem. 2005, 58, 825-830. (14). Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Davis, T. P.; Such, G. K.; Yee, L. H.; Ball, G. E.; Lewis, D. A. Nature Mater. 2005, 4, 3, 249-254. (15). Gabbutt, C. D.; Heron, M. B.; Instone, A. C.; Thomas, D. A.; Partington, S. M.; Husthouse, M. B.; Gelbrich, T. Eur. J. Org. Chem. 2003, 1220-1230. (16). Tanaka, K.; Aoki, H.; Hosomi, H.; Ohba, S. Org. Lett. 2000, 2, (14), 2133-2134. (17). Zhao, W.; Carreira, E. M. Org. Lett. 2003, 5, (22), 4153 - 4154. (18). Gabbutt, C. D.; Hepworth, J. D.; Heron, M.; Thomas, D. A.; Partington, S. M. Heterocycles 2004, 63, (3), 567-582. (19). Van Gemert, B.; Bergomi, M.; Knowles, D. B. Mol. Cryst. Liq. Cryst. 1994, 246, 67-73. (20). Kumar, A.; Van Gemert, B.; Knowels, D. Mol. Cryst. Liq. Cryst. 2000, 344, 217- 222. (21). Kim, B.-K.; Deng, J.; Xiao, W.; Van Gemert, B.; Chopra, A.; Molock, F.; Mahadevan, S. Ophthalmic devices comprising photochromic materials having extended pi-conjugated systems. US 2006/0226402, 2006. (22). Hattori, T.; Nobuyuki, H.; Oi, S.; Abe, H.; Miyano, S. Tetrahedron: Assym. 1995, 6, (5), 1043-1046. (23). Asiri, A. M. J. Photochem. Photobiol. A 2003, 159, 1-5. (24). Doulut, S.; Dubuc, I.; Rodriguez, M.; Vecchini, F.; Fulcrand, H.; Barelli, H.; Checler, F.; Bourdel, E.; Aumelas, A.; Lallement, J. C.; Kitabgi, P.; Costentin, J.; Martinez, J. J. Med. Chem. 1993, 36, 1369-1379. (25). Boger, D. L.; Han, N.; Tarby, C. M.; Boyce, C. W.; Cai, H.; Jin, Q.; Kitos, P. A. J. Org. Chem. 1996, 61, 4894-4912. (26). Tanaka, K.; Sugino, T.; Toda, F. Green Chem. 2000, 2, 303-304. (27). Walters, R. W.; Van Gemert, B. Hydroxylated/Carboxylated Naphthopyrans. WO 01/70719, 2001.

176 Chapter 5. Optimizing Photochromic Performance using PDMS Conjugation. ______

(28). Aki, S.; Haraguchi, Y.; Sakikawa, H.; Ishigami, M.; Fujioka, T.; Furuta, T.; Minamikawa, J. Org. Process. Res. Dev. 2001, 5, 535-538. (29). Zeynizadeh, B.; Behyar, T. Bull. Chem. Soc. Jpn. 2005, 78, 307. (30). Gabbut, C. D.; Heron, B. M.; Instone, A. C.; Horton, P. N.; Hursthouse, M. B. Tetrahedron 2005, 61, 463-471. (31). Sriprom, W.; Néel, M.; Gabbutt, C. D.; Heron, M.; Perrier, S. J. Mater. Chem. 2007, 17, 1885-1893. (32). Van Gemert, B.; Chopra, A.; Kumar, A. Polymerizable Polyalkoxylated Naphthopyrans. WO 00/15629, 2000. (33). Edens, M.; Boerner, D.; C., R.; Chase, D. N.; Schiavelli, M. D. J. Org. Chem. 1977, 42 (21), 3403-3407. (34). Biteau, J.; Chaput, F.; Boilot, J. J. Phys. Chem. 1996, 100, 9024-9031. (35). Delbaere, S.; Luccioni-Huoze, B.; Bochu, C.; Teral, Y.; Campredon, M.; Vermeersch, G. J. Chem. Soc., Perkin Trans. 2. 1998, 1153-1157. (36). Zayat, M.; Levy, D. J. Mater. Chem. 2003, 13, 727-730. (37). Such, G. K.; Evans, R. A.; Yee, L. H.; Davis, T. P. J. Macromol. Sci. Polym. Revs. 2003, C43, (4), 547-579. (38). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2006, 39, 4, 1392-1396. (39). Malic, N.; Campbell, J. A.; Evans, R. A. Macromolecules 2008, 41, 1206-1214. (40). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2004, 37, (26), 9664- 9666. (41). Such, G. K.; Evans, R. A.; Davis, T. P. Macromolecules 2006, 39, 9562-9570. (42). Ottavi, G.; Favaro, G.; Malatesta, V. J. Photochem. Photobiol. A 1998, 115, 123- 128. (43). Delbaere, S.; Micheau, J.-C.; Vermeersch, G. J. Org. Chem. 2003, 68, 8968-8973. (44). Coelho, P. J.; Salvador, M. A.; Oliveira, M.; Carvalho, L. M. J. Photochem. Photobiol. A 2005, 172, 300-307. (45). Ercole, F.; Davis, T. P.; Evans, R. A. Macromolecules 2009, 42, (5), 1500-1511. (46). Favaro, G.; Malatesta, V.; Mazzucato, U.; Ottavi, G.; Romani, A. J. Photochem. Photobiol. A 1995, 87, 235-241.

177 6 Photochromic Behaviour within Polymer Matrices Part 1: Highly Crosslinked Networks

6.1 Introduction

Photochromism has been used in the manufacture of light transmissible articles for over two decades. Practical utility of photochromic dyes normally requires their incorporation into a matrix that is optically clear and mechanically viable. When irradiated with UV light, the photochromic transformations of dye molecules within the matrix bring about a striking colour change that fades away when the UV radiation ceases. 1,2 The use of photochromic dyes is most well known in the manufacture of spectacle lenses in which dye molecules allow radiation to be filtered out at a level that varies with the intensity of the incident UV radiation.3 Photochromic dyes are also being investigated in a range of other functional materials such as windows, automotive and aircraft windshields, coatings, optical switches, data storage and security devices.4-8 In these applications polymers are most often used as the host matrices however inorganic and hybrid materials are also attracting increasing interest.9

Figure 1. Photochromic transition between clear and coloured forms showing substituted 2,2-diaryl-2H-naphtho[1,2-b]pyran of interest to paper. (Asymmetry at quaternary carbon results in four isomers CTC (shown), TTT (shown), TTC and CTT).

For applications such as spectacles or panels, the strength, hardness and abrasion resistance of the host are critical and cannot be compromised in order to achieve more desirable rates of photochromic transformations. In previous chapters I have shown that when the dye is directly conjugated to one or two polymer tails, this can affect its local Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

environment to such a degree that the switching speed within a host matrix can be controlled in a predictable manner.10-12 Longer and more lubricating tails result in increasingly faster kinetics. Meanwhile the host matrix composition, containing the photochromic-polymer conjugate, is able to produce an optically clear lens material on curing with properties that are not compromised in order to achieve dramatic modifications to photochromic kinetics (Figure 2).13-15

Figure 2. Illustration of how the tethering of oligomers of known properties (such as Tg or viscosity) to dyes controls their switching behaviour by modifying its local environment.15

An important part of the methodology is that the photochromic molecule is chemically tethered to the polymer tail/s. The photochromic-polymer conjugates, however, do not actually end up bound to the host matrix in which they reside. They could therefore diffuse and migrate to the surface of the lens material over time, which could lead to loss of photochromic performance. One strategy to overcome this potential problem is to produce films/coatings in which the bulk material is composed entirely of the photochromic-polymer conjugate itself. For example, controlled radical polymerization techniques can be used to synthesize hard-soft block copolymers that phase separate on annealing, leaving the photochromic moieties bound within the soft phase of the material. Within a soft and lubricated environment, dyes are mobile enough to achieve fast switching, whilst the bulk material has a high enough Tg to maintain structural integrity at higher than ambient temperatures.11,16 Another approach is to chemically react a photochromic-functionalized monomer17 directly with the curable lens matrix composition (Figure 3).18 The standard lens 13 material is however a very rigid with a measured Tg of approx. 120°C and this process would fix the dye into a very restrictive environment for switching. A solution to this is to have both a lubricating tail, such as a PDMS tail, as well as a tethering moiety, such as a methacrylate group, attached to the same dye molecule. The methacrylate group cross-reacts radically with the host matrix monomers and becomes tethered in the

180 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______process to prevent mass migration of the dye. And, as a result of a vicinal lubricating tail, the dye becomes positioned within a local environment that allows it be mobile enough to achieve fast switching.19

Figure 3. Thermally curable lens matrix monomers (4:1 mass ratio of top to bottom monomer in standard lens formulation).

The purpose of this work was to continue this approach with a view to understanding how a naphthopyran dye is affected by tethering to a crosslinked network structure. In this first section several photochromic momomers were reacted within the highly crosslinked network that makes up the lens matrix. This included structures that had either one or two reactive moieties on opposite sides of the molecule and separated from the dye by various lengths of spacers. In the next chapter some of the photochromic monomers are used as crosslinkers in hyperbranched polymers and their photochromic properties compared to the network structures presented here.

6.2 Results and Discussion

The standard lens formulation comprises 4:1 weight ratio of oligoethylene dimethacrylates shown in Figure 3 above. The mixture is thermally cured in the presence of AIBN (azobis(isobutyyronitrile, 0.4%) to produce a highly crosslinked, three-dimensional polymer network structure. Photochromic lens samples are produced by mixing into the mixture equivalent amounts (1.5 x 10-7 mol/gram of matrix monomers) of photochromic compound. Curing of the monomer mixture is then carried out in a mould and enclosed between two glass plates to produce photochromic test samples of equivalent thickness. The curing conditions (16 hours, at 80 C) and high amount of initiator in the mixture is to promote a high conversion of monomer to polymer.

181 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

6.2.1 Photochromic Kinetics

An initially colourless photochromic sample becomes highly coloured when irradiated with UV light and spontaneously decolourizes in the dark upon cessation of incident light. The back reaction occurs thermally as the photochromic open form undergoes ring closure. Whilst monitoring absorption density with time at the max of the coloured form (500 nm), the sample is initially UV-irradiated for 1000 seconds and then the disappearance of the coloured form is followed in the dark at 20 C for a further 4,800 seconds. The collected decay data of each sample is fitted to the following biexponential equation to obtain the thermal ring-closure rate constants:    k1t  k 2t  A(t) A1e A2e Ath where A(t) is the optical density at max of the open form; A1 and A2 are the contributions to the initial optical density (colourability), A0; k1 and k2 are exponential decay rate constants of fast and slow components respectively and Ath is the residual colouration (offset). The A0 value is in fact the absorbance level attained after 1000 seconds of continuous irradiation. The T1/2 value is the time taken for the sample to fade to half of the A0 value and is insightful for comparing overall kinetics. The equation20,21 has been used frequently to represent and compare the decolouration behaviour of both spirooxazines and naphthopyrans within solid media16,22 and has consistently fitted our decolouration curves with correlation coefficients (R) greater that 0.99.10-15, As discussed in previous work10 and as depicted in Figure 1, exposure of the naphthopyran closed form (CF) to continuous UV irradiation results in a distribution of coloured merocyanine isomers. Two main classes of open isomers can be distinguished: short-lived trans-cis (TC) geometrical isomers and a longer-lived and minor trans-trans (TT) population. The latter reverts to the closed form through a two step process with the TC isomers being intermediates (ie. TTTCCF).23,24 In solution the thermal decolouration behaviour can be attributed to these two classes of open isomers decaying with different first-order rate constants, k1 and k2. For some naphthopyrans the TT isomer population that is formed can remain stable in the dark at ambient temperature. In this instance the decolouration data can be fitted to monoexponential decay plus a residual absorbance term which represents the stable isomer population.

182 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

The lens matrix is a complex network structure with an inhomogenous consistency. The structure is characterized by the presence of network strands with dangling, oxygen and radical capped chain-ends, entanglements, crosslinking junctions, all resulting in a complex topology. Compared to solution, it can be considered to be made up of a distribution of non-equivalent regions. Photochromic fade kinetics within the lens can therefore be complicated by the disperse nature of the dye’s environment. The separated constants, k1 and k2, in the equation above, along with their allocated contributions to initial optical density, are therefore considered empirical values which merely represent fast and slow components of the fade. Table 1 displays the photochromic structures, 1 - 13, that were tested within a lens matrix. To eliminate the possibility of different electronic substitution patterns influencing photochromic properties, all the dyes tested in this study were built on the same base structure. These red-colouring derivatives were easily prepared from hydroxylated naphthopyran starting materials (Figure 4) using standard acid chloride chemistry, the details of which are included in the experimental section.10-13

Figure 4. Hydroxylated naphthopyran starting materials used for synthesis of naphthopyran compounds, 1-13.

In the case of polyethylene glycol (PEG)-dye conjuagates 1-5, carboxylic acid functionalized PEG was firstly prepared from commercially available PEG derivatives by acylation of its OH terminus with succinic anhydride. This was either PEG methyl ether, where Mn = 750 g/mol and n = ~17; Mn = 550 g/mol and n = ~12 or PEG methacrylate where Mn = 526 g/mol and n = ~10. The oligomeric products were able to be purified by chromatography and, in the case of 2 and 3, fractionation allowed some separation of average chain length.

183 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

Table 1. Structures of naphthopyrans tested in lens matrix.

n(vinyl) T c Structure n(EG) units a 1/2 Sample group b (s)

18 0 82.5 1

14 0 88.5 2

11 0 88.5 3

10 1 121.5 4

1 1 132.0 5

3 2 244.5 6

1 2 363.0 7

1 1 280.5 8

1 1 256.5 9

a Number of ethylene glycol units within the structure. b Number of methacrylate units c within the structure. Time taken for the initial absorbance value, A0, to decay to half its original value.

184 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

Table 1 (continued). Structures of naphthopyrans tested in lens matrix. n(vinyl) T c Structure n(EG) units a 1/2 Sample groups b (s)

0 1 241.5 10

11 1 0 130.0 (control)

12 0 0 127.5 (control)

13 - 0 120.0 (control)

a Number of ethylene glycol units within the structure. b Number of methacrylate units c within the structure. Time taken for the initial absorbance value, A0, to decay to half its original value.

6.2.2 Photochromic Behaviour within Network Structure

Samples 1-3 are PEG-dye conjugates which do not contain a polymerizable group and simply differ in the number of ethylene glycol (EG) units. Samples 4-10 contain at least one polymerizable group, either at the top, the bottom, or on both sides of the molecule. These photochromic monomers also differ in the number of EG units. Samples 11-13 are control dyes which serve as reference points for tests, allowing the direct effect of EG spacers and matrix tethering on the performance of the dye to be analyzed. Corresponding photochromic kinetic parameters are displayed in Table 2.

185 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

Table 2. Photokinetic analysis of decolouration displayed by naphthopyran samples in lens matrix.a

k k Compound A b A 1 A 2 A T (s)c 0 1 (min-1) 2 (min-1) th 1/2 1 0.88 0.6944 0.8349 0.0661 0.090 0.22 82.5 2 0.94 0.6763 0.8072 0.0740 0.0830 0.23 88.5 3 0.93 0.6630 0.7992 0.0761 0.0850 0.24 88.5 4 0.75 0.5942 0.6965 0.1284 0.0700 0.24 121.5 5 0.70 0.5738 0.7035 0.1482 0.0695 0.25 132.0 6 0.53 0.4768 0.5525 0.2161 0.0544 0.27 244.5 7 0.35 0.4218 0.4727 0.2612 0.0489 0.27 363.0 8 0.75 0.4759 0.4847 0.2139 0.0531 0.28 280.5 9 0.62 0.4636 0.5389 0.2283 0.0533 0.26 256.5 10 0.59 0.4659 0.5548 0.2295 0.0559 0.26 241.5 11 0.90 0.6334 0.5943 0.1127 0.0763 0.23 130.0 12 0.89 0.6366 0.6138 0.1000 0.0753 0.24 127.5 13 0.90 0.6267 0.6736 0.1075 0.0758 0.25 120.0

a Lens matrix= PEGMA:EBPDMA 1:4 mass composition. Samples initially irradiated at 350-400 nm for 1000 seconds, then decolouration monitored at max of the coloured form (pre-determined by wavelength scan of coloured form) at 20 °C in the dark for 4800 seconds; b Measured absorbance intensity at onset of thermal decolouration period; c Time taken for the initial absorbance value, A0, to decay to half.

The partitioning of PEG tails around attached dye moieties provides an overall insulation and encapsulation effect in the host matrix.13 This effect is not as strong as that provided with PDMS (polydimethylsiloxane) tailing, which allows kinetics in the lens matrix to more closely approach that of solution: the T1/2 value for PEG conjugate 3 is 88.5 s vs. 63 s for an equivalent length PDMS-dye conjugate.12 Furthermore, only a very small effect is seen from decreasing EG repeat units from n = 18 for 1 (T1/2 is 82.5 s) to n = 14 and n = 11 for 2 and 3 respectively (T1/2 is 88.5 s). This is likely due to the greater compatibility and solubility of PEG with the host matrix which also contains a substantial EG component. Nonetheless, like the PDMS conjugates tested in a previous study, the PEG conjugates did display a diminished contribution term, A2 for the slower kinetic component of the fade, k2, as compared to control sample 13 (0.06 vs. 0.11). A diminishing A2 term in turn implies that kinetics are more similar to the purely biexponential decays displayed by a naphthopyran dye in solution and therefore is

186 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______indicative of a more homogenous and less disperse local environment created for dye molecules within the matrix. Lyubimov et al.25 studied the behaviour of spiroyran photochromics in network polymers. His work claimed that the inhomogenous nature of the network structure has a more pronounced effect on photochromic kinetics when the dye is chemically bound to it. This is because the dye molecules end up in places that greatly differ in terms of chain packing density and free volume. When the molecules have no polymerizable group and are not able to connect to the network structure they end up migrating into similar micro-cavities and domains and therefore end up in an overall less dispersive environment. Their photochromic kinetics therefore give a lower value of A2, compared to polymerizable spiropyrans. This is also exemplified here with higher A2 values displayed by dyes bound to the lens matrix: monomers 4-10 gave A2 values between 0.13 and 0.26 compared to values < 0.11 for non-bound dyes.

400

300

200

(s) decoloration decay 100 1/2 T

0 12313412115106987 Photochromic Sample

Figure 5. Comparison of T1/2 values of decolouration decay of lens samples tested.

In order to compare decolouration behaviour collectively, the T1/2 values for each sample, from lowest (fastest) to highest (slowest), was plotted as Figure 5. Based on decolouration speed, the data could be divided into three portions: The fastest lot contained matrix-unbound PEG-dye conjugates 1 - 3, an intermediate group contained all the control dyes 11 - 13, followed by the slowest group which was only represented by matrix-bound dyes. Photochromic decolouration occurs through a series of bond rotations (double and single) followed by ring closure. Overall the process requires substantial intramolecular

187 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

movement as both sections of the molecule need to be relocated with respect to one another (as shown in Figure 1). The lens matrix is a rigid three-dimensional network structure in which polymer chains are inter-connected and have low segmental mobility at ambient temperature. It is expected that the chemical linking of a dye to this structure would greatly restrict their ability to move during the photochromic transition since the full process requires some cooperation from local chain segments of the network structure. Therefore, it is not unexpected that the slowest kinetics (highest T1/2 values) were displayed by monomer structures that became linked to the network structure during curing (i.e. 6 - 10). Interestingly monomers, 4 and 5, which contained EG spacer/s between the dye and the tethering point displayed faster decolouration kinetics compared to all other monomers, giving T1/2 values comparable to those of unbound controls. It would appear that the presence of a lubricating, flexible tail separating the tethering point and the dye molecule allows it to have increased mobility for ring closure. This may be a result of lower packing density and increased segmental mobility of chains in the vicinity of the dye in the final network structure. Monomer 4 which contained 10 EG repeat units displayed only moderately faster kinetics compared to 5 which already contained 1 EG unit (T1/2 121.5 s for 4 vs. 132 s for 5). When comparing the fade kinetics of monomers 5 and 10 however, it is evident that the most significant impact on kinetics is made by the spacer itself, in this case EG- succinate, which is located close to the dye (T1/2 132 s for 5 vs. 241.5 s for 10). Therefore, the location of the dye with respect to the network tethering point is an important criterion for affecting kinetics and confirms again the extreme sensitivity of the dye to its local environment. The closer the dye is to the tethering point, the larger the effect. Photochromic dyes having only one polymerizable group can be considered side pendants in the network structure. When the photochromic dye is linked to the network by both parts of its molecular structure (as in 6 and 7), this could present a very significant hindrance to isomerization and ring closure. Not surprisingly, bismethacrylate 7 displayed the slowest kinetics of the entire lot (with T1/2 363 s). Lyubimov25 also investigated a network system incorporating a spiropyran attached by two polymerizable groups. The system also displayed biexponential kinetics, however, one rate constant was notably fast. They reasoned this was due to less stable and strained open forms being formed as a result of restrictions imposed on movement by bis-tethering. Similarly, there have also been similar reports in literature showing that

188 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______rates of thermal decay of photochromics bonded into glassy matrices which are larger than those observed in solution.26-28 These results do not demonstrate this to be the case, with both rate constants for 7 being particularly low. In comparison to 7, bismethacrylate 6 which contained an extra EG-succinate spacer on the top and bottom of the molecule was significantly faster (T1/2 244.5 s). Again, a vicinal spacer appears to have a marked influence on kinetics. It is interesting, however, that the position of the methacrylate group, whether on the top or the bottom part of the molecule, was also found to have an influence on kinetics. This is exemplified by the difference in kinetics displayed between monomers 8, 9 and 10. Samples 9 and 10, with a methacrylate positioned on the bottom section of the molecule displayed faster kinetics than 8 which had a methacrylate on the top section (T1/2 241.5 s and 256.5 s for 10 and 9 vs. 280.5 s for 8). When referenced back to their corresponding controls (control 12 for comparison to monomer 10 and control 11 for comparison to monomers 8 and 9), monomer 8, with a methacrylate group located on the top section of the molecule, was found to be comparatively slower (2.2 times slower) compared to monomers 9 and 10 which were only 1.9 times slower than their controls. A preference for either dye portion to associate with the aromatic component of the matrix could account for this disparity. However this notion was discounted by a similar trend displayed by the monomers when reacted with a matrix composition consisting entirely of PEG 400 dimethacrylate. In this case monomer 8 also displayed comparatively slower kinetics (Table 3).

Table 3: Photokinetic analysis of decolouration of naphthopyrans in PEGMA lens matrix.a k k Sample A b A 1 A 2 A T (s) c 0 1 (min-1) 2 (min-1) th 1/2 11 (control) 0.99 0.7357 1.1578 0.0147 0.0633 0.24 54 8 1.00 0.6259 1.1773 0.1338 0.3352 0.24 68 9 0.98 0.6445 1.2043 0.1488 0.2247 0.19 60 10 0.99 0.6318 1.3895 0.1599 0.2973 0.21 56 a Matrix consisted of 100% polyethylene glycol (400) dimethacrylate b Samples initially irradiated at 350-400 nm for 1000 seconds, then decolouration monitored at b max of the coloured form at 20 °C in the dark for 4800 seconds Measured absorbance intensity at onset of thermal decolouration period. c Time taken for the initial absorbance value, A0, to decay to half its original value.

189 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

For decolouration to take place, one portion of the molecule needs to be redistributed relative to the other. A number of possible configurations could give rise to the correct activated states for ring closure and linking through the top portion of the molecule may supply less energetically favorable pathways. This could originate from differences in steric bulk, volume and interactions of the two sections of the dye molecule with the matrix environment. This could also account for differences in kinetics. Miyazaki et al.29 studied the crosslinking polymerization characteristics of different dimethacrylates in relation to the chemical structure of monomers. Interestingly they found that the extent of polymerization and crosslinking efficiency increased with the number of functional groups located between the methacrylate groups. So, dimethacrylates consisting of longer aliphatic or flexible chains were thought to be more mobile and polymerize more readily compared to those containing aromatic groups. Presumably then, the top methacrylate functionality in monomer 8, separated from the aromatic group by an EG unit, may be more completely incorporated into the network structure as compared to the bottom-functionalized methacrylates, 9 and 10, in which the reactive methacrylate emerges directly from the naphthol portion of the dye. Overall this could also account for the slower kinetics displayed by 8. This aspect was further investigated in the next chapter. The UV-colouration period involves competitive thermal and photochemical pathways interconverting the isomers which results in complex kinetics. In solution it is known that a slower rate of thermal decolouration can give rise to a higher level of 30 colourabilty, A0. This is because thermal reversion can affect the amount of colourless form available under steady-state irradiation. However, there is also potential for colouration to be diminished due to the difficulty experienced by dye molecules in achieving the necessary conformations for ring opening. Furthermore there may be more opportunity for competing processes to occur that deactivate excited states that lead to coloured isomers. This is particularly important when considering photochromic behaviour within a rigid environment. In fact, as I have discovered in previous work,10 dyes conjugated to more rigid polymer tails (e.g. pMMA) which display slower kinetics can also give rise to diminished colourabilities. This was also the case in this work, where a decrease in the major thermal bleaching constant k1, with respect to that of corresponding controls, was found to be associated with an overall decrease in colourability (Figure 6). Monomer 8 was a standout since its particularly slow

190 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

decolouration kinetics gave rise to a comparatively higher A0 value (A0 = 0.75). This implies that the resulting tethered structure experiences less photochemical losses.

Figure 6. Evolution of k1(compound)/k1(control) with A0 (compound)/A0 (control), showing relationship between rate of decolouration and colourability.

6.3 Conclusion

Various naphthopyran dyes were reacted with a lens matrix composition to become part of the final crosslinked network structure. The behaviour of these photochromic network polymers was investigated. Tethering to the rigid matrix restricts the ability of the dye to move and universally causes a decrease in colouration and decolouration rates, compared to unbound dyes. Tethering to the network structure with two reactive points located on opposite sides of the dye molecule causes a further reduction in switching speed and very low levels of colouration. The fade kinetics displayed by matrix tethered dyes was also found to be more complex indicating that their local environment is less homogenous overall. A PEG spacer separating one tethering point from the dye allowed fade kinetics to approach those of untethered controls. An EG-succinate spacer directly separating the tethering point/s from the dye itself was found to have the largest impact. Longer spacers had less of an effect on the kinetics. The position of the tethering point with respect to the dye, whether attached through the top or bottom section of the molecule, was also found to significantly influence both fade kinetics and colourability.

191 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

6.4 Experimental Details

Materials. All chemicals (reagents and solvents) used for synthesis were of the highest purity available and used as received unless otherwise stated. All reagents were purchased from Aldrich Chemical Co., unless otherwise stated. All chromatography was performed using silica gel (Kieselgel Merck 60, 0.040 - 0.063 mm) and TLC was performed on Merck Silica 60F254 plates. The synthesis of mono-hydroxyl functionalized naphthopyran, methyl 6-hydroxy-2- 10 (4-methoxyphenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate ; bis-hydroxyl functionalized naphthopyran, methyl 6-hydroxy-2-(4-(2-hydroxyethoxy)phenyl)-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate11; methyl 6-(isobutyryloxy)-2-(4- methoxy-phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (12)10; methyl 6- (methacryloyloxy)-2-(4-methoxy-phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5 carboxylate (10)10; methyl 6-(propionyloxy)-2-(4-methoxy-phenyl)-2-phenyl-2H- naphtho[1,2-b]pyran-5-carboxylate (13)12; methyl 6-(isobutyryloxy)-2-(4-(2- (isobutyryloxy)ethoxy)phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (11)11 have all been described by us in literature.

General Experimental Measurements. 1H (400 MHz) and 13C NMR (100 MHz) spectra were obtained with a Bruker Av400 spectrometer at 25 °C. Spectra were recorded for samples dissolved in deuterated solvent and chemical shifts are reported as parts per million from external tetramethylsilane. Example 1H NMR spectra are displayed in Appendix 4 (pages A16-A17). Positive ion EI mass spectra were run on a ThermoQuest MAT95XL mass spectrometer using ionization energy of 70 eV. Accurate mass measurements were obtained with a resolution of 5000-10000 using PFK as the reference compound.

Photochromic Analysis. Under continuous UV irradiation, the photochromic responses of the samples (cured lenses) were analyzed on a light table composed of a Cary 50 spectrophotometer for measuring the absorbance and a 160 W Oriel xenon lamp as the incident UV light source. A series of two filters (Edmund Optics 320 cut-off and bandpass filter U-340) were used to restrict the output of the lamp to a narrow band (350-400 nm). The samples were maintained at 20 °C and monitored at the maximum absorbance of the coloured form (max) firstly during colouration for a period of 1000 s. Then the thermal decolouration was monitored in the absence of UV irradiation for a further 4800 s. 192 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

Preparation of Photochromic Lens Samples. The naphthopyran dyes were individually dissolved in a standard industrial lens formulation made up of 1:4 weight ratio of poly(ethylene glycol) (400) dimethacrylate and 2,2’-bis((4- methacryloxyethoxy)phenyl)propane (monomer structures given in Figure 1) with 0.4% by mass of AIBN. The samples were then cured at 80 C for 16 hrs in a standard mold to give optically clear test samples of equivalent thickness (~2.4 mm). They were each doped at equivalent concentrations of 1.5 × 10-7 mol dye / gram of lens formulation. This concentration was chosen in order to maintain the absorbance values in a meaningful range for the detector.

Synthesis of COOH terminated PEG (MeO-PEG-COOH, n=17). A solution of polyethylene glycol (750) methyl ether (5 g, 6.67 mmol), succinic anhydride (0.734 g, 7.34 mmol), triethylamine (TEA) (0.734 g, 7.34 mmol) and dimethyl aminopyridine (DMAP) (10 mg, 0.081 mmol) was prepared in dichloromethane (DCM) (25 mL) and stirred under argon at 35 C for 8 hours. The mixture was then diluted with DCM (100 mL) and washed with 2M HCl (2 × 30 mL), followed by brine. The DCM solution was dried with anhydrous anhydrous MgSO4 overnight, filtered and the solvent removed under vacuum to give 5.23 g of clear oil. 1H and 13C NMR showed the material, MeO- PEG-COOH, to be free of starting material and of sufficient purity for subsequent use. The oil was dried under vacuum with gentle heating (40 C) and stored under nitrogen. 1 Mn 860.7 g/mol; H NMR (400 MHz, CDCl3) : 2.62 (s, 4H, OCCH2CH2CO), 3.35 (s,

3H, OCH3), 3.52 - 3.62 (m, 64H, O(CH2CH2), 4.23 (t, 2H, J 4.8 Hz, COOCH2) ppm.

Synthesis of Succinoyl chloride terminated PEG (MeO-PEG-COCl). MeO-PEG- COOH (made as in previous step) (400 mg, 0.465 mmol) was added to dry DCM (10 mL) followed by one drop of dimethylformamide (DMF). The solution was stirred under argon at room temperature for 5 minutes and then oxalyl chloride (177 mg, 118 L, 1.4 mmol) was added in one portion. The solution was then left to stir at room temperature for 1 hour. The solvent and excess reagents were removed under vacuum

193 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

with residual traces of oxalyl chloride removed with the aid of 1,2-dichloroethane (DCE). The acid chloride was used immediately as is.

Synthesis of methyl 6-(polyethylene glycol (750) methyl ether succinoyloxy)-2-(4- methoxy-phenyl)-2-phenyl-2H-naptho[1,2-b]pyran)-5-carboxylate, 1. A solution of MeO-PEG-COCl, synthesized as per previous step (409 mg, 0.465 mmol) in DCM (7 mL) was slowly added to a stirring solution of methyl 6-hydroxy-2-(4-methoxyphenyl)- 2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (185 mg, 0.422 mmol) and TEA (99 mg, 136 L, 0.98 mmol) in DCM (10 mL). The solution was stirred under argon for 1 hour at room temperature. Water was then added (20 mL) and the solution extracted with DCM (3 × 20 mL). The organic layer was dried with anhydrous. MgSO4 and the solvent evaporated under vacuum. The product was isolated as an orange oil after purification by column chromatography (silica gel 60, gradual elution: 1 EtOAc(EtOAc/MeOH)MeOH) (270 mg, 50%). H NMR (400 MHz, CDCl3) :

2.82 (t, 2H, J 6.2 Hz, OCCH2CH2CO), 3.10 (t, 2H, J 6.2 Hz, OCCH2CH2CO), 3.38 (s,

3H, CH2OCH3), 3.53 - 3.56 (m, 2H, O(CH2CH2)), 3.62 - 3.71 (m, 66.2 H, O(CH2CH2)),

3.76 (s, 3H, ArOCH3), 3.95 (s, 3H, COOCH3), 4.27 - 4.29 (m, 2H, COOCH2), 6.17 (d, J 10.08 Hz, 1H, pyran-H), 6.83 (apparent d, J 8.50 Hz, 2H, ArH), 6.93 (d, J 10.08 Hz, 1H, pyran-H), 7.23 - 7.27 (m, 1H, ArH), 7.30 - 7.34 (m, 2H, ArH), 7.38 (apparent doublet, J 8.42 Hz, 2H, ArH), 7.46 - 7.57 (m, 4H, ArH), 7.78 (d, J 8.07 Hz, 1H, ArH), 13 8.34 (d, J 8.07 Hz, 1H, ArH) ppm. Mn 1,340 g/mol. C NMR (100 MHz, CDCl3) : 28.9, 28.9, 52.5, 55.2, 59.0, 63.7, 69.0, 70.5, 71.9, 82.8, 113.1, 113.5, 119.1, 121.1, 122.4, 122.5, 126.5, 126.7, 127.2, 127.5, 127.7, 127.7, 128.16, 128.2, 128.4 , 136.6, 139.5, 144.8, 146.3, 159.0, 165.9, 170.9, 172.1 ppm.

Synthesis of methyl 6-(polyethylene glycol (550) methyl ether succinoyloxy)-2-(4- methoxy-phenyl)-2-phenyl-2H-naptho[1,2-b]pyran)-5-carboxylates, 2 and 3. The title compounds were synthesized from of polyethylene glycol (550) methyl ether using the same procedure as described above for 1. Fractionation of the product during column chromatography allowed 2 and 3 to be collected separately with Mn 1,190 g/mol and 1,050 g/mol respectively. The corresponding NMRs were consistent with that of 1 with lower integral values for multiplet at 3.62 - 3.71 ppm due to lower number of ethylene glycol units.

194 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

Synthesis of naphthopyran polyethylene glycol (526) methacrylate succinate, 4. The title compound was synthesized from mono-hydroxylated naphthopyran and methacrylate-PEG-COCl, using the same procedure as described above for 1 - 3. 1H

NMR (200 MHz, CDCl3) : 1.95 (s, 3H, CH3C=CH2), 2.83 (t, 2H, J 6.2 Hz,

OCCH2CH2CO), 3.02 (t, 2H, J 6.2 Hz, OCCH2CH2CO), 3.63 - 3.71 (m, 38H,

O(CH2CH2), 3.76 (s, 3H, OCH3), 3.96 (s, 3H, COOCH3), 4.27 - 4.28 (m, 4H,

OCOCH2CH2), 5.58 (s, 1H, C=CH), 6.14 (br s, 1H, C=CH), 6.17 (d, J 10.1 Hz, 1H, pyran-H), 6.83 (apparent d, J 8.50 Hz, 2H, ArH), 6.95 (d, J 10.1 Hz, 1H, pyran-H), 7.23 - 7.57 (m, 9H, ArH), 7.78 (d, J 8.07 Hz, 1H, ArH), 8.34 (d, J 8.07 Hz, 1H, ArH) ppm. Mn 1,070 g/mol.

Synthesis of methacrylate-EG-succinoyl chloride. Mono-2-(methacryloyloxy)ethyl succinate (Methacrylate-EG-Succinate) (529 mg, 2.30 mmol) was added to dry DCM (30 mL) followed by one drop of dimethylformamide (DMF). The solution was stirred under argon at room temperature for 5 minutes and then oxalyl chloride (876 mg, 592 L, 6.90 mmol) was added in one portion. The solution was then left to stir at room temperature for 1 hour. The solvent and excess reagents were removed under vacuum with residual traces of oxalyl chloride removed with the aid of 1,2-dichloroethane (DCE). The acid chloride product was used immediately as is.

Synthesis of methyl 6-(4-(2-(methacryloyloxy)ethoxy)-4-oxobutanoyloxy)-2-(4- methoxyphenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate, 5. A solution of methacrylate-EG-succinoyl chloride, synthesized as per previous step (572 mg, 2.30 mmol) in DCM (10 mL) was slowly added to a stirring solution of methyl 6-hydroxy-2- (4-methoxyphenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (1.50 g, 2.30 mmol) and TEA (512 mg, 705 L, 5.06 mmol) in DCM (30 mL). The solution was stirred under argon for 1 hour at room temperature. Water was then added (50 mL) and

195 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

the solution extracted with DCM (3 × 50mL). The organic layer was dried with anhyd.

MgSO4 and the solvent removed under vacuum. Purification by column chromatography (silica gel 60, diethyl ether/toluene (1:9)) gave the product as red 1 coloured sticky solid (1.25 g, 83%). H NMR (400 MHz, CDCl3) : 1.89 (s, 3H,

=CCH3), 2.81 (m, 2H, CH2), 3.02 (m, 2H, CH2), 3.76 (s, 3H, ArOCH3), 3.95 (s, 3H,

COOCH3), 4.37 (br s, 4H, 2 × CH2), 5.50 (m, 1H, 1H, =CH), 6.08 (m, 1H, 1H, =CH), 6.17 (d, J 10.0 Hz, 1H, pyran-H), 6.83 (apparent d, J 8.8 Hz, 2H, ArH), 6.93 (d, 1H, J 10.0 Hz, pyran-H), 7.20 - 7.60 (m, 9H, ArH), 7.75 - 7.80 (m, 1H, ArH), ), 7.30 - 7.37 13 (m, 1H, ArH) ppm. C NMR (100 MHz, CDCl3) : 18.3, 28.9, 29.0, 52.7, 55.4, 62.4, 62.7, 83.0, 113.2, 113.7, 119.2, 121.3, 122.5, 122.5, 126.2, 126.6, 126.9, 127.4, 127.7, 127.9, 127.9, 128.3, 128.4, 128.5, 135.9, 136.7, 139.7, 145.0, 146.4, 159.2, 166.0, 167.2, 171.0, 172.1 ppm.

Synthesis of methyl 6-(4-(2-(methacryloyloxy)ethoxy)-4-oxobutanoyloxy)-2-(4-(2- (methacryloyloxy)ethoxy-4-oxobutanoyloxy)ethoxy-phenyl)-2-phenyl-2H-naphth - o[1,2-b]pyran-5-carboxylate), 6. A solution of methacrylate-EG-succinoyl chloride, synthesized as per previous step (405 mg, 1.66 mmol) in DCM (10 mL) was slowly added to a stirring solution of methyl 6-hydroxy-2-(4-(2-hydroxyethoxy)phenyl)-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (0.380 g, 0.811 mmol) and TEA (369 mg, 509 L, 3.65 mmol) in DCM (15 mL). The solution was stirred under argon for 1 hour at room temperature. Water was then added (30 mL) and the solution extracted with DCM (3 × 30mL). The combined organic extracts were dried with anhydrous

MgSO4 and the solvent removed under vacuum. Purification by column chromatography (silica gel 60, MeOH/EtOAc/Tol (5/20/75)) gave the product as red 1 coloured sticky solid (0.41 g, 57%). H NMR (200 MHz, CDCl3) : 1.90 (m, 3H,

=CCH3), 1.93 (s, 3H, =CCH3), 2.64 (s, 4H, 2 × CH2 ), 2.78 - 2.85 (m, 2H, CH2), 2.99 -

3.05 (m, 2H, CH2), 3.95 (s, 3H, COOCH3), 4.09 - 4.14 (m, 2H, CH2), 4.32 (s, 4H, 2 ×

CH2 ), 4.35 - 4.43 (m, 6H, 3 × CH2), 5.51 (p, 1H, J 1.53 Hz, =CH), 5.57 (p, 1H, J 1.53 Hz, =CH), 6.06 - 6.09 (m, 1H, =CH), 6.10 - 6.13 (m, 1H, =CH), 6.16 (d, J 10.0 Hz, 1H, pyran-H), 6.83 (apparent d, J 8.8 Hz, 2H, ArH), 6.93 (d, 1H, J 10.0 Hz, pyran-H), 7.25 - 7.60 (m, 9H, ArH), 7.76 - 7.80 (m, 1H, ArH), 8.32 - 8.36 (m, 1H, ArH) ppm. 13C NMR

(50 MHz, CDCl3) : 18.4, 18.4, 28.9, 29.0, 29.0, 29.0, 52.7, 62.4, 62.4, 62.5, 62.7, 63.2, 65.9, 82.9, 113.3, 114.3, 119.2, 121.4, 122.5, 122.6, 126.2, 126.3, 126.6, 126.9, 127.4,

196 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

127.7, 127.9, 128.0, 128.3, 128.3, 128.6, 135.9, 136.0, 137.3, 139.7, 144.9, 146.4, 158.1, 165.9, 167.2, 167.2, 170.9, 172.1, 172.1, 172.2 ppm.

Synthesis of methyl 6-(methacryloyloxy)-2-(4-(2-(methacryloyloxy)ethoxy) phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate, 7. Methacryloyl chloride (105 mg, 98L 1.12 mmol was slowly added to a stirring solution of methyl 6-hydroxy- 2-(4-(2-hydroxyethoxy)phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (0.250 g, 0.534 mmol) and TEA (136 mg, 187 L, 1.34 mmol) in DCM (15 mL). The solution was stirred under argon for 1 hour at room temperature. Water was then added (20 mL) and the solution extracted with DCM (3 × 20mL). The combined organic extracts were dried with anhyd. MgSO4 and the solvent removed under vacuum. Purification by column chromatography (silica gel 60, EtOAc/Hexane, 20/80) gave the product as a 1 pink crunchy solid (230 mg, 70%). H NMR (400 MHz, CDCl3) : 1.91 (s, 3H, =CCH3),

2.12 (s, 3H, =CCH3), 3.88 (s, 3H, COOCH3), 4.18 (t, 2H, J 4.76 Hz, CH2CH2OAr), 4.45

(t, 2H, J 4.76 Hz, CH2CH2OAr), 5.54 (m, 1H, =CH), 5.83 (br s, 1H, =CH), 6.09 (br s, 1H, =CH), 6.17 (d, J 10.0 Hz, 1H, pyran-H), 6.44 (br s, 1H, =CH), 6.85 (apparent d, J 8.8 Hz, 2H, ArH), 6.97 (d, 1H, J 10.0 Hz, pyran-H), 7.24 - 7.28 (m, 2H, ArH), 7.31 - 7.34 (m, 2H, ArH), 7.41 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.47 - 7.58 (m, 3H, ArH), 7.72 (d, J 8.6 Hz, 1H, ArH), 8.35 (d, J 8.6 Hz, 1H, ArH) ppm. 13C NMR (100

MHz, d6-acetone) : 18.3, 18.5, 52.8, 63.9, 66.8, 83.6, 114.4, 115.2, 120.8, 121.9, 123.1, 123.4, 125.9, 127.1, 127.4, 128.1, 128.3, 128.4, 128.8, 128.9, 129.0, 129.1, 130.1, 136.5, 137.2, 137.8, 140.5, 145.9, 146.8, 159.3, 166.0, 166.2, 167.4 ppm.

197 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

Synthesis of methyl 6-(isobutyryloxy)-2-(4-(2-(methacryloyloxy)ethoxy)phenyl)-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate, 8. The synthesis of the title compound was carried out in two steps. Methacryloyl chloride (162 mg, 151 L, 1.55 mmol) was slowly added to a stirring solution of methyl 6-hydroxy-2-(4-(2- hydroxyethoxy)phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (0.725 mg, 1.55 mmol) and TEA (188 mg, 260 L, 1.86 mmol) in DCM (15 mL). The solution was stirred under argon for 3 hours at room temperature. This generated a mixture of 4 products (as shown in scheme above) which gave 4 separate spots on TLC (MeOH/EtOAc/Tol (5/20/75)) consisting of, from top (fastest) spot to bottom (slowest) spot: mono-hydroxylated naphthopyran with methacrylate functionality on top (top orange spot); bis-methacrylate functionalized dye 7 (pink spot); unreacted starting material (orange spot) and mono-hydroxylated naphthopyran with methacrylate functionality on the bottom (pink spot, slowest). These were separated by column chromatography (silica gel 60), firstly with EtOAc/Tol (20/80) to collect the first two

198 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______products separately and then MeOH/EtOAc/Tol (5/20/75) to collect the two other slower running products separately. The retrieved unreacted starting material could then be used for synthesis of naphthopyrans 6, 7 and 11 using the above-described procedures. The mono-hydroxylated naphthopyran with methacrylate functionality on top was 1 collected as an orange solid (220 mg). H NMR (400 MHz, d6-acetone) : 1.86 (s, 3H,

CH3), 4.05 (s, 3H, COOCH3), 4.23 (t, 2H, J 4.50 Hz, CH2CH2OAr), 4.43 (t, 2H, J 4.50

Hz, CH2CH2OAr), 5.57 (br s, 1H, =CH), 6.01 (br s, 1H, =CH), 6.38 (d, J 10.0 Hz, 1H, pyran-H), 6.89 (apparent d, J 8.8 Hz, 2H, ArH), 7.21 - 7.26 (m, 1H, ArH), 7.31 - 7.35 (m, 2H, ArH), 7.47 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.52 (d, J 10.0 Hz, 1H, pyran-H), 7.56 - 7.63 (m, 3H, ArH), 7.75 - 7.79 (m, 1H, ArH), 8.32 (d, J 8.4 Hz, 1H, 13 ArH), 8.42 (d, J 8.4 Hz, 1H, ArH), 12.17 (s, 1H, ArOH) ppm. C NMR (100 MHz, (d6- acetone) : 18.3, 53.1, 63.9, 66.8, 82.9, 103.2, 114.5, 115.0, 122.8, 124.5, 124.7, 125.9, 126.0, 127.3, 127.6, 128.2, 128.7, 128.9, 129.0, 129.4, 130.8, 137.2, 138.0, 141.9, 146.1, 157.0, 159.1, 167.4, 172.8 ppm. The product (0.200 g, 0.373 mmol) was dissolved into DCM (7 mL) along with TEA (68 mg, 94 L, 0.672 mmol). To the mixture, stirring at room temperature under argon, was added dropwise, isobutyryl chloride (48 mg, 47L, 0.45 mmol). Water was then added (10 mL) and the solution extracted with DCM (3 × 10mL). The combined organic extracts were dried with anhyd. MgSO4 and the solvent removed under vacuum. Purification by column chromatography (silica gel 60, EtOAc/Hexane, 20/80) gave the 1 product as a pink solid (200 mg, 90%). H NMR (400 MHz, d6-acetone) : 1.35 (s, 3H,

CH3), 1.37 (s, 3H, CH3), 1.86 (s, 3H, =CHCH3), 3.0 (sept, 1H, J 6.95 Hz, CH(CH3)2),

3.92 (s, 3H, COOCH3), 4.23 (t, 2H, J 4.57 Hz, CH2CH2OAr), 4.44 (t, 2H, J 4.57 Hz,

CH2CH2OAr), 5.57 - 5.58 (m, 1H, =CH), 6.02 (br s, 1H, =CH), 6.47 (d, J 10.0 Hz, 1H, pyran-H), 6.93 (apparent d, J 8.8 Hz, 2H, ArH), 7.00 (d, 1H, J 10.0 Hz, pyran-H), 7.26 - 7.29 (m, 1H, ArH), 7.34 - 7.38 (m, 2H, ArH), 7.48 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.56 - 7.63 (m, 3H, ArH), 7.67 - 7.70 (m, 1H, ArH), 7.84 (d, J 8.6 Hz, 1H, ArH), 13 8.45 (d, J 8.6 Hz, 1H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 18.3, 19.3, 34.7, 52.9, 63.9, 66.8, 83.6, 114.2, 115.1, 121.1, 121.8, 123.0, 123.2, 125.9, 127.0, 127.3, 128.3, 128.4, 128.7, 128.8, 129.0, 129.1, 130.0, 137.2, 137.8, 140,0, 145.9, 146.6, 159.3, 166.3, 167.4, 175.4 ppm.

199 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

Synthesis of methyl 6-(methacryloyloxy)-2-(4-(2-(isobutyryloxy)ethoxy)phenyl)-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate, 9. The mono-hydroxylated naphtho- pyran with methacrylate functionality on the bottom was collected from the column as a 1 pure compound (40 mg). H NMR (400 MHz, d6-acetone) : 2.09 (s, 3H, CH3), 3.80 -

3.84 (m, 2H, CH2CH2OH), 3.89 (s, 3H, COOCH3), 3.92 - 3.95 (m, 1H, OH), 4.01 - 4.08

(m, 2H, CH2CH2OAr), 5.92 (br s, 1H, =CH), 6.39 (br s, 1H, =CH), 6.47 (d, J 10.0 Hz, 1H, pyran-H), 6.90 (apparent d, J 8.8 Hz, 2H, ArH), 7.00 (d, 1H, J 10.0 Hz, pyran-H), 7.26 - 7.29 (m, 1H, ArH), 7.34 - 7.38 (m, 2H, ArH), 7.49 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.56 - 7.63 (m, 3H, ArH), 7.67 - 7.71 (m, 1H, ArH), 7.81 (d, J 8.6 Hz, 1H, 13 ArH), 8.46 (d, J 8.6 Hz, 1H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 18.5, 52.8, 61.2, 70.5, 83.6, 114.4, 115.0, 120.8, 121.80, 123.0, 123.4, 127.0, 127.3, 128.1, 128.2, 128.4, 128.7, 128.9, 128.9, 129.1, 130.1, 136.4, 137.3, 140.4, 145.9, 146.7, 159.6, 166.0, 166.2 ppm. The synthesis of the title compound 9 was carried out analogously to 8, using isobutyryl chloride. Purification by column chromatography (silica gel 60, EtOAc/Hexane, 20/80) 1 gave the product as a pink solid (30 mg, 67%). H NMR (400 MHz, d6-acetone) : 1.06

(s, 3H, CH3), 1.08 (s, 3H, CH3), 2.08 (s, 3H, =CHCH3), 2.51 (sept, 1H, J 6.95 Hz,

CH(CH3)2), 3.86 (s, 3H, COOCH3), 4.19 (t, 2H, J 4.57 Hz, CH2CH2OAr), 4.36 (t, 2H, J

4.57 Hz, CH2CH2OAr), 5.92 - 5.93 (m, 1H, =CH), 6.39 (br s, 1H, =CH), 6.48 (d, J 10.0 Hz, 1H, pyran-H), 6.92 (apparent d, J 8.8 Hz, 2H, ArH), 7.00 (d, 1H, J 10.0 Hz, pyran- H), 7.25 - 7.29 (m, 1H, ArH), 7.34 - 7.38 (m, 2H, ArH), 7.48 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.53 - 7.63 (m, 3H, ArH), 7.67 - 7.71 (m, 1H, ArH), 7.81 (d, J 8.6 Hz, 13 1H, ArH), 8.45 (d, J 8.6 Hz, 1H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 18.4, 19.1, 34.4, 52.8, 63.3, 66.8, 83.5, 114.3, 115.1, 120.7, 121.8, 123.0, 123.3, 127.0, 127.3, 128.2, 128.2, 128.4, 128.8, 128.9, 129.0, 129.1, 130.0, 136.3, 137.7, 140,4, 145.7, 146.7, 159.2, 166.1, 166.2, 177.1 ppm.

6.5 References

(1). Dürr, H., General Introduction. In Photochromism: Molecules and Systems. 1st ed.; Elsevier Science Publishing House: Amsterdam, 1990; Vol. 40. (2). Bouas-Laurent, H.; Durr, H. Pure Appl. Chem. 2001, 73, 639-665. (3). Corns, S. N.; Partington, S. M.; Towns, A. D. Colour. Technol. 2009, 125, 249- 261. (4). Ercole, F.; Davis, T. P.; Evans, R. A. Polym. Chem. 2010, 1, 37-54.

200 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

(5). Berkovic, G.; Krongauz, V.; Weiss, V. Chem. Rev. 2000, 100, 1741-1753. (6). Feringa, B. L.; van Delden, R. A.; Koumura, N.; Geertsema, E. M. Chem. Rev. 2000, 100, 1789-1816. (7). Kawata, S.; Kawata, Y. Chem. Rev. 2000, 100, 1777-1788. (8). Yokoyama, Y. Chem. Rev. 2000, 100, 1717-1739. (9). Pardo, R.; Zayat, M.; Levy, D. C. R. Chimie 2010, 13, 212-226. (10). Ercole, F.; Davis, T. P.; Evans, R. A. Macromolecules 2009, 42, 1500-1511. (11). Ercole, F.; Malic, N.; Harrisson, S.; Davis, T. P.; Evans, R. A. Macromolecules 2010, 43, 249-261. (12). Ercole, F.; Malic, N.; Davis, T. P.; Evans, R. A. J. Mater. Chem. 2009, 19, 5612- 5623. (13). Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Davis, T. P.; Such, G. K.; Yee, L. H.; Ball, G. E.; Lewis, D. A. Nat. Mater. 2005, 4, 249-253. (14). Evans, R. A.; Such, G. K. Aust. J. Chem. 2005, 58, 825-830. (15). Evans, R. A.; Such, G. K.; Malic, N.; Davis, T. P.; Lewis, D. A.; Campbell, J. A. Photochromic Compounds Comprising Polymeric Substituents and Methods for Preparation and Use Thereof. WO2006024099, 2006. (16). Sriprom, W.; Néel, M.; Gabbutt, C. D.; Heron, M.; Perrier, S. J. Mater. Chem. 2007, 17, 1885-1893; Sriprom, W; Neto, C; Perrier, S, Soft Mat. 2010, 6, 909-914. (17). Henry, D.; Lecrivain, C.; Lecnvain, C. Radically polymerizable composition. WO200206364-A, 2002. (18). Evans, R. A.; Skidmore, M. A.; Lewis, D. A. Polymerizable composition for use in forming a photochromic article, comprises photochromic dye monomer comprising photochromic moiety and oligomer having reactive with monomer component during curing. WO2005105874-A1 (19). Malic, N.; Campbell J. A.; Ali A. S.; Francis, J .L.; Evans R. A. J. Pol. Sci. A. 2011, 49, 2, 476-486. (20). Biteau, J.; Chaput, F.; Boilot, J. P. J Phys Chem 1996, 100, 9024-9031. (21). Delbaere, S.; Luccioni-Houze, B.; Bochu, C.; Teral, Y.; Campredon, M.; Vermeersch, G. J. Chem. Soc., Perkin Trans. 2 1998, 1153-1157. (22). Zayat, M.; Levy, D. J. Mater. Chem. 2003, 13, 727-730. (23). Delbaere, S.; Micheau, J. C.; Vermeersch, G. J. Org. Chem. 2003, 68, 8968-8973. (24). Ottavi, G.; Favaro, G.; Malatesta, V. J. Photochem. Photobiol., A 1998, 115, 123- 128.

201 Chapter 6. Photochromic Behaviour within Highly Crosslinked Networks. ______

(25). Lyubimov, A. V.; Zaichenko, N. L.; Marevtsev, V. S. J. Photochem. Photobiol., A 1999, 120, 55-62. (26). Munakata, Y.; Tsutsui, T.; Saito, S. Polymer J. 1990, 22, 843-848. (27). Paik, C. S.; Morawetz, H. Macromolecules 1972, 5, 171-177. (28). Eisenbach, C. D. Macromol. Chem. Phys. 1978, 179, 2489-2506. (29). Miyazaki, K.; Horibe, T. J. Biomed. Mater. Res. 1988, 22, 1011-1022. (30). Favaro, G.; Malatesta, V.; Mazzucato, U.; Ottavi, G.; Romani, A. J. Photochem. Photobiol., A 1995, 87, 235-241.

202 7 Photochromic Behaviour within Polymer Matrices Part 2: Hyperbranched Polymers

7.1 Introduction

The lens matrix has a three-dimensional network structure in which all chains are interconnected by many covalent crosslinks and could be considered an extreme example of a branched polymer. 1 In this case a single and insoluble macroscopic entity is formed in the bulk using a polymerizable composition consisting entirely of bifunctional monomers. An insoluble gel network can also be formed in a free-radical polymerization mixture when even a smallest amount of bifunctional monomer (crosslinker) is present since this can provide enough interchain branch points.2 In very dilute solution (<<10% monomer), the gel point is normally reached at substantially less than 20% conversion of monomer to polymer.3 Sherrington and coworkers developed an approach for producing highly branched, crosslinked, yet soluble polymer structures, commonly referred to as hyperbranched polymers,4 via the free radical polymerization of multifunctional monomers (Figure 1).5 In this system the presence of a chain transfer agent allows the molecular weight of the primary chains to be substantially reduced to suppress gelation even at high conversion. Furthermore, the number of branching points per primary chain can be controlled by balancing the level of crosslinker (brancher) employed with an appropriate level of chain transfer agent. This method has become known as the ‘Strathclyde route’, as it was developed at the University of Strathclyde in the UK. Since their initial work, others have explored the use of alternative controlled radical polymerization techniques such as ATRP as a way to produce hyperbranched polymer structures.6

Figure 1. Synthesis of hyperbranched polymers using multifunctional monomers and chain transfer agent (CTA). Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

For example, Perrier et al. initially investigated the use of reversible addition fragmentation chain transfer (RAFT) polymerization to prepare highly branched poly(methyl methacrylate), p(MMA), using ethylene glycol dimethacrylate (EGDMA) as the crosslinking, branching agent (CLA).7,8 They were able to produce hyperbranched and soluble p(MMA) in one pot, by keeping the ratio of RAFT agent (RA) to branching agent < 2. Since then, the approach of using RAFT to synthesize branched acrylic copolymers has been studied by others.9-11 Interest in hyperbranched macromolecules has increased because it offers several unique properties compared to linear analogues, including low solution and melt viscosities, improved , tunable solution behaviour and the presence of large numbers of functional end groups. Their dendrimer-like morphology lends well to nanotechnology applications based on the confinement of functional groups and the ability to form pores and cavities within their structures. Although they have less perfect structures and broader polydispersities, hyperbranched polymers are also far easier to prepare.12 They have received industrial attention for many applications such as reactive components in coating and resin formulations.13 The use of such highly branched vinyl polymers as photochromic media has only been explored briefly in literature with respect to spiropyrans and this approach could offer some interesting possibilities for controlling photochromic behavior, as well as probing the nature of the polymeric media.14,15 This work was an initial exploration into the behaviour of photochromic molecules when cross-reacted within highly branched polymer matrices. In these structures MMA and MA were copolymerized with a combination of ethylene glycol and photochromic crosslinkers. The results of Chapter 6, in which some of the monomers were reacted into the network structure of the lens matrix, as well as linear polymers incorporating pendant photochromic units, all served as comparisons to the hyperbranched structures.

204 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

Figure 2. Structures and shortened names of monomers, crosslinking agent (CLA) and RAFT Agent (RA) used to synthesize highly branched and linear polymers.

7.2 Results and Discussion

Unlike a dendrimer, a hyperbranched polymer has an irregular structure with branches distributed randomly throughout. This makes its structure more complicated and difficult to describe. Controlled radical polymerization techniques such as RAFT have been applied using the Strathclyde method with a view to understanding the characteristics of the branching process. Typically, experimental data, such as that of Armes et al 9 show that the molecular weight of the branched polymer begins to grow very rapidly at approximately 50% conversion. This rapid growth in molecular weight is thought to be due to the branching reactions taking place. Since most of these Strathclyde systems show that the molecular weight follows the linear theoretical

205 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______prediction up until about 50% conversion, one would argue that branching is minimal during the early phases of the reaction, compared to the later phases. At lower conversions there is a small probability of branching occurring because the concentration of linear monomer is high compared to the concentration of pendant double bonds. In this early phase of the reaction, the branching monomer/s must also be incorporated into the chain, to give a polymer chain with a pendant double bond. At higher conversions branching is more likely, due to the larger number of pendant double bonds and a lower concentration of linear monomer.10 Armes also showed that the branching copolymerization is significantly slower than the linear homopolymerization and both the final copolymer molecular weight and polydispersity increase with higher levels of branching comonomer. He reasoned that these polymers could also contain many 'loops' due to cyclisation, instead of inter-chain connections, and this was likely to be the case for bulkier and less flexible crosslinkers. Konkolewicz et al outlined a model that gives structural information about a variety of highly branched polymers, called kinetic random branching theory (KRBT).10 The model was used to distinguish between polymers that follow the assumptions of random branching of simple units and polymers that do not. The model was tested on polymers synthesized using the Strathclyde approach under RAFT-mediated control. Of particular interest to this work was the RAFT copolymerization of MMA with EGDMA as the brancher. In the case where the [MMA]:[RA] concentration was 200:1 a good agreement was found between the KRBT and the experimental data, consistent with the polymer being made up of randomly branched units. Here the growth is expected to occur by randomly branching large polymer units to other large polymer units. In the case where the [MMA]:[RA] concentration was 20:1 the KRBT did not hold true. These polymers were able to reach a high conversion using a 20% excess of [CLA] vs. [RA] and were thought to contain more intra-chain loops, giving a structure more like a nanogel. More recent work by Rosselgong, Armes and coworkers investigated the effect of varying the initial monomer concentration on the synthesis of branched p(MMA).11 They found that when the branching copolymerizations were conducted to high conversions using an initial monomer concentration [MMA]0, of 10 % (by mass) and a degree of polymerization (DP) of 50, a relatively high excess of CLA could be tolerated vs. the RA (up to 3× excess), without causing gelation. Their observations suggested that intra-chain cyclisation is prevalent using 10 % [MMA]0. In contrast, inter-chain 206 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

branching between primary chains is thought to be favoured using a 50 % [MMA]0, since this concentration exceeds c*, the coil overlap concentration.16 They found this to be the case regardless of whether ATRP or RAFT was used.

7.2.1 Polymer Synthesis

The structures of reagents used in this study are shown in Figure 2. The polymerization conditions used for polymer synthesis as well as the characteristics of the photochromic polymers are displayed in Table 1 and Table 2 respectively. The conditions used for polymerizations were selected on the basis of published results regarding the synthesis of hyperbranched p(MMA) using RAFT polymerization via a one-pot process.7 In this study the [CLA]: [RA] feed ratio that was used was 1.3 for p(MMA). The CLA was added in a slight excess to make up for possible losses due to incomplete reaction and intra-chain cyclisation. Higher ratios of up to 2 were reported without gelation.7 For branched p(MA), a lower ratio of 1.1 was employed since the first attempt using 1.3 caused gelation at high conversion. To promote a high level of incorporation of crosslinker, and therefore branching in the final polymers, a high conversion was required. The MMA branching polymerizations were carried out for extended times, which is not unusual given that branching polymerizations tend to be slower, but conversions did not exceed 80%. With reference to the previous published work discussed above regarding the structure of the branched polymers, one cannot discount the possibility of substantial intra-chain cyclization taking place. This is more probable for the ethylene glycol crosslinkers that were employed, EGDA and EGDMA, compared to the bulkier photochromic structures, CHRDA and CHRDMA. This at least satisfied the primary goal of exploring the behaviour of photochromic molecules when cross-tethered within branched matrices. However, in the absence of more exhaustive polymerization trials, it remains uncertain whether the polymers have a nanogel structure with a majority of intra-chain loops or a randomly branched structure made up of a majority of inter-chain crosslinks. One could speculate the latter, considering that the polymerizations were conducted using a [monomer]0 of > 60 %, however, more experimental data would be required to come to a structural conclusion. For now, the term ‘highly branched’ would be an appropriate description for the photochromic polymers.

207 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

Table 1. Polymerization conditions used for the synthesis of Hyperbranched (H) and Linear (L) photochromic polymers, p(MMA) and p(MA).a

Monomers Crosslinking CLA RAFT Time Polymer AIBN (total = 100) Agents (CLA) total Agent (RA) (hrs) EGDMA (1.17) H1b,f MMA (100) 1.3 1 0.1 20 CHRDMA (0.13) b,g EGDMA (0.65) H2 MMA (100) CHRDMA (0.65) 1.3 1 0.1 23 b,f MMA (99.87) H3 CHRMA-1 (0.13) PEGDMA (1.3) 1.3 1 0.1 22 c,f MMA (99.87) L1 CHRMA-1 (0.13) - - 1 0.1 22 c,f MMA (99.87) L2 CHRMA-2 (0.13) - - 1 0.1 22 d,g EGDA (0.88) H4 MA (100) CHRDA (0.22) 1.1 1 0.1 7

e,g MA (99.89) - 1 0.1 7 L3 CHRA-1 (0.11) a refer to Figure 1 for structures and abbreviations of reagents. b final ratio of [Monomers] : [CLA] : [RA] : [AIBN] = 100 : 1.3 : 1 : 0.1 c final ratio of [Monomers] : [CLA] : [RA] : [AIBN] = 100 : 0 : 1 : 0.1 d final ratio of [Monomers] : [CLA] : [RA] : [AIBN] = 100 : 1.1 : 1 : 0.1 e final ratio of [Monomers] : [CLA] : [RA] : [AIBN] = 100 : 0 : 1 : 0.1 f photochromic kinetics measured in solution. g photochromic kinetics measured in a film.

Table 2. Characteristics of Hyperbranched (H) and Linear (L) photochromic polymers, p(MMA) and p(MA).

T Polymer Conv. (%)a M b M b PDI g n w (ºC) c H1 p(MMA) 68 13,869 26,323 1.89 120 H2 p(MMA) 78 21,353 63,498 2.97 126 H3 p(MMA) 77 18,528 48,579 2.62 108 L1 p(MMA) 74 8,312 8,810 1.06 116 L2 p(MMA) 74 8,130 8,615 1.06 115 H4 p(MA) 96 24,266 150,288 6.19 20 L3 p(MA) 78 7,858 8,779 1.12 16 a determined by 1H NMR b molecular weight in g/mol determined by GPC with THF as the eluent and calibration using p(MMA) standards for p(MMA) and PS standards for p(MA). c determined by DSC, refer to experimental details.

208 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

Figure 3. Overlaid GPC traces of photochromic hyperbranched polymers: H1-H3 p(MMA) and H4 p(MA). THF eluent and Refractive Index (RI) detection.

The polymers were analyzed using both GPC and 1H NMR. All the linear polymers (L1-L3) had narrow molecular weight distributions as expected from the RAFT process. The GPC traces of the hyperbranched polymers (Fig. 3) were multi-modal and broad, displaying components of higher molecular weight. Taking into consideration the conversions achieved for the polymerizations using an excess of CLA vs. RA, these polymers are expected to contain a high level of branching. Example 1H NMR spectra for polymers H2 and H4 are shown below as Figures 4 and 5 respectively. The rest are displayed in Appendix 5. H2, p(MA), showed undetectable levels of unreacted, pendant monomer units;. H4 p(MMA) had slightly higher levels; followed by H1 in which ~ 20 % of the EG units were left unreacted. Notably this was not the case for H3 which showed complete uptake of the longer PEG crosslinker. As mentioned previously, this may be associated with increased intra-chain cyclisation however this could not be confirmed from its 1H NMR.

209 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

1 Figure 4. H NMR spectrum (in d6-acetone) of hyperbranched poly(methyl methylacrylate), H2, crosslinked with ethylene glycol dimethacrylate (EGDMA) and photochromic dimethacrylate (CHRDMA). Peak assignments: a = (bis)crosslinked ethylene glycol CH2 resonances; b = pendant (mono-reacted) ethylene glycol CH2 resonances; c = pendant vinyl CH2 resonances from (mono-reacted) ethylene glycol; d = OCH3 end group and e = -SCH3 from RAFT end group.

1 Figure 5. H NMR spectrum (in d6-acetone) of hyperbranched poly(methyl acrylate), H4, crosslinked with ethylene glycol diacrylate (EGDA) and photochromic diacrylate (CHRDA). Peak assignments: a = ethylene glycol CH2 resonances; b = terminal CH unit and c = OCH3 end group.

210 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

7.2.2 Photochromic Behaviour

With the exception of H2 p(MMA), structures H1 and H3, displayed poor film forming properties. The cast samples were brittle and produced levels of colour which were too low for measuring and interpreting kinetics. Retrospectively, a higher proportion of photochromic units in the structure would have produced a higher level of colour, as in H2, which was able to form a film that was thick and coloured enough for testing. I therefore decided to explore the kinetics of the p(MMA) structures in solution ( Table 3) since the structures were soluble in toluene.

Table 3. Photokinetic analysis of decolouration displayed by photochromic polymers.a

k k polymer max A b A 1 A 2 A T (s)c (nm) 0 1 (min-1) 2 (min-1) th 1/2 Control 17a d 485 1.42 0.690 1.036 0.240 0.005 0 52 tol. H1 p(MMA) 489 1.29 0.638 0.948 0.285 0.295 0.014 56 tol. H3 p(MMA) 487 1.26 0.556 0.476 0.357 1.554 0.002 54 tol. L1 p(MMA) 487 1.52 0.752 0.542 0.221 2.008 0 54 tol. L2 p(MMA) 487 0.96 0.694 0.590 0.276 2.398 0.002 45 tol. H2 p(MMA) 489 0.46 0.174 0.397 0.390 0.0375 0.388 2020 film H4 p(MA) 495 1.92 0.641 0.135 0.098 0.030 0.273 656 film L3 p(MA) 495 2.06 0.799 0.327 0.229 0.011 0 198 film a Samples initially irradiated at 350-400 nm until steady-state, then decolouration monitored at max of the coloured form at 20 °C in the dark for up to 4000 seconds; (pre-determined by wavelength scan of coloured form); b Measured absorbance intensity at onset of thermal decolouration period; c Time taken for the initial absorbance value, d A0, to decay to half. Control sample reported in Chapter 5, dissolved in toluene 5.0 × 10-5 M. All other polymer samples dissolved as reported in experimental section.

Their measured decolouration responses appeared faster than expected for polymer- bound photochromics, even for solution kinetics. These results were compared to that of the corresponding (propionyl) control dye, 17a, in toluene that was reported earlier in Chapter 5 and to those of linear p(MMA), L1 and L2, which contained pendant photochromics groups. Their T1/2 values were barely unaffected, however, the other kinetic parameters shown in Table 3 appeared markedly altered. When plotted as overlaid decolouration curves the difference in the kinetics of the polymer-bound photochromic samples and the control became even more apparent

211 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

(Figure 6). The control sample was found to produce an isomer population which was more thermally stable and decayed at a slower rate compared to the polymers. This would suggest that for polymer-bound structures a higher level of strain is imposed on a proportion of coloured isomers. This was the case regardless of whether dyes are crosslinked via opposite sides of the molecules (H1 and H3) or pendant from a single point (L1 and L2). This would also suggest that even in solution where polymer chains are considerably free to move, less stable isomers can dominate which decolourize at a faster rate whereas more stable isomer populations are unable to accumulate. In literature this phenomena has been observed only for photochromics tethered into glassy matrices.1,17

Figure 6. Solution kinetics: overlaid and normalised decolouration curves of hyperbranched (H1 and H3) and linear (L1 and L2) p(MMA) vs. the control dye (propionyl derivative, 17a, Ch. 6) in toluene.

The photochromic monomers, CHRMA-1 and CHRMA-2 which were incorporated into the linear p(MMA) structures, L1 and L2, were originally applied in Chapter 6 as structures 10 and 8 respectively. They were investigated with regards to their behaviour when linked to the network structure that comprises the lens matrix: when attached to the network structure via the top part of the molecule, comparatively slower kinetics were obtained (T1/2 280.5 s for 8 compared to T1/2 241.5 s for structure 10). This was an unexpected result considering that structure 8 had an EG spacer separating it from the aromatic portion of the molecule. One of the reasons proposed for this was a difference in the steric bulk and energetics required to relocate the different portions of the molecule with respect to each other and their environment. The results obtained here, however, discount that idea since the opposite behaviour was displayed, with linear

212 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

p(MMA) structure L2, incorporating CHRMA-2, now giving the faster decolouration response in solution compared to linear p(MMA) structure L1. In Chapter 6 I proposed another possible reason for the differences in kinetics with reference to a previous study in the literature.18 In this study the extent of polymerization and crosslinking efficiency of dimethacrylates have been found to increase along with the number of functional groups located between the methacrylate groups. Dimethacrylates consisting of longer aliphatic or flexible chains are thought to be more mobile and polymerize more readily into a crosslinked matrix compared to those containing aromatic groups. In light of this literature precedent I can attribute the comparatively slower decolouration kinetics of structure 8 in the lens matrix, to its higher incorporation into the cured lens structure, originating from an extra spacer separating the methacrylate group from the naphthol part of the molecule, as compared to structures 9 and 10. In this study, the linear polymers, L1 and L2, were purified before testing and therefore incorporated CHRMA-1 and CHRMA-2 fully into their structures. This is in comparison to the lens matrix which could contain some unreacted monomer units as part of the structure. The slightly faster kinetics displayed by the linear structure L2 is therefore likely to be the result of the EG spacer, providing the molecule with more freedom to move away from the restraints of the polymer backbone.

Figure 7. Overlaid and normalised decolouration curves of CHRDMA crosslinked into hyperbranched p(MMA) (H2, film) vs. in the lens matrix, as reported in Chapter 6 as structure 7).

213 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

In comparison to the other p(MMA) samples, I found that photochromic polymers comprised of p(MA) formed far superior films for analysis. The hyperbranched p(MMA) sample, H2, which incorporated a higher concentration of photochromic crosslinking units than the other p(MMA) structures, was also able to form an adequate film for testing. This latter material contains CHRDMA crosslinked into the polymer structure, which was also explored in Chapter 6 when reacted in the lens material (as structure 7). The behaviour of the two bulk media were therefore compared and displayed in Figure 7: one containing the monomer crosslinked into a network (lens) and the other (H2) cross-tethered into a hyperbranched polymer structure. Whilst the bulk material of H2 is held together by fewer junctions than the network structure, it displayed the slower kinetics. An important aspect to consider is that the network lens structure is also composed of a substantial proportion of PEG chains with a long and flexible backbone separating the junctions. This creates a more porous matrix with a distribution of cavities. The soft, elastic nature of the PEG crosslinkers in the network may provide a more open environment for the anchored photochromic units to move, even when attached by both sides of the molecule. By comparison, the hyperbranched structure, H2, is composed of shorter crosslinking units holding the polymer chains in closer proximity. This results in a largely denser structure, which may be overall more restrictive for a bis-anchored photochromic. In a sense, this highlights the importance of free volume, as well as Tg and rigidity, to influence photochromic switching. All these aspects are affected by the structure of the polymer host.

Figure 8. Overlaid and normalised decolouration curves of hyperbranched (H4) and linear (L3) p(MA) films vs. the control dye (propionyl derivative, 17a, Ch. 6) in toluene.

214 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

Hyperbranched p(MA), H4, containing the crosslinked photochromic, CHRDA, displayed faster kinetics compared to p(MMA), H2. This is expected due to higher mobility of p(MA) chains at ambient temperature. Interestingly, its kinetics were also slower than that displayed by CHRDMA crosslinked as part of the lens network (plotted in Figure 7 above). This would also suggest a fairly dense structure for the p(MA) hyperbranched system. Faster again was the linear p(MA) structure, L3, which contains (single) pendant photochromic units (Figure 8). The film produced long-lived colour and isomeric populations that were similar to those displayed by 17a in toluene. This is in contrast to the unusual kinetics displayed by the hyperbranched and linear p(MMA) samples mentioned previously which appeared to produce more strained and less stable isomers in solution.

7.3 Conclusion

This work has introduced some interesting aspects regarding the behaviour of photochromic molecules when cross-tethered within hyperbranched polymer matrices, namely those based on p(MMA) and p(MA). The slower kinetics displayed by the hyperbranched films p(MMA) H2 and p(MA) H4, incorporating bis-tethered photochromic units, as compared to the kinetics the kinetics displayed in the network structure of the lens, indicate that the length of the crosslinking agents are important. The longer and more flexible units in the lens matrix may provide a less dense environment for switching. One hyperbranched system that was not tested as a film was that of hyperbranched p(MA), crosslinked with long PEG spacers and incorporating pendant photochromic groups attached to the polymer backbone from a single point. This could also be compared to the corresponding hyperbranched polymer which contains unbound dye molecules. Further exploration would be required to develop a hyperbranched system suitable for photochromic switching.

7.4 Experimental Details

Materials. All monomers, solvents and reagents were purchased from Aldrich Chemical Co. at the highest available purity and were used as is unless otherwise stated. All commercially available momomers (MMA, EGDMA and PEGDMA) were filtered through aluminum oxide 90, activated basic (0.063 - 0.200 nm, Merck) to remove inhibitors before use. All chromatography was performed using silica gel

215 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

(Kieselgel Merck 60, 0.040 - 0.063 mm) and TLC was performed on Merck Silica

60F254 plates. The synthesis of CHRDMA, methyl 6-(methacryloyloxy)-2-(4-(2- (methacryloyloxy)ethoxy)phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate was described in the previous Chapter 6.

General Experimental Measurements. Gel permeation chromatography (GPC) was performed on a Waters 515 HPLC pump and Waters 717 Plus Autosampler equipped with Waters 2414 refractive index detector and 3 × Mixed-C (7.5 mm × 300 mm, 5 m particle size, linear molecular weight range 200 - 2,000,000) and 1 Mixed E PLgel column (7.5 mm × 300 mm, 3 m particle size, linear molecular weight range up to 30,000) from Polymer Laboratories. Tetrahydrofuran (THF) with a flow rate of 1.0 mL min-1 was used as eluent at 22 ± 2 °C. Molecular weights were calculated via calibration with narrow polydispersity polystyrene standards (Polymer Laboratories) ranging from 6 600 to 7.5 × 10 g/mol. Number (Mn) and weight-average (Mw) molecular weights were evaluated using Waters Millennium/Empower software. A third-order polynomial was used to fit the log M vs. time calibration curve, which was linear across the molecular weight ranges. 1H (400 MHz) and 13C NMR (100 MHz) spectra were obtained with a Bruker Av400 spectrometer at 25 °C. Spectra were recorded for samples dissolved in deuterated solvent and chemical shifts are reported as parts per million from external tetramethylsilane. Monomer conversions were obtained from the 1H NMR spectra. The resonances integrated to obtain conversions for polymerizations were the vinyl peaks for monomer only and vs. the peaks accounting for monomer and polymer. Thermal Analysis by Differential Scanning Calorimetry (DSC) was performed in order to determine the Tg of the polymers. This was carried out using a Mettler Toledo DSC821 machine with temperature and heat flow calibrated using indium and zinc as reference substances. Samples (~10 mg) were heated under nitrogen from -50 °C to 150

°C at 10 °C/minute. The Tg values were taken from the midpoints of the heat flow changes observed in the second heat cycle.

Synthesis of 2-(methylsulfanylthiocarbonyl)sulfanyl-2-cyano-4-methoxy-4- methylpentane, RAFT Agent. The general procedure described in literature19 was adapted to synthesize the title compound in which 2,2'-azobis(4-methoxy-2.4-dimethyl valeronitrile) (V-70, Wako Chemicals) and bis-(methylsulfanylthiocarbonyl) disulfide

216 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

1 were used as the reagents for radical coupling. H NMR (400 MHz, d6-acetone) : 1.28

(s, 3H, CH3), 1.42 (s, 3H, CH3), 1.99 (s, 3H, CH3), 2.15 - 2.18 (m, 1H, CHH), 2.64 -

2.68 (m, 1H, CHH), 2.78 (s, 3H, SCH3), 3.02 (s, 3H, OCH3).

Synthesis of ethylene glycol diacrylate, EGDA. Acryloyl chloride (15.40 g, 0.170 mol) dissolved in 50 mL of DCM was added drop-wise to a stirring solution of dried ethylene glycol (5 g, 0.081 mol) and TEA (20.5 g, 0.202 mol) in DCM (150 mL), whilst cooling with an ice bath. The solution was stirred under argon for 1 hour at room temperature. Water was then added to quench the reaction (100 mL) and the solution extracted with DCM (3 × 100mL). The combined organic extracts were dried with 1 anhyd. MgSO4 and the solvent removed under vacuum. As shown by H NMR analysis, the clear oil was of sufficient purity for subsequent use (9.6 g, 70%). 1H NMR (400

MHz, CDCl3) : 4.39 (s, 4H, O(CH2)2), 5.84 (d, 1H, J 1.5 Hz, =CH), 5.87 (d, 1H, J 1.5 Hz, =CH), 6.11 (d, 1H, J 10.6 Hz, =CH), 6.15 (d, 1H, J 10.2 Hz, =CH), 6.04 - 6.48 (overlapping doublets, 2H, J 17.2 Hz and 17.6 Hz, =CH) ppm.

Synthesis of methyl 6-(acryloyloxy)-2-(4-(2-(acryloyloxy)ethoxyphenyl)-2- phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate, CHRDA. Methacryloyl chloride (105 mg, 98L 1.12 mmol was slowly added to a stirring solution of methyl 6-hydroxy- 2-(4-(2-hydroxyethoxy)phenyl)-2-phenyl-2H-naphtho[1,2-b]pyran-5-carboxylate (0.250 g, 0.534 mmol) and TEA (136 mg, 187 L, 1.34 mmol) in DCM (15 mL). The solution was stirred under argon for 1 hour at room temperature. Water was then added (20 mL) and the solution extracted with DCM (3 × 20mL). The combined organic extracts were dried with anhyd. MgSO4 and the solvent removed under vacuum. Purification by column chromatography (silica gel 60, EtOAc/Hexane, 20/80) gave the product as a 1 pink crunchy solid (230 mg, 70%). H NMR (400 MHz, CDCl3) : 1.91 (s, 3H, =CCH3),

2.12 (s, 3H, =CCH3), 3.88 (s, 3H, COOCH3), 4.18 (t, 2H, J 4.76 Hz, CH2CH2OAr), 4.45

(t, 2H, J 4.76 Hz, CH2CH2OAr), 5.54 (m, 1H, =CH), 5.83 (br s, 1H, =CH), 6.09 (br s, 1H, =CH), 6.17 (d, J 10.0 Hz, 1H, pyran-H), 6.44 (br s, 1H, =CH), 6.85 (apparent d, J 8.8 Hz, 2H, ArH), 6.97 (d, 1H, J 10.0 Hz, pyran-H), 7.24 - 7.28 (m, 2H, ArH), 7.31 - 7.34 (m, 2H, ArH), 7.41 (apparent doublet, J 8.8 Hz, 2H, ArH), 7.47 - 7.58 (m, 3H, ArH), 7.72 (d, J 8.6 Hz, 1H, ArH), 8.35 (d, J 8.6 Hz, 1H, ArH) ppm. 13C NMR (100

MHz, d6-acetone) : 18.3, 18.5, 52.8, 63.9, 66.8, 83.6, 114.4, 115.2, 120.8, 121.9, 123.1, 123.4, 125.9, 127.1, 127.4, 128.1, 128.3, 128.4, 128.8, 128.9, 129.0, 129.1, 130.1, 136.5, 137.2, 137.8, 140.5, 145.9, 146.8, 159.3, 166.0, 166.2, 167.4 ppm.

217 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

Hyperbranched p(MMA) H1. A stock solution containing MMA (1.60 g, 15.98 × 10-3 mol), EGDMA (38 mg, 1.87 × 10-4 mol), CHRDMA (12.8 mg, 2.08 × 10-5 mol), RAFT Agent (42.8 mg, 1.60 × 10-4 mol) and AIBN (2.6 mg, 1.60 × 10-5 mol) was prepared in toluene (2.4 g). The final molar of MMA:CLA:RA:AIBN=100:1.3:1:0.1; EGDMA:CHRDMA=9:1 and MMA:CHRDMA = 100:0.13 The ampoules was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 20 hrs. The polymer was purified by twice precipitation into methanol and dried in a vacuum oven.

Hyperbranched p(MMA) H2. A stock solution containing MMA (1.60 g, 15.98 × 10-3 mol), EGDMA (20.6 mg, 1.04 × 10-4 mol), CHRDMA (62.81 mg, 1.04 × 10-4 mol), RAFT Agent (42.1 mg, 1.60 × 10-4 mol) and AIBN (2.6 mg, 1.60 × 10-5 mol) was prepared in toluene (2.4 g). The solution was added to an ampoule with the final molar of MMA:CLA:RA:AIBN=100:1.3:1:0.1; EGDMA:CHRDMA=1:1 and MMA:CHRDMA = 100:0.65. The ampoule was degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 23 hrs. The final polymer was purified by twice precipitation into methanol and dried in a vacuum oven.

Hyperbranched p(MMA) H3. A stock solution containing MMA (1.60 g, 15.98 × 10-3 mol), CHRDMA (10.8 mg, 2.08 × 10-5 mol), PEGDMA (115 mg, 2.08 × 10-4 mol), RAFT Agent (43 mg, 1.60 × 10-4 mol) and AIBN (2.8 mg, 1.60 × 10-5 mol) was prepared in toluene (1.6 g). The solution was added to an ampoule with a final molar ratio of MMA:CLA:RA:AIBN=100:1.3:1:0.1; CLA=PEGDMA and MMA:CHRMA=100:0.13. The ampoule was then degassed with three freeze-pump- thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 22 hrs. The final polymer was purified by twice precipitation into methanol and dried in a vacuum oven.

Linear p(MMA) copolymer L1. A stock solution containing MMA (1.60 g, 15.98 × 10-3 mol), CHRMA-1 (10.5 mg, 2.08 × 10-5 mol), RAFT Agent (42 mg, 1.60 × 10-4 mol) and AIBN (2.8 mg, 1.60 × 10-5 mol) was prepared in toluene (1.6 g). The solution was added to an ampoule with the final molar of MMA:CHRMA:RA:AIBN=100:0.13:1:1.3:0.1. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 22 hrs. The final polymer was purified by twice precipitation into methanol and

218 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

dried in a vacuum oven.

Linear p(MMA) copolymer L2. A stock solution containing MMA (1.60 g, 15.98 × 10-3 mol), CHRMA-2 (12.6 mg, 2.08 × 10-5 mol), RAFT Agent (42 mg, 1.60 × 10-4 mol) and AIBN (2.8 mg, 1.60 × 10-5 mol) was prepared in toluene (1.6 g). The solution was added to an ampoule with the final molar of MMA:CHRMA:RA:AIBN=100:0.13:1:1.3:0.1. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 22 hrs. The final polymer was purified by twice precipitation into methanol and dried in a vacuum oven.

Hyperbranched p(MA) H4. A stock solution containing MA (3.2 g, 37.17 × 10-3 mol), EGDA (38 mg, 3.27 × 10-4 mol), CHRDA (47.15 mg, 8.17 × 10-5 mol), RAFT Agent (97.92 mg, 3.71 × 10-4 mol) and AIBN (6.1 mg, 3.71 × 10-5 mol) was prepared in toluene (4.8 g). The solution was added to an ampoule with a final molar ratio of MA:CLA:RA:AIBN=100:1.1:1:0.1; EGDA:CHRDA=8:2 and MA:CHRDA = 100:0.22 The two ampoules were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 20 hrs. The final polymers were purified twice by precipitation into methanol and dried in a vacuum oven.

Linear p(MA) L3. A stock solution containing MA (1.60 g, 18.59 × 10-3 mol), CHRA (10.07 mg, 2.00 × 10-5 mol), RAFT Agent (492 mg, 1.90 × 10-4 mol) and AIBN (3.1 mg, 2.00 × 10-5 mol) was prepared in toluene (1.6 g). The solution was added to an ampoule with the final molar of MA:CHRA:RA:AIBN=99.9:0.10:1:1.3:0.1. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 7 hrs. The final polymer was purified by twice precipitation into methanol and dried in a vacuum oven.

Photochromic Analysis. Under continuous UV irradiation, the photochromic responses of the cast films or solutions were analyzed on a light table composed of a Cary 50 spectrophotometer for measuring the absorbance and a 160 W Oriel xenon lamp as the incident UV light source. A series of two filters (Edmund Optics 320 cut-off and bandpass filter U-340) were used to restrict the output of the lamp to a narrow band (350-400 nm). The samples were maintained at 20 °C and monitored at the maximum absorbance of the coloured form (max) firstly during UV-colouration and then the thermal decolouration period was monitored in the absence of UV irradiation. The times

219 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______used for colouration and decolouration were as follows (H4 p(MA) film: 820 seconds of colouration and 4000 seconds of decolouration; L3 p(MA) film: 808 seconds of colouration and 4000 seconds of decolouration; H2 p(MMA) film 2300 seconds of colouration and 1000 seconds of decolouration; H1 p(MMA) in toluene: 1740 seconds of colouration and 1200 seconds of decolouration; H3 p(MMA) in toluene: 1200 seconds of colouration and 620 seconds of decolouration; L1 p(MMA) in toluene: 1200 seconds of colouration and 850 seconds; L2 p(MMA) in toluene: 1200 seconds of colouration and 820 seconds).

Preparation of Photochromic Solutions: polymer samples were prepared in toluene with a concentration level of 15 mg of polymer per 4 mL of toluene. Photochromic kinetic testing was carried on the solutions containied in a quartz cell with a path legth of 1 cm.

Preparation of Photochromic Films. Hyperbranched polymers were dissolved in xylene and then cast onto glass slides. The films were left to dry at room temperature for 8 hrs and then dried in a vacuum oven at 100 ºC overnight.

7.5 References

(1). Lyubimov, A. V.; Zaichenko, N. L.; Marevtsev, V. S. J. Photochem. Photobiol., A 1999, 120, 55-62. (2). Flory, P. J., Molecular Weight Distributions in Nonlinear Polymers and the Theory of Gelation. In Principles of Polymer Chemistry, Cornell University Press: New York, 1953; pp 347-392. (3). Matsumoto, A. Synth. Photosynth. 1995, 123, 41-80. (4). Voit, B. I.; Lederer, A. Chem. Rev. 2009, 109, 5924-5973. (5). O'Brien, N.; McKee, A.; Sherrington, D. C.; Slark, A. T.; Titterton, A. Polymer 2000, 41, 6027-6031. (6). Isaure, F.; Cormack, P. A. G.; Graham, S.; Sherrington, D. C.; Armes, S. P.; Butun, V. Chem. Comm. 2004, 1138-1139. (7). Liu, B. L.; Kazlauciunas, A.; Guthrie, J. T.; Perrier, S. Macromolecules 2005, 38, 2131-2136. (8). Liu, B. L.; Kazlauciunas, A.; Guthrie, J. T.; Perrier, S. Polymer 2005, 46, 6293- 6299.

220 Chapter 7. Photochromic Behaviour within Hyperbranched Polymers. ______

(9). Vo, C. D.; Rosselgong, J.; Armes, S. P.; Billingham, N. C. Macromolecules 2007, 40, 7119-7125. (10). Konkolewic D.; Gray-Weale A.; Perrier, S., Polym. Chem., 2010, 1, 1067–1077. (11). Rosselgong J.; Armes S.P.; Barton W.R.S.; Price D. Macromolecules 2010, 43, 2145–2156. (12). Mark, E. R.; Stephen, R. Polym. Chem. 2010, DOI: 10.1039/c0py00154f. (13). Yates, C. R.; Hayes, W. Eur. Polym. J. 2004, 40, 1257-1281. (14). Kurmaz, S. V.; Kochneva, I. S.; Ozhiganov, V. V.; Grachev, V. P.; Aldoshin, S. N. Dokl. Phys. Chem. 2007, 417, 328-331. (15). Kurmaz, S. V.; Kochneva, L. S.; Perepelitsina, E. O.; Korolev, G. V.; Grachev, V. P.; Aldoshin, S. M. Russ. Chem. Bull. 2007, 56, 197-204. (16). Li Y. T.; Ryan A. J.; Armes S.P. Macromolecules 2008, 41, 5577-5581. (17). Munakata, Y.; Tsutsui, T.; Saito, S. Polymer J. 1990, 22, 843-848. (18). Miyazaki, K.; Horibe, T. J. Biomed. Mater. Res. 1988, 22, 1011-1022. (19). Moad, G.; Chong, Y. K.; Postma, A.; Rizzardo, E.; Thang, S. H. Polymer 2005, 46, 8458-8468.

221 8 The Application of a Photochromic Probe to Monitor the Self-Assembly of Block Copolymers in Water.

8.1 Introduction

The use of polymers as drug carrier systems is a promising avenue for the development of targetted therapeutic treatments.1 Amphiphilic polymers are particularly useful since they can take up different nano-particulate forms in water of varying sizes and shape.2 One pertinent example is the self-assembly of unimers into micelles, which can be triggered by an external stimulus such as temperature, pH or light.3 In aqueous medium poly(N-isopropyl acrylamide), p(NIPAM), undergoes a reversible phase transition at its lower critical solution temperature (LCST). When heated above this temperature, individual polymer chains can undergo a collapse from water-swollen coils, to form multi-chain macroscopic aggregates or dispersed mesophases.4-6 Typically this occurs between 25-32 °C, depending on composition, architecture and end group structure of the polymer chains.7,8 A block copolymer composed of a section of p(NIPAM) and a second section of another water-soluble polymer can undergo a reversible temperature-induced unimer-to-micelle assembly at the LCST.9,10 The fundamentals of such thermally-triggered phase transitions and their application to different technologies continue to attract interest.11-16 Various types of light-sensitive molecular probes have become available for investigating complex polymer properties such as phase changes.17,18 Fluorescent probes19 for example, have been used to detect micelles,20-22 the kinetics of merging and chain exchange between p(NIPAM) mesoglobules,6 crystallization in polymer blends,23 nano-scale segmental dynamics in amorphous polymer matrices24,25 and glass transition dynamics26 in polyolefins27. Conformational changes displayed by probe molecules have also allowed visualization of the local free volume available in various polymer matrices.28 My interest has been focused on photochromic dyes which are molecules that reversibly isomerize when stimulated with light.29,30 For spirooxazine and chromene dyes, this inter-conversion occurs between a colourless form that has an orthogonal, closed conformation and a coloured merocyanine state that is planar, open and conjugated throughout. Colouration is stimulated by UV light and involves an Chapter 8. The Application of a Photochromic Probe... ______electrocyclic ring opening reaction followed by a rate limiting bond rotation. On the exclusion of UV light, thermal decolouration occurs spontaneously in the dark through the reverse process (Figure 1).

Figure 1. Spirooxazine photochromic transformation.

The photochromic transformation involves substantial spatial movement, requiring at least one bond rotation to relocate bulky groups from one side of the molecule to the other. Overall the molecule’s freedom to move is greatly affected by rigidity and the free volume available in the surrounding environment. The relationship between the photochromic dye and the surrounding matrix environment holds significance on many levels and has been the focus of several reviews.31-33 These concepts have beeb applied to control switching speed in a glassy rigid media by modulating the viscosity of the dye’s local environment.34,35 Because photochromic molecules are inherently sensitive and responsive to their surroundings, this also presents a practical opportunity to explore the characteristics of their local environment. The application of photochromism to probe environmental characteristics has in fact appeared in various publications with studies directed at investigating a range of material properties. Different experimental methods were compared by Jansen et al.36 for the characterization of the overall free volume in amorphous and glassy perfluoropolymers, which included a photochromic azobenzene probe method. Krongauz used a photochromic spiropyran to probe the strain behaviour in a .37 As part of a fluorescent modulation study, Harbron noted that the thermal decolouration kinetics and absorption spectrum displayed by a spirooxazine open form, when contained inside conjugated nanoparticles, as compared to analogous polymer films, could be used to probe their environment.38 Investigations into the nano-structuring of polar and nonopolar domains in ionic liquids have also been carried out using spiropyran and spiroxazine dyes.39 Diarylethene photochromics, which have fluorescent and solvatochromic coloured

224 Chapter 8. The Application of a Photochromic Probe... ______forms, have been applied as probes for investigating the polarity of their microenvironment as well as markers for imaging biomolecules.40,41 In this chapter I show that the nano-scale alterations in polymer phases occurring during the self-assembly of the block copolymers into micelles can be detected through the kinetic responses displayed by a spirooxazine photochromic molecule. In this context, I was able to investigate the assembly of various amphiphilic block copolymers in aqueous solutions. The spirooxazine dye was covalently attached in different locations on the macromolecular chain of the thermo-responsive block copolymer section and its response was examined with respect to temperature. The corresponding unconjugated dye was also encapsulated within self-assembled block copolymer micelles and its behaviour examined with respect to micelle concentration.

8.2 Results and Discussion

There are several factors that need to be considered when applying a photochromic dye for probing the properties of the polymer in which they are incorporated.23 Firstly, in order for the information that is obtained to be reliable, the bulk properties of the polymer medium should remain largely unaffected by the photochromic inter- conversions. I considered a spirooxazine dye to be appropriate since its photochromic transformations do not elicit other photo-responses in the material that could potentially interfere with the experiment. For example, spiropyran and azobenzene photochromics undergo significant polarity changes when they switch forms which can directly trigger property changes, such as reversible micelle disruption, aggregation or swelling phenomena, as demonstrated in several studies.42-44 Furthermore, only dilute solutions of the SOX were necessary for measurements (~110-4 M) which also reduces the possibility of dye molecules impacting to affect the bulk properties of the polymer. The merocyanines of nitro-substituted spiropyrans are predominantly zwitterionic in their ground states and effectively stabilized in a polar environment.45,46 This means that when they are dissolved in aqueous or polar solutions at room temperature, measurable amounts of their ring opened forms are generated to produce substantial colour even before UV irradiation (reverse photochromism).47-49 Whilst such thermochromic effects have been applied in novel ways,50 it would have proved counter-productive in these experiments. In comparison, a great majority of spirooxazine dyes have weakly polar, quinoidal

225 Chapter 8. The Application of a Photochromic Probe... ______open forms.51,52 This is supported by a positive solvatochromic effect, seen as a bathochromic shift of the wavelength of coloured forms with an increase in polarity. In this regard, the spirooxazine dye chosen for this study served well, being able to produce measurable levels of absorbance intensity only under the action of UV irradiation, with insignificant baseline colour.

O O O N N O NH O O S O O S S O 1 N S S N a S O b SOX-p(NIPAM)-b-p(NAM) N O (i) NIPAM (ii) NAM N O NH a=87; b=220 1,4-dioxane, AIBN, 60° C SOX-RAFT Mn 38,400 g/mol

NH O O HO S b S S 2 O O O a c co b N O p(NIPAM)- -p(SOX)- -p(NAM) HO S S a=92; b=243; c=1.2 O S O O M O N n 41,300 g/mol O NH N N O N O N O (i) NAM (ii) SOX-ACR (1%) NIPAM (99%) 3 co b 1,4-dioxane, AIBN, 60° C NH p(NIPAM)- -p(SOX)- -p(NAM) O O a=93; b=115; c=1.3 O S M 26,800 g/mol b S S n O HO O a O c O N O S S HO S 4 O N p(NIPAM)-co-p(SOX)-b-p(NAM)

O a=93; b=178; c=1.6 N Mn 34,080 g/mol

Scheme 1. Synthesis of p(NIPAM)-block-p(NAM) diblock copolymers 1-4; p(NIPAM) = poly(N-isopropyl acrylamide); p(NAM) = poly(N-acryloyl morpholine); p(SOX) = polymerized spirooxazine; Refer to Table 1 for polymer characteristics.

8.2.1 RAFT Synthesis of Polymers.

My initial goal was to synthesise linear block copolymers containing a thermally responsive p(NIPAM) segment. Various poly(N-isopropyl acrylamide)-block- poly(N-acryloyl morpholine block copolymers, p(NIPAM)-b-p(NAM), were suitably prepared. Their synthesis was carried out in sequential steps using reversible addition- fragmentation chain transfer (RAFT) polymerization,53 as shown in Scheme 1. RAFT is particularly advantageous due to its compatibility with a wide range of functionality in monomers, solvents and initiators. It allows special architectures like block copolymers to be accessed with controlled molecular weights and compositions of block sections, narrow polydispersities (PDI) and well defined end-groups. Table 1 shows the specific characteristics of polymers synthesized, which are referenced and

226 Chapter 8. The Application of a Photochromic Probe... ______discussed throughout the text. The polymerizations were carried out homogenously in dioxane at 60 C with AIBN, using approximate [monomer] / [RAFT agent] ratios of 250 for NIPAM and 95 for NAM polymerizations. Use of the SOX-functional RAFT agent (SOX-RAFT) allowed the dye to be precisely located at the end of the p(NIPAM) block section as in copolymer 1, SOX-p(NIPAM)-b-p(NAM). In block copolymers 2-4, SOX moieties were incorporated within the p(NIPAM) section by using a SOX-functional monomer, SOX-ACR. In this case the initial polymerizations were carried out with NAM instead of NIPAM and, by using an appropriate RAFT agent, this allowed a hydrophilic group to be located at the end of the water soluble NAM section of polymer chains. The structural composition and sequential block extension of the copolymers were confirmed by 1H NMR and gel permeation chromatography (GPC) respectively. All samples displayed narrow molecular weight distributions with a PDI < 1.3.

Table 1. Polymers synthesized and investigated in the study.

b c d Sample Polymer Structure Mn PDI

1 SOX-p(NIPAM)220-b-p(NAM)87 38,400 1.10

2 p(NIPAM)243-co-p(SOX)1.2-b-p(NAM)92 41,300 1.16

3 p(NIPAM)115-co-p(SOX)1.3-b-p(NAM)93 26,800 1.16

4 p(NIPAM)178-co-p(SOX)1.6-b-p(NAM)93 34,080 1.22

5 p(BA)89-b-p(NAM)93 24,880 1.20

6 SOX-p(BA)135-b-p(NAM)104 17,980 1.04

Control p(SOX)1-co-p(NAM)93 13,900 1.03

Control p(SOX)1.1-co-p(NAM)93 13,600 1.05

Control SOX-p(NAM)84 12,450 1.04 a Polymer composition estimated by 1H NMR analysis. b Average molecular weight in g/mol estimated by 1H NMR c PDI = polydispersity index as determined by GPC (SEC) using DMF as eluent and polystyrene as standards.

227 Chapter 8. The Application of a Photochromic Probe... ______

8.2.2 Thermally-Induced Self-Assembly.

The synthesized block copolymers were then dissolved in water and their self- assembly profiles analysed as a function of temperature using dynamic light scattering (DLS). Upon heating the solutions from 20 C an increase in hydrodynamic diameters,

Dh, were observed for each, representative of thermally-induced micelle formation and growth. During this process the p(NIPAM) section forms the hydrophobic inner core of the micelles, along with the SOX, and the p(NAM) section forms the outer hydrophilic corona. It is well known that amphiphilc block copolymers can self-assemble into an array of nano-scale structures in solvents that are selective for one of the blocks, including spherical micelles, cylindrical or wormlike micelles, and bilayer vesicles. In solution this is controlled by the balance between different factors: the degree of stretching of the core-forming blocks, the interfacial tension between the micelle core and the solvent outside the core, and the repulsive interactions between corona-forming chains.54 The morphology of the aggregates is therefore influenced by the structural features of the block copolymers.55 This includes the polarity, rigidity and the relative lengths of each block, as well as the overall molecular weight of the block copolymer.56 Moreover, the preparation conditions, polymer concentration and external factors like temperature also have a direct influence.57 Taking into consideration these interplaying factors, a large number of publications have appeared over the past decade exploring the mechanisms and dynamics involved in the formation of block copolymer morphologies in solution.58-60 Cryo-TEM analysis was carried out on some of the solutions, however, since the samples could only be equilibrated to 25 C prior to freezing, this analysis merely served to confirm the presence of micelles. More exhaustive TEM imaging would be needed in order to fully explore the possibility of thermally-induced morphological transitions.61 Iimages for 1 showed elongated micelles in coexistence with spherical and fused micellar structures. Some also displayed junctions and spherical end-caps (Figure 2 left). These morphological features are not uncommon, and have been reported for many block copolymers.62 The tendency of polymeric micelles to become kinetically trapped in non-equilibrium states, especially for those containing rigid hydrophobic cores, is also thought to give rise to different hybrid morphologies.63,64 The SOX end- functional block copolymer, poly(n-butylacrylate)-block-poly(N-acryloyl

228 Chapter 8. The Application of a Photochromic Probe... ______morpholine), which is discussed below, showed similar morphological features (Figure 2, right).

Figure 2. Cryo-TEM images recorded from a 0.7 wt% aqueous solution of SOX- p(NIPAM)-b-p(NAM) 1 (left) and a 0.1 wt % aqueous solution of SOX-p(BA)-b- p(NAM) 6 (right) revealing different morphological features.

8.2.3 Thermal Decolouration Kinetics.

The absorption of UV light by the photochromic dye results in the cleavage of its spiro carbon-oxygen bond, followed by rearrangement and rotation of bonds. This process leads to several planar and highly conjugated open forms, known as merocyanines. The existence of an isomeric distribution made up of several merocyanine forms in solution has been confirmed independently using Raman and absorption spectroscopy as well as NMR.65-67 In these merocyanine structures the three ethylenic bonds can exhibit either the cis (C) or trans (T) conformation. While eight steroisomeric forms are conceivable, due to energetically constraints only four transoid-type isomers are possible (TTT, TTC, CTT, CTC). For SOX, the most stable forms which contribute to the equilibrium mixture have been determined to be TTC and CTC isomers.47 Their energetically distinct stereoisomer populations are produced in different proportions and are thought to undergo separate uni-molecular decolouration processes for ring closure. Decolouration can therefore be accounted for in solution by using a biexponential decay equation.51,67,69 The proportion of each isomer type depends on substitution, solvent and irradiation conditions, however, one isomer population normally accounts for a great majority of the colour and decay.

229 Chapter 8. The Application of a Photochromic Probe... ______

Taking these factors into consideration, the decolouration kinetics for the p(NIPAM)-b-p(NAM) aqueous solutions were spectroscopically determined as a function of temperature. This was done by monitoring the evolution of colour at the

max (610 nm) of the open form: initially for approximately 5 minutes, whilst the sample is UV-irradiated, and then for a further 5-10 minutes as the sample fades in the dark. The collected decay data at each temperature was then fitted to the following biexponential equation to obtain the thermal (first-order) rate constants for ring- closure:    k1t  k2t A(t) A1e A2e where A(t) is the optical density at max of the open form; A1 and A2 are the contributions to the initial optical density A0, and k1 and k2 are the decay rate constants. The data fitting gave correlation coefficients of greater than 0.999 using more than 400 data points. In some instances the data could only be fitted accurately to a single exponential decay, instead of two. Overall, the k1 rate constant was found to contribute to a majority of the measured decay (80-100 %), as evaluated from the final

A1/A2 ratios, and was therefore selected to represent the decolouration of photochromic solutions.

8.2.4 Photochromic Probing.

The growth in hydrodynamic diameters, Dh, and the measured decolouration rate constants, k1, were plotted with respect to temperature (Figures 3 and 4 below). The latter are in fact Arrhenius plots (with 1/T axis reversed) illustrating the effect of temperature on the rates of ring-closure. Like any other conventional chemical reaction, these were expected to be linear throughout, however, the SOX- functionalized p(NIPAM)-b-p(NAM) copolymers showed a distinct deviation from linearity. Furthermore, this was found to occur within a temperature range which corressponded with the growth of micelles, as measured via dynamic light scattering (DLS). On the whole the deviation was far more pronounced for block copolymer 2, especially when compared to SOX end-functional block copolymer 1. When SOX was incorporated into shorter p(NIPAM) block sections, as in 3 and 4, these also showed stronger responses compared to 1. The placement of SOX at the terminus of the

230 Chapter 8. The Application of a Photochromic Probe... ______polymer chain along with an extra benzene ring separating it from the p(NIPAM) block in 1 could account for the weaker response. In contrast, a higher level of insulation is provided by the architecture of 2-4 where SOX is copolymerized within the p(NIPAM) and this is especially the case for 2 which contains the largest block section. The nature of the -end group of the polymers could also have an effect on the dye’s thermodynamic behaviour to cause differences in the profiles. Overall, the dependency of the thermo-kinetic responses on the dye’s location and length of the thermo-responsive block emphasizes a strong sensitivity of SOX to its immediate environment.

Figure 3. Thermal assembly profiles for micelles as a function of temperature (top) vs. Arrhenius plots (bottom with 1/T scale shown in reverse order) for spirooxazine end-functional block copolymer 1 and spirooxazine block copolymer 2.

Environmental factors can have a considerable effect on thermal relaxation dynamics therefore an understanding of these could help to explain the anomalies displayed in each of the thermo-kinetic profiles. One such factor is the effect of environmental polarity.70 The interactions occurring between the solvent and both the ground state of the merocyanine open form and the transition state to the closed form have been closely studied by several authors.47,52 It is believed that the light-induced

231 Chapter 8. The Application of a Photochromic Probe... ______opening of the oxazine ring yields a short-lived transient species that rearranges to give a coloured merocyanine with a predominantly quinoidal ground-state form.71 A red (bathochromic) shifting of the absorption maximum in solvents of increasing polarity (i.e. positive solvatochromism) results from a transition state that is stabilized by solvent polarity more so than a weakly polar ground state.51,52,69,72 This can also result in an increase in the rate of decolouration with an increase in solvent polarity as general trend. I therefore considered the affect of an overall change in polarity occuring in the local environment of SOX during heating, on its thermo-kinetic responses.

Figure 4. Thermal assembly profiles for micelles as a function of temperature (top) vs. Arrhenius plots (bottom, with 1/T scale shown in reverse order) for spirooxazine end-functional block copolymer 3 and spirooxazine block copolymer 4.

Studies on spirooxazine-doped sol-gel matrices have discussed the effect of polarity on the thermal behaviour of different spirooxazine dyes.73,74 One notion is that a more polar micro-environment can favour the production of a more polar open form which then affects the thermal equilibrium between closed and coloured forms. This is highly dependant on the substitution pattern of the SOX, such as the presence of electro-donating groups in the oxazine moiety, and is evidenced most strongly by 232 Chapter 8. The Application of a Photochromic Probe... ______reverse photochromism. I did not observe the production of colour before irradiation, either below or above the LCST of the p(NIPAM) to suggest that this was an intervening factor. Investigations by Lee et al. point to more pertinant thermo-kinetic factors for explaining spirooxazine behaviour with respect to polarity.75 Thermal decolouration was investigated at various temperatures and in different solvents using laser flash photolysis. The thermal decay rate was found to generally increase with solvent polarity. Both an increase in the activation enthalpy and activation entropy were also noted with an increase in the solvent polarity, and interpreted in terms of a dissociation of either a solvated merocyanine complex and/or an ordered solvent structure around merocyanine forms on progression to the closed form. The slower reaction rate observed in non-polar solvents was thought to arise from a more ordered transition state.

Whilst I did not observe any coincident spectral shifts in max of the SOX coloured form during heating, to signify preferential stabilization of either the ground state or the transition state, some change is expected to occur in the polarity of its local environment. At low temperatures, water molecules are largely hydrogen bonded to p(NIPAM), providing it with a hydration layer which renders it soluble in water. On heating the aqueous solutions of the block copolymers through the LCST of p(NIPAM), an overall change is expected to occur as water molecules are expelled from the NIPAM units. During this process, a change in the solvation and order of a polar transition state could occur on heating leading to a measurable change in the behaviour of SOX. As chains associate and reorganize there is also the possibility that hydrophobic interactions may occur between SOX and NIPAM units, as well as between SOX units themselves. However the occurance of significant photochromic aggregation was ruled out since this is also associated with spectral shifts and this were not observed. It has been reported that the polarity of the microenvironment dominates the decolouration kinetics only when the viscosity of the medium is kept constant.76 In combination with potential stabilizing merocyanine-matrix interactions arising through environmental polarity, the kinetic parameters of thermal fade are also known to be highly dependant on steric constraints arising from the rigidity, viscosity and limited free volume available in the surrounding environment.

233 Chapter 8. The Application of a Photochromic Probe... ______

An obvious effect of the rigidity of the surrounding matrix for a photochromic probe is a decolouration rate that is markedly slower than in solution.32 The thermodynamic parameters for spirooxazine decolouration have been studied with a comparative investigation between a rigid polymer matrix and that of solution.77 The matrix environment was found to have the effect of reducing both the activation energy and the pre-exponential factor for thermal decolouration. However, the notable decrease in fade kinetics observed in a rigid matrix was found to be associated far more with a marked decrease in the pre-exponential factor and with exceptionally high negative activation entropies. A decrease in torsional freedom of the transition state was thought to outweigh any positive contributions arising from randomization of surrounding molecules around open forms. Fluorescence spectroscopy has also been used to probe the behaviour of mesoglobular phases formed upon heating p(NIPAM).6 Fluorescence anisotropy measurements conducted on fluorescently labeled p(NIPAM) gave an indication of the rotational freedom of the pendant dye in a given environment and was related back to the micro-viscosity of the phase in which it was dissolved. The results of indicated that samples heated within the 31- 36 °C temperature range consisted of fluid-like particles able to merge and grow in size. At higher temperatures the mesoglobules acted as rigid spheres unable to merge upon collision. It was also suggested that on further heating, of the mesoglobule core can also occur, enhancing particle stability, rigidity and resistance toward merging.78 Interestlingly, my DLS profiles suggested analogous behaviour to p(NIPAM) mesoglobules: a process of growth, via particles exchanging and merging, followed by stabilization of the micelles on futher heating, seen as a levelling out of Dh values. Within the temperature domain that showes the greatest micelle growth, corresponding Arrhenius plots also show a variation in their slope, which is a measure of the activation energy of thermal decolouration. This can be related back to what is occuring during the assembly process. Associative contacts between the newly exposed NIPAM units lead to chain contraction and eventually phase separation of the block sections. This would be experienced by the photochromic as a change in the local viscosity which directly affects the molecule’s freedom to move during decolouration. During the transition, the slope of the Arrhenius plot appears to level out the most, which means that the decolouration rate is less affected by increases in temperature. Once the micelles are stabilized, the local matrix environment

234 Chapter 8. The Application of a Photochromic Probe... ______surrounding SOX would also be expected to be relatively constant so the original gradients are then reinstated. However, the plots then intercept the y axis at a lower value. Therefore, a marked decrease in the pre-exponential factor is really the ultimate effect of micelle formation. This is particularly evident for the plots of 2-4 which show the largest drop. Again, as noted previously, because SOX is copolymerized into these polymers, they are likely to experience a higher level of contact with surrounding NIPAM units, compared to 1. Therefore a more significant impact would be made by the changes that p(NIPAM) undergoes on heating. This is especially the case for 2 in which each SOX unit is surrounded by the greatest number of NIPAM units. Overall, the aforementioned views support the observed trends observed for the block copolymers. An increase in rigidity, as well as a reduction in the polarity on heating could intervene to affect photochromic behaviour. Both are likely to contribute a transition state that has less freedom to move or is more ordered overall during the process of phase separation and self-assembly.

Figure 5. Arrhenius profiles for control polymers which did not contain p(NIPAM) within their structures. 235 Chapter 8. The Application of a Photochromic Probe... ______

To exclude the possibility of other factors causing the observed anomalies with temperature p(NAM) control structures were also prepared which did not contain any NIPAM. The Arrhenius profiles for each of these control polymers in water were linear throughout and the structures did not micellize on heating (Figure 5). Hence, the origin of non-linearity in the Arrhenius profiles for the SOX-functionalized p(NIPAM)-b-p(NAM) blocks can be ascribed to the temperature-induced change in phase of p(NIPAM) which occurs during micelle assembly. It is well known that the thermal back reaction has a direct affect on the photo- colouration process by influencing the amount of photo-convertible colourless form available during steady-state irradiation.79 Overall, this means that the sensitivity of the decolouration rate to temperature also affects colour intensity. In solution some photochromic dyes produce a colour change that is barely detectable at room temperature limiting their practical utility. The micellar solutions prepared here were optically clear, consistent with their nano-scale proportions and displayed both a bright and long-lived colour even when heated above room temperature. In fact, copolymer 2 displayed almost complete thermal insensitivity in the region between 28-32 ºC (Figure 3, bottom right), which is striking in contrast with the strong sensitivity to temperature displayed by the free dye when dissolved in an organic solvent. The encapsulation of SOX within a p(NIPAM) micelle core therefore also provides an interesting avenue to regulate photo-colouration and thermal decolouration responses in aqueous media. To probe further the assembly of amphiphilic block copolymers in water using photochromism, a different set of polymers were synthesized: poly(n-butyl acrylate)- block-poly(N-acryloyl morpholine) block copolymers, p(BA)-b-p(NAM) (Figure 6). Here, the aim was to investigate the formation of micelles in water as a function of polymer concentration. This was explored by measuring the kinetics of decolouration of a hydrophobic dye, SOX-PROP, whilst being incorporated within the core of micelles. The micelles were assembled out of p(BA)-b-p(NAM), 5, by adding water slowly to solutions containing different concentrations of the polymer in dioxane. SOX-PROP was then loaded into the micelles and DLS carried out on each solution to determine whether micelles were present. The ring-closure rate constants k1 for the same aqueous solutions were spectroscopically determined and plotted as a function of polymer concentration, as shown in Figure 6.

236 Chapter 8. The Application of a Photochromic Probe... ______

Figure 6. The self-assembly of amphiphilic poly(n-butyl acrylate)-block-poly(N- acryloyl morpholine) block copolymers, p(BA)-b-p(NAM): decolouration rate constant (k1) of SOX-propionate (SOX-PROP) as a function of polymer concentration.

A deflection in slope commences at 1.2 mg/ml, which suggests that a change in local environment has occurred for SOX-PROP. At polymer concentrations below this point micelles were unable to be detected by DLS due to poor scattering intensities (refer to Appendix 6 for tabulated data). SOX end-functionalized block copolymer 6 was synthesized for comparison and subsequently assembled in water in the same manner using a concentration level well above its critical micelle concentration (4 mg/ml, giving defined particles of approx. 50 nm by DLS and defined assemblies of approx 70 nm using Cryo-TEM, Figure 2 right). End functionality guarantees that the SOX moieties of 6 are located within the fluid p(BA) core of the formed micelles and this would be expected to to give faster kinetics overall, compared to the water phase. The kinetics that it displayed were in fact found to closely approach that of 5 at a similar concentration indicating that for 5, SOX had been taken up by the micelles. These aspects imply the origin of the deflection point in Figure 6 is the incorporation of dye molecules within p(BA)-b-p(NAM) micelles and therefore representative of the minimum concentration of polymer that is required for micelle assembly.

237 Chapter 8. The Application of a Photochromic Probe... ______

8.3 Conclusion

In conclusion, I have shown that the strong sensitivity of photochromic dyes to their surroundings can be applied to probe their local environment. In this study this approach was used to monitor the formation of micelles since the aggregation and phase separation of polymer sections during their assembly leads to measurable changes in the dye’s environment and therefore behaviour. This aspect could be further exploited in other materials to investigate other nano-scale interactions and dynamic behaviour. The compatibility of the conjugates with aqueous media also makes them interesting candidates for probing biochemical processes in aqueous media.

8.4 Experimental Details

Materials. All chemicals (reagents, monomers and solvents) used for synthesis were of the highest purity available and used as received unless otherwise stated. All reagents were purchased from Aldrich Chemical Co. unless otherwise stated. Chromatography was performed using silica gel (Kieselgel Merck 60, 0.040 - 0.063 mm) and TLC was performed on Merck Silica 60F254 plates. N-acryloyl morpholine (NAM) was purified by passing through basic alumina (70-230 mesh) immediately prior to use. 2,2 -Azobis(isobutyronitrile) (AIBN) was obtained from TCI-EP and recrystallized from MeOH before use.

General Experimental Measurements. Gel permeation chromatography (GPC) was performed on a system comprising a Waters 590 HPLC pump and a Waters 410 refractive index detector equipped with 3 × Waters Styragel columns (HT2, HT3, HT4, each 300 mm × 7.8 mm providing an effective molecular weight range of 100- 600000). The eluent was N,N-dimethylformamide (DMF) (containing 0.045% w/v

LiBr) at 80 °C (flow rate: 1 mL min-1). Number (Mn) and weight-average (Mw) molecular weights were evaluated using Waters Millennium software. A polynomial was used to fit the log M vs. time calibration curve, which was linear across the molecular weight ranges. 1H (400 MHz) and 13C NMR (100 MHz) spectra were obtained with a Bruker Av400 spectrometer at 25 °C. Spectra were recorded for samples dissolved in deuterated solvent and chemical shifts are reported as parts per million from external

238 Chapter 8. The Application of a Photochromic Probe... ______tetramethylsilane. Monomer conversions for p(NIPAM) were obtained from the 1H NMR spectra.

Preparation of aqueous solutions for DLS and Photokinetic Experiments. Photochromic polymers were dissolved into MilliQ water with concentrations in the order of (1.0 - 1.3) × 10-4 M. This corresponded to an absorbance range of 0.1 - 1.9, a suitable range for the detector. This also corresponded to a concentration > 3.5 mg/mL which was above the critical micelle concentration and therefore appropriate for Dynamic Light Scattering (DLS) measurements.

Photokinetic Experiments. A schematic of the apparatus used is described elsewhere.80 The photochromic transitions were monitored via absorbance measurements using a Cary 50 UV/Vis spectrophotometer. A 160 W Oriel xenon lamp was used to irradiate homogeneously (at a right angle) approx. 1 ml of photochromic polymer solution contained in a quartz cell (1 cm path length). A series of two filters (Edmund Optics WG320 and Edmund Optics band-pass filter U-340) were used to restrict the output of the lamp to a narrow wavelength band (350-400 nm). The temperature of the solution was controlled using a Peltier thermoelectric cooling device. The sample was maintained at the specified temperature for 20 minutes to reach thermal equilibrium. Absorbance measurements were monitored at the maximum absorbance wavelength of the coloured form (610 nm). The increase in absorbance value was firstly followed during continuous irradiation for 5 minutes in order to attain a photo-steady state. The thermal ring-closure reaction (decolouration period) was then followed in the dark for a further 5 minutes by monitoring the disappearance of the coloured form on removal of the irradiating light. The kinetic rate parameters for ring closure were determined at each temperature by fitting the recorded absorbance signals, collected every 0.1 - 0.3 s, to biexponential kinetics

(refer to discussion for equation). The rate constants, k1, for each temperature were determined with a correlation coefficient of greater than 0.999 using more than 400 data points.

Cryo-Transmission Electron Microscopy (Cryo-TEM). A laboratory-built humidity-controlled vitrification system was used to prepare the nanoparticles for imaging in a thin layer of vitrified ice using cryo-TEM. Humidity was kept close to 80% for all experiments, and ambient temperature was 22°C. Sample 1 was

239 Chapter 8. The Application of a Photochromic Probe... ______equilibrated at 25°C prior to grid preparation. 200-mesh copper grids coated with perforated carbon film (Lacey carbon film: ProSciTech, Qld, Australia) were used for all experiments. Grids were glow discharded in nitrogen for 5 seconds immediately before use. 4L Aliquots of the sample were pipetted onto each grid prior to plunging. After 30 seconds adsorption time the grid was blotted manually using Whatman 541 filter paper, for approximately 2 seconds. Blotting time was optimised for each sample. The grid was then plunged into liquid ethane cooled by liquid nitrogen. Frozen grids were stored in liquid nitrogen until required. The samples were examined using a Gatan 626 cryoholder (Gatan, Pleasanton, CA, USA) and Tecnai 12 Transmission Electron Microscope (FEI, Eindhoven, The Netherlands) at an operating voltage of 120KV. At all times low dose procedures were followed, using an electron dose of 8-10 electrons/Å2 for all imaging. Images were recorded using a Megaview III CCD camera and AnalySIS camera control software (Olympus.) using magnifications in the range 60 000x to 110 000x.

DLS Measurements. Polymer solutions were prepared as described above, with a concentration 3.5 – 4.5 mg/ml in MilliQ water. Each solution was passed through a 0.45 m filter before carrying out micelle size determination in a Zetasizer-Nano instrument (Malvern, UK). The analysis was performed on solutions equilibrated at each sequential temperature for 20 minutes. The diameter (nm) values were calculated using the intensity size distributions fitted by method of cumulants. The mean diameter and polydispersities (PDI) were presented, based on 5 determinations at each temperature. The results of all photo-kinetic experiments and DLS measurements are contained in the Appendix 6, pages A28-A33.

Capture of SOX-PROP into micelles formed from block copolymer 5. Different quantities of polymer 5 (ranging from 1.1 - 19.2 mg) were dissolved into dioxane (500 l). Milli Q water (4 mL) was then added dropwise to each of the stirring solutions. A set quantity (60 L) of a 0.01 M solution of SOX-PROP in dioxane was then added dropwise using a microsyringe. Dioxane was purposefully not removed to maintain it at a constant level in each sample. DLS was then carried out on each solution to determine if micelles had been formed. The kinetics for ring-closure for the same aqueous solutions were then spectroscopically determined and plotted as k1 values.

240 Chapter 8. The Application of a Photochromic Probe... ______

The results of corresponding photo-kinetic and DLS measurements are contained in Appendix 6.

Self-assembly of SOX-p(BA)135-b-p(NAM)104, 6, in water. 19.8 mg of polymer 6 was dissolved into dioxane (500 l). Milli Q water (4 mL) was then added dropwise to the stirring solution. DLS was then carried out to determine micelles size. DLS was then carried out on each solution to determine if micelles had been formed. The kinetics for ring-closure for the same aqueous solution was then spectroscopically determined and plotted as a k1 value. The results of corresponding photo-kinetic and DLS measurements are contained in the Appendix 6.

Synthesis of RAFT Agents, SOX derivatives and Polymers:

Synthesis of 4-(n-Butylsulfanylthiocarbonyl)sulfanyl methylbenzoic acid, RAFT agent. To a stirring solution of 1,4 butanethiol (0.035 mol, 3.40 g), carbon disulfide (0.070 mol, 5.30 g) in chloroform (50 mL) was added triethylamine (0.116 mol, 11.74 g) dropwise. The solution became yellow and then orange on formation of triethylammonium trithiocarbonate salt. The solution was left to stir at room temperature for 2 hours and then 4-chloromethyl benzoic acid (0.029 mol, 5 g), also dissolved in chloroform (30 mL) was added dropwise. The solution was left to stir for 16 hours at room temperature. It was then washed 5 × with 0.1 M

HCl, the organic layers combined, dried with anhydrous MgSO4 and filtered. The solvent was then removed under vacuum and the remaining yellow RAFT agent, 4- (n-butylsulfanylthiocarbonyl)sulfanyl methylbenzoic acid, was collected by 1 filtration with hexane (7 g, 80%). H NMR (400 MHz, d6-acetone) : 0.92 (t, 3H, J

7.3 Hz, CH3), 1.39 - 1.49 (m, 2H, CH2), 1.66 - 1.73 (m, 2H, CH2), 3.44 (t, J 7.3 Hz,

2H, SCH2), 4.78 (s, 2H, ArCH2), 7.55 (d, J 8.4 Hz, 2H, ArH), 8.01 (d, J 8.4 Hz, 13 2H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 13.8, 22.6, 30.8, 37.3, 40.9, 130.2, 130.7, 130.7, 142.0, 167.2, 224.5 ppm.

241 Chapter 8. The Application of a Photochromic Probe... ______

Synthesis of 2-hydroxyethyl-4-(n-butylsulfanylthiocarbonyl)sulfanyl methyl benzoate, RAFT agent. To an ice-cooled solution of dried ethylene glycol (18.0 g, 0.290 mol) and triethylamine (6.1 mL, 4.43 g, 0.044 mol) in dry dichloromethane (30 mL) was added dropwise, 4-(chloromethyl)benzoyl chloride (5.5 g, 0.029 mol) under argon. The solution was stirred with ice cooling for half an hour and was then left to stir for an additional 12 hours at room temperature. The solution was washed with water 3 × and then brine. The organic layer was dried with anhydrous

MgSO4 and the solvent was evaporated under vacuum to give 2-hydroxyethyl 4- (chloromethyl)benzoate, a thick yellow oil that became a wax on standing (6.41 g). 1H NMR showed this intermediate product to be of sufficient purity for subsequent use. The same procedure as described above was followed for the synthesis of the corresponding triethylammonium trithiocarbonate salt in chloroform, using 1,4 butanethiol (0.038 mol, 3.45 g), carbon disulfide (0.071 mol, 5.36 g) and triethylamine (8.91 g, 0.0.088 mol). 2-Hydroxyethyl-4-(chloromethyl)benzoate (0.029 mol, 6.31 g), dissolved in chloroform was then added dropwise and the solution left to stir at room temperature for 16 hours. The chloroform was removed under vacuum and the residue dissolved in diethyl ether. It was then washed with water and dried with anhydrous MgSO4. The solvent was then removed under vacuum and the remaining yellow oil was purified by column chromatography (silica gel, diethyl ether/hexane, 3:1) to give the RAFT agent, 2-hydroxyethyl-4-(n- butylsulfanylthiocarbonyl)sulfanyl methylbenzoate, as a waxy yellow solid (3.3 g, 1 30%). H NMR (400 MHz, CDCl3) : 0.94 (t, 3H, J 7.3 Hz, CH3), 1.39 - 1.49 (m,

2H, CH2), 1.66 - 1.73 (m, 2H, CH2), 3.39 (t, J 7.3 Hz, 2H, SCH2), 4.67 (s, 2H, 13 ArCH2), 7.45 (d, J 7.7 Hz, 2H, ArH), 8.05 (d, J 7.3 Hz, 2H, ArH) ppm. C NMR

(100 MHz, d6-acetone) : 14.8, 23.6, 38.3; 41,8, 31.8, 61.7, 68.5, 131.2, 131.5, 131.6, 143.1, 167.4, 225.5 ppm.

242 Chapter 8. The Application of a Photochromic Probe... ______

Synthesis of, 9'-(4-((n-butylsulfanylthiocarbonyl)sulfanyl)methylbenzoyl)-1,3,3- trimethylspiroindoline-2,3'-3Hnaphtho2,1-b1,4oxazine, SOX-RAFT agent. 4-(n- butylsulfanylthiocarbonyl)sulfanyl methylbenzoic acid (2.0 g, ca. 6.66 mmol) was dissolved in dry CH2Cl2 (100 mL) under nitrogen and 1 small drop DMF added. To the mixture was added oxalyl chloride (1.52 g, 1.03 mL, 11.98 mmol) using a gas-tight syringe. The mixture was stirred at ambient temperature for 3 hours. The solvent and excess reagents were removed under vacuum with residual traces of oxalyl chloride removed with the aid of 1,2-dichloroethane. Analysis by 1H NMR showed quantitative conversion to the corresponding 4-(n- 1 butylsulfanylthiocarbonyl)sulfanylmethylbenzoyl chloride. H NMR (400 MHz, d6- acetone) : 0.92 (t, 3H, J 7.3 Hz, CH3), 1.38 - 1.47 (m, 2H, CH2), 1.65 - 1.72 (m,

2H, CH2), 3.42 (t, J 7.3 Hz, 2H, SCH2), 4.82 (s, 2H, ArCH2), 7.66 (d, J 8.42 Hz, 13 2H, ArH), 8.09 (d, J 8.42 Hz, 2H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 13.8, 22.6, 30.8, 37.5, 40.4, 130.9, 132.4, 132.8, 145.8, 168.1, 224.2 ppm. To an ice-cooled solution of 9'-hydroxy-1,3,3-trimethylspiroindoline-2,3'-3H- naphtho2,1-b1,4oxazine81 (2.09 g, 6.05 mmol) and triethylamine (1.35 g, 1.86 mL,

13.32 mmol) in dry CH2Cl2 (100 mL), was added dropwise the full quantity of 4-(n- butylsulfanylthiocarbonyl)sulfanylmethylbenzoyl chloride in dry CH2Cl2 (35 mL). The mixture was left to stir at room temperature overnight. The solvent was then removed under vacuum and the residue purified by column chromatography (silica gel, diethyl ether/hexane, 3:2) to give the title compound as mustard coloured solid (3.5 g, 92%).

243 Chapter 8. The Application of a Photochromic Probe... ______

1 H NMR (400 MHz, d6-acetone) : 0.94 (t, 3H, J 7.3 Hz, CH3), 1.35 (2 × overlapping s, 6H, 2 × CH3), 1.41 - 1.50 (m, 2H, CH2), 1.67 - 1.73 (m, 2H, CH2), 2.78 (s, 3H, N-

CH3), 3.46 (t, J 7.3 Hz, 2H, SCH2), 4.85 (s, 2H, ArCH2), 6.66 (d, J 8.4 Hz, 1H, ArH), 6.88 (t, J 7.3 Hz, 1H, ArH), 7.07 (d, 9.2 Hz, 1H, ArH), 7.15 - 7.21 (m, 2H, ArH), 7.37 (dd, J 2.6, 9.2 Hz, 1H, ArH), 7.68 (d, J 8.1 Hz, 2H, ArH), 7.83 - 7.87 (m, 2H, ArH), 7.95 (d, J 8.78 Hz, 1H, ArH), 8.22 (d, J 8.42 Hz, 2H, ArH), 8.40 (app d, J 2.2 Hz, 1H, 13 ArH) ppm. C NMR (100 MHz, C6D6) : 13.6, 20.7, 22.2, 25.2, 29.4, 30.2, 37.0, 40.8, 51.8, 99.1, 107.5, 113.9, 116.6, 120.1, 120.3, 121.6, 123.7, 129.5, 129.6, 129.6, 129.7, 130.3, 130.3, 130.8, 132.7, 136.2, 141.5, 145.1, 148.0, 150.8, 150.9, 164.8, 223.3 ppm.

Synthesis of 9'-acrylyloxy-1,3,3-trimethylspiroindoline-2,3'-3Hnaphtho2,1- b1,4oxazine, (SOX-ACR). The title compound was synthesized as SOX-RAFT agent above, however using 9'-hydroxy-1,3,3-trimethylspiroindoline-2,3'- 3Hnaphtho2,1-b1,4oxazine81 (1.51 g, 4.38 mmol), acryloyl chloride (0.44 g, 4.83 mmol) and triethylamine (0.67 g, 6.57 mmol) in dry CH2Cl2 (40 mL). The reaction mixture was stirred for 2 hours in total and the product obtained as a pale cream solid (1.60 g, 92%) after purification by column chromatography (silica gel, 1 CH2Cl2). H NMR (400 MHz, d6-acetone) : 1.34 (s, 3H, CH3), 1.36 (s, 3H, CH3),

2.78 (s, 3H, N-CH3), 6.14 (dd, J 10.55 Hz, J 1.46 Hz, 1H, =CH), 6.46 (dd, J 17.20 Hz, J 10.25 Hz, 1H, =CH), 6.60 -6.67 (m, 2H, =CH and ArH), 6.85 - 6.89 (m, 1H, ArH), 7.05 (d, J 8.78 Hz, 1H, ArH), 7.14 - 7.21 (m, 2H, ArH), 7.25 (dd, J 2.6, J 8.78 Hz, 1H, ArH), 7.82 - 7.84 (m, 2H, ArH), 7.90 (d, J 8.78 Hz, 1H, ArH), 8.29 13 (d, J 2.60 Hz, 1H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 21.9; 26.7; 30.7; 53.5; 100.7; 109.0; 114.5; 118.3; 123.2; 121.6; 121.3; 124.8; 129.2; 129.9; 129.7; 131.9; 131.3; 134.1; 133.6; 137.7; 146.6; 149.5; 151.7; 153.1; 166.0 ppm.

244 Chapter 8. The Application of a Photochromic Probe... ______

Synthesis of 9'-propionyloxy-1,3,3-trimethylspiroindoline-2,3'-3Hnaphtho2,1- b1,4oxazine, (SOX-PROP). The title compound was synthesized using the same procedure as SOX-ACR, however using 9'-hydroxy-1,3,3-trimethylspiroindoline- 2,3'-3Hnaphtho2,1-b1,4oxazine81 (0.20 g, 0.58 mmol), propionyl chloride (0.054 g,

0.58 mmol) and triethylamine (0.106 g, 1.74 mmol) in dry CH2Cl2 (5 mL). The reaction mixture was stirred for 30 minutes in total and the product obtained as a pale cream solid (0.20 g, 86%) after purification by column chromatography (silica 1 gel, diethyl ether/hexane, 1:1). H NMR (400 MHz, d6-acetone) : 1.26 (t, J 7.56

Hz, 3H, CH3), 1.33 (s, 3H, CH3), 1.35 (s, 3H, CH3), 2.70 (q, J 7.55 Hz, 2H, CH2),

2.76 (s, 3H, N-CH3), 6.65 (d, J 7.72 Hz, 1H, ArH), 6.83 - 6.91 (m, 1H, ArH), 7.03 (d, J 8.87 Hz, 1H, ArH), 7.13 - 7.23 (m, 3H, ArH), 7.77 - 7.89 (m, 3H, ArH), 8.26 13 (d, J 2.37 Hz, 1H, ArH) ppm. C NMR (100 MHz, d6-acetone) : 9.1, 20.7, 25.5, 27.8, 29.5, 52.3, 99.5, 107.8, 113.4, 116.7, 120.3, 120.4, 122.1, 123.5, 127.9, 128.6, 129.9, 130.7, 132.4, 136.5, 145.4, 148.3, 150.8, 151.8, 173.1 ppm.

Synthesis of SOX-p(NIPAM)220-b-p(NAM)87 block copolymer 1. A solution of N- isopropyl acrylamide (NIPAM) (4.92g, 43.5 mmol), AIBN (azobisisobutyronitrile) (1.43mg, 8.71 × 10-6 mol) and SOX-RAFT agent (109 mg, 0.174 mmol) was prepared in 1,4-dioxane (25 mL). The final ratio of monomer to RAFT agent was 250:1 with 0.02 mol% of AIBN with respect to monomer. The mixture was divided between several ampoules which were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for up to 16 hours. Conversions were evaluated by 1H nmr by comparing the integration of the vinyl proton from the monomer at 6.6 ppm to the polymeric and monomer signals at 4 ppm from (CH3)2CH. The final polymers were purified precipitation into diethyl ether 2 × and vacuum drying till constant weight. Polymerization result for p(NIPAM) macro RAFT agent: time 16 hours; conversion = 88 %; Mn 35,050 1 g/mol, PDI 1.10 (GPC-DMF); Mn 25,490 g/mol ( H NMR estimate); Mn 25,520 g/mol (theoretical Mn).

245 Chapter 8. The Application of a Photochromic Probe... ______

The macro RAFT agent was used for subsequent block extension with N-acryloyl morpholine (NAM): A solution of NAM (0.41 g, 2.88 mmol), the p(NIPAM) macro RAFT agent (0.80 g, 3.14 × 10-5 mol), AIBN (0.25 mg, 1.52 × 10-6 mol) was prepared and transferred to an ampoule using 1,4-dioxane (ca. 2.5 mL). The final ratio of monomer to RAFT agent was 92:1 with 0.05 mol% of AIBN with respect to monomer. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 16 hours. The final conversion was evaluated gravimetrically on a small sample after removal of monomer and solvent and drying, in a vacuum oven until constant weight.

Polymerization result for SOX-p(NIPAM)220-b-p(NAM)87 1: time 16 hours; 1 conversion = 90%; Mn 47,470 g/mol, PDI 1.16 (GPC-DMF); Mn 38,360 g/mol ( H

NMR estimate); Mn 37,800 g/mol (theoretical Mn). GPC plots showing sequential block formation of the copolymer are displayed in Appendix 6.

Synthesis of p(NIPAM)243-co-p(SOX)1.2-b-p(NAM)92 block copolymer 2. A solution of NAM (2.45g, 17.4 mmol), AIBN (2.70 mg, 1.74 × 10-5 mol) and RAFT agent 5 (55 mg, 0.183 mmol) was completely transferred to an ampoule using 1,4- dioxane (ca. 10 mL). The final ratio of monomer to RAFT agent was 95:1 with 0.1 mol% of AIBN with respect to monomer. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 4 hours and 30 minutes. The final conversion was evaluated gravimetrically on a small sample after removal of monomer and solvent and drying, in a vacuum oven until constant weight. For GPC evaluation, a small sample of the polymer was modified by methylation of the carboxylic acid end- group with trimethylsilyldiazomethane, using a procedure reported in literature (Couvreur L. et al, Macromolecules, 2003, 36 (22), p8261). Polymerization result for p(NAM) macro RAFT agent: conversion = 95%; Mn 15,600 g/mol, PDI 1.03

246 Chapter 8. The Application of a Photochromic Probe... ______

1 (GPC-DMF); Mn 13,300 g/mol ( H NMR estimate); Mn 13,040 g/mol (theoretical

Mn). The p(NAM) macro RAFT agent was used for subsequent block extension with NIPAM and SOX-ACR: A solution of NIPAM (1.45 g, 12.77 mmol), SOX-AC (51.4 mg, 0.129 mmol), the p(NAM) macro RAFT agent (0.687 g, 5.17 × 10-5 mol) and AIBN (2.12 mg, 1.29 × 10-5 mol) was prepared and transferred to an ampoule using 1,4-dioxane (ca. 5 mL). The final ratio of monomers to RAFT agent was 250:1 with 0.1 mol% of AIBN with respect to monomers. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 16 hours. The conversions of NIPAM to polymer was evaluated by 1H nmr by comparing the integration of the vinyl proton from the monomer at 6.6 ppm to the polymeric and monomer signals at 4 ppm from

(CH3)2CH. The SOX-ACR appeared to be fully consumed. The final polymers were purified precipitation into diethyl ether 2 × and vacuum drying till constant weight. For GPC evaluation, a small sample of the polymer was modified by methylation as described above. Polymerization result for p(NIPAM)243-co- p(SOX)1.2-b-p(NAM)92 2: conversion = 95%; Mn 57,790 g/mol, PDI 1.16 (GPC- 1 DMF); Mn 41,300 g/mol ( H NMR estimate); Mn 40,180 g/mol (theoretical Mn).. GPC plots showing sequential block formation of the copolymer are displayed in Appendix 6.

Synthesis of p(NIPAM)115-co-p(SOX)1.3-b-p(NAM)93, 3 and p(NIPAM)178-co- p(SOX)1.6-b-p(NAM)93, 4 block copolymers. A solution of NAM (6.20 g, 43.9 mmol), AIBN (7.14 mg, 4.35 × 10-5 mol) and 2-hydroxyethyl-4-(n- butylsulfanylthiocarbonyl)sulfanyl methyl benzoate (158 mg, 0.458 mmol) was completely transferred to an ampoule using 1,4-dioxane (ca. 25 mL). The final

247 Chapter 8. The Application of a Photochromic Probe... ______ratio of monomer to RAFT agent was 96:1 with 0.1 mol% of AIBN with respect to monomer. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 3 hours. The final conversion was evaluated gravimetrically on a small sample after removal of monomer and solvent and drying in a vacuum oven until constant weight.

Polymerization result for p(NAM) macro RAFT agent: conversion = 97%; Mn 1 13,300 g/mol, PDI 1.05 (GPC-DMF); Mn 13,600 g/mol ( H NMR estimate); Mn

13,150 g/mol (theoretical Mn). The macro RAFT agent was used for subsequent block extension with NIPAM and SOX-ACR: A solution of NIPAM (2.06 g, 14.59 mmol), SOX-ACR (74.0 mg, 0.129 mmol), the aforementioned p(NAM) macro RAFT agent (1.05 g, 7.72 × 10-5 mol) and AIBN (3.0 mg, 1.83 × 10-5 mol) was prepared using 1,4-dioxane (ca. 8.5 mL) and split into two ampoules. The final ratio of monomers to RAFT agent in each was 250:1 with 0.1 mol% of AIBN with respect to monomers. The ampoules were then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 50 minutes and 2 hours. The conversions of NIPAM to polymer was evaluated by 1H nmr by comparing the integration of the vinyl proton from the monomer at 6.6 ppm to the polymeric and monomer signals at 4 ppm from

(CH3)2CH. The SOX-ACR appeared to be fully consumed. The final polymers were purified precipitation into diethyl ether 2 × and vacuum drying until constant weight was achieved.

Polymerization result for p(NIPAM)115-co-p(SOX)1.3-b-p(NAM)93, 3: time = 50 minutes, conversion = 55%; Mn 27,200 g/mol, PDI 1.16 (GPC-DMF); Mn 26,800 1 g/mol ( H NMR estimate); Mn 29,160 g/mol (theoretical Mn).

Polymerization result for p(NIPAM)178-co-p(SOX)1.6-b-p(NAM)93, 4: time = 2 hours, conversion = 72%; Mn 35,350 g/mol, PDI 1.22 (GPC-DMF); Mn 34,080 1 g/mol ( H NMR estimate); Mn 33,970 g/mol (theoretical Mn)GPC plots showing sequential block formation of the copolymers are displayed in Appendix 6.

248 Chapter 8. The Application of a Photochromic Probe... ______

Synthesis of p(BA)89-b-(NAM)93 block copolymer 5. Block copolymer 5 was synthesised by the extension of the same p(NAM) macro RAFT agent as used above. A solution of n-butyl acrylate (n-BA) (1.41 g, 11.0 mmol), the aforementioned p(NAM) macro RAFT agent (1.0 g, 7.35 × 10-5 mol) and AIBN (1.5 mg, 9.10 × 10-6 mol) was transferred into an ampoule using 1,4-dioxane (ca. 2 mL). It was then degassed with three freeze-pump-thaw cycles, sealed and heated at 60 °C in a thermostatted oil bath for 6 hours. The final ratio of monomers to RAFT agent was 150:1 with 0.08 mol% of AIBN with respect to monomer. The conversion was evaluated by 1H nmr. The resonances integrated to obtain conversions were the vinyl peaks at 5.8, 6.2 and 6.4 ppm (monomer only) and the OCH2- peaks at 3.9 - 4.1 ppm (monomer and polymer). The polymer was then purified by evaporation of excess monomer over a gentle stream of N2, dissolution of the crude mixtures into CH2Cl2, precipitation into methanol and decanting the supernatant liquid. Precipitation was carried out 2 × and the polymer was then dried in a vacuum oven for 48 hours.

Polymerization result for p(BA)89-b-p(NAM)93 5: conversion = 64%; Mn 21,328 1 g/mol, PDI 1.20 (GPC-DMF); Mn 24,881 g/mol ( H NMR estimate); Mn 25,900 g/mol

(theoretical Mn). GPC plots showing sequential block formation of the copolymer are displayed in Appendix 6.

Synthesis of SOX-p(BA)135-b-p(NAM)104 block copolymer 6. A solution of n-BA (7.05 g, 55.0 mmol), AIBN (3mg, 1.84 ×10-5 mol) and SOX-RAFT agent (230 mg, 0.367 mmol) was prepared in benzene (10 mL). The final ratio of monomer to RAFT agent was 150:1 with 0.03 mol% of AIBN with respect to monomer. The

249 Chapter 8. The Application of a Photochromic Probe... ______mixture was transferred to an ampoule which was then degassed with three freeze- pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 8 hours. The conversion was evaluated by 1H nmr. The resonances integrated were the vinyl peaks at 5.8, 6.2 and 6.4 ppm (monomer only) and the OCH2- peaks at 3.9 - 4.1 ppm (monomer and polymer). The polymer was then purified by evaporation of excess monomer over a gentle stream of N2, dissolution of the crude mixtures into CH2Cl2, precipitation into methanol and decanting the supernatant liquid. Precipitation was carried out 2 × and the polymer then dried in a vacuum oven for 48 hours. Polymerization result for p(BA) macro RAFT agent: conversion = 84%; 1 Mn 20,430 g/mol, PDI 1.04 (GPC-DMF); Mn 17,980 g/mol ( H NMR estimate); Mn

16,790 g/mol (theoretical Mn). The p(BA) macro RAFT agent was used for subsequent block extension with NAM: A solution of NAM (1.20g, 8.50 mmol), the aforementioned p(BA) macro RAFT agent (1.30g, 7.23 × 10-5 mol) and AIBN (0.64 mg, 3.90 × 10-6 mol) was prepared and transferred to an ampoule using 1,4-dioxane (ca. 6 mL). The final ratio of monomer to RAFT agent was 118:1 with 0.05 mol% of AIBN with respect to monomer. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 16 hours. The polymer was then purified by dissolution of the crude mixtures into CH2Cl2, precipitation into methanol and decanting the supernatant liquid. Precipitation was carried out 2 × and the polymer was then dried in a vacuum oven for 48 hours. The final conversion was evaluated gravimetrically on a small sample after removal of monomer and solvent and drying, in a vacuum oven until constant weight.

Polymerization result for SOX-p(BA)135-b-p(NAM)104 block copolymer 6: 1 conversion = 85%; Mn 35,680 g/mol, PDI 1.06 (GPC-DMF); Mn 32,690 g/mol ( H

NMR estimate); Mn 32,140 g/mol (theoretical Mn). GPC plots showing sequential block formation of the copolymer are displayed in Appendix 6.

Synthesis of control polymer SOX-p(NAM)84. A solution of NAM (1.46 g, 10.3 mmol), AIBN (1.4 mg, 8.84 × 10-6 mol) and SOX-RAFT agent (68 mg, 0.109 mmol)

250 Chapter 8. The Application of a Photochromic Probe... ______was transferred to an ampoule using 1,4-dioxane (ca. 5 mL). The final ratio of monomer to RAFT agent was 95:1 with 0.09 mol% of AIBN with respect to monomer. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 16 hours. The final conversion was evaluated gravimetrically on a small sample after removal of monomer and solvent and drying, in a vacuum oven until constant weight. Polymerization result for

SOX-p(NAM)84: conversion = 90%; Mn 14,300 g/mol, PDI 1.04 (GPC-DMF); Mn 1 12,450 ( H NMR estimate); Mn 11,360 g/mol (theoretical Mn).

Synthesis of control polymer p(SOX)1-co-p(NAM)93. A solution of NAM (2.43g, 17.2 mmol), SOX-ACR (69 mg, 0.174 mmol), AIBN (2.90 mg, 1.74 × 10-5 mol) and 4-(n-butylsulfanylthiocarbonyl)sulfanyl methylbenzoic acid RAFT agent (55 mg, 0.183 mmol) was transferred to an ampoule using 1,4-dioxane (ca.10 mL). The final ratio of monomers to RAFT agent was 95:1 with 0.1 mol% of AIBN with respect to monomer. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 4 hours and 30 minutes. The final conversion was evaluated gravimetrically on a small sample after removal of monomer and solvent and drying, in a vacuum oven until constant weight. For GPC evaluation, a small sample of the polymer was modified by methylation of the carboxylic acid end-group with trimethylsilyldiazomethane, using a procedure reported in literature (Couvreur L. et al, Macromolecules, 2003,

36 (22), p8261). Polymerization result for p(SOX)1-co-p(NAM)93 polymer: 1 conversion = 98%; Mn 20,132 g/mol, PDI 1.03 (GPC-DMF); Mn 13,900 g/mol ( H

NMR estimate); Mn 13,440 g/mol (theoretical Mn).

251 Chapter 8. The Application of a Photochromic Probe... ______

Synthesis of Control polymer p(SOX)1.1-co-p(NAM)93. A solution of NAM (1.22 g, 8.64 mmol), SOX-ACR (34.7 mg, 8.71 × 10-5 mmol), AIBN (1.43 mg, 0.871 × 10-5 mol) and 2-hydroxyethyl-4-(n-butylsulfanylthiocarbonyl)sulfanyl methyl benzoate RAFT agent (32.3 mg, 9.38 × 10-5 mol) was transferred to an ampoule using 1,4- dioxane (ca. 5 mL). The final ratio of monomer to RAFT agent was 93:1 with 0.1 mol% of AIBN with respect to monomers. The ampoule was then degassed with three freeze-pump-thaw cycles, sealed and then heated at 60 °C in a thermostatted oil bath for 4 hours. The final conversion was evaluated gravimetrically on a small sample after removal of monomer and solvent and drying, in a vacuum oven until constant weight. Polymerization result for p(SOX)1.1-co-p(NAM)93: conversion = 95%; Mn 1 12,930 g/mol, PDI 1.05 (GPC-DMF); Mn 13,600 g/mol ( H NMR estimate); Mn

12,700 g/mol (theoretical Mn).

8.5 References

(1). Boyer, C.; Bulmus, V.; Davis, T. P.; Ladmiral, V.; Liu, J. Q.; Perrier, S. Chem. Rev. 2009, 109, 5402-5436. (2). Blanazs, S. P.; Armes S. P.; Ryan J. Macromol. Rapid Commun. 2009, 30, 267- 277. (3). Stenzel M. H. Chem. Comm., 2008, 3486-3503. (4). Wu C.; Zhou S. Macromolecules, 1995, 28, 8381-8387. (5). Wu C.; Zhou S. Macromolecules, 1995, 28, 5388-5390. (6). Kujawa P.; Aseyev V.; Tenhu H.; Winnik F. M. Macromolecules, 2006, 39, 7686-7693. (7). Shibayama, M.; Tanaka, T. Adv. Polym. Sci. 1993, 109, 1-62. (8). Plummer, R.; Hill, D. J. T.; Whittaker, A. K. Macromolecules 2006, 39, 8379- 8388.

252 Chapter 8. The Application of a Photochromic Probe... ______

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253 Chapter 8. The Application of a Photochromic Probe... ______

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256 9 General Conclusions

The research work presented in this thesis has focused on the application and control of photochromism through the intimate interaction of dyes with polymers. Novel photochromic-polymer conjugates were investigated with the goal of improving their general understanding and application, extending existing methodologies and applying new concepts to control photochromic behaviour. The research was carried out chapter by chapter and each can stand independently as separate works. In an otherwise rigid lens matrix, which can severely restrict dye mobility, an improved and favourable local environment for switching can be provided for a photochromic dye by having one or more polymer tails attached to it. Polymer conjugation can be applied to the dye by using controlled polymerization techniques such as ATRP, by either growing polymer tail/s from a photochromic-fucntionalized initiator or by growing a polymer chain using a photochromic-functionalized monomer. Chapters 3 and 4 applied this general concept, as summarized below. Chapter 3 was a comprehensive examination which confirmed that the described polymer conjugation strategy is both practical and applicable to naphthopyrans for controlling their fade kinetics in a lens matrix. Furthermore it showed that this could be achieved systematically within a broad range. Changing the nature of the polymer tail allows the dye’s local rigidity within the host matrix to be altered and this provides a means to broadly tune the decolouration kinetics. Systematic tuning is achieved by the chain length modification of the end-functionalized conjugates, which are efficiently made from a naphthopyran-functionalized ATRP initiator. Enhanced colouration was found to be a concurrent effect to an increase in switching speed. Naphthopyran copolymer comparisons made using dye-functionalized monomers displayed pronounced photochromic responses. This last result is evidence that a stronger influence is provided from the conjugated polymer tail when the dye is pendant along the polymer backbone, as opposed to being directly located at the end. This aspect was considered in the next chapter. In Chapter 4 ATRP was also used to synthesize naphthopyran-polymer conjugates, however this time it was with a view to examining a variety of architectures. I showed that regardless of the method used to assemble a photochromic material, such as casting in a lens host matrix or making a film composed entirely of the photochromic-polymer conjugate, the ability to manipulate polymer architecture provides an extra avenue to Chapter 9. Conclusions ______

control photochromic properties, beyond chain length and rigidity (Tg). Firstly, the photochromic kinetics of the conjugates were investigated within a lens rigid matrix. An investigation of various p(n-BA) homopolymers showed that mid-functional placement of the dye, made possible using di-functional photochromic initiators, gave superior kinetics per chain length of conjugated polymer. However, having the dye pendant from the middle of the chain was found to be an advantage, compared to having it directly within the middle of the polymer backbone. Analysis of naphthopyran-p(n-BA) copolymers showed that having the dye pendant from the chain as a monomer unit was also attractive; however, the ability to tune response via chain length was not achieved using this strategy. A better approach was a gradient copolymer system made with a non-photochromic di-functional initiator that allowed total incorporation of the naphthopyran monomer (a methacrylate) in the middle section of the polymer chains. In the second part, the formation of copolymers with the photochromic encapsulated in the middle of a Y-branched central soft section was made possible using ABA triblock geometry. The described films showed enhanced tuning ability of their responses which was dependent on the overall proportion of soft section inhabited by the photochromic. In Chapter 5 I demonstrated an alternative method which is the conjuation of a preformed polymer onto the dye, in this case, commercially available poly(dimethylsiloxane) (PDMS). Efficient routes that were used to access the relavent starting materials to form the necessary hydroxyl functionalized naphthopyrans were discussed. The subsequent conjugation strategy was also presented as part of the investigation. The ability to make conjugatable hydroxyl forms of the dyes is an important step for the commercial application of the technology. The attachment of PDMS to various methoxy substituted naphthopyrans was found to give markedly superior photochromic performance in colouration and decolouration speeds and, for a majority of the samples tested, greater colourabilties were also achieved within a rigid host matrix. The aforementioned technologies therefore remain a competitive alternative for tuning fade kinetics compared to modifying the electronic structure of the dye or their host matrix. In Chapter 6 various naphthopyran monomers were reacted with the polymerizable lens composition to become part of the final crosslinked network structure and their photochromic behaviour was subsequently investigated. Matrix tethering may be advantageous in terms of preventing migration and blooming of photochromic-polymer

258 Chapter 9. Conclusions ______conjugates in the lens material over time. The study was also used to uncover some of the critical factors that effect colouration and decolouration behaviour when bound within the network structure of a lens. Tethering to the rigid matrix was found to restrict the ability of the dye to move and universally caused a decrease in colouration and decolouration rates, compared to unbound dyes. Tethering by two reactive points located on opposite sides of the dye molecule also caused a further reduction in switching speed, resulting in very low levels of colouration. The fade kinetics displayed by matrix tethered dyes was also found to be more complex indicating that their local environment is less homogenous overall. By using a PEG spacer to separate the tethering point from the dye, fade kinetics were made to approach those of un-tethered controls. An EG-succinate spacer was found to have the largest impact by directly separating the tethering point/s from the dye itself. The distance of the dye from the tethering point was found to be less important for longer spacers. Another factor that was also found to influence both fade kinetics and colourability in an unexpected manner was whether the tethering point was attached to the top or bottom section of the molecule. This factor was clarified in the next chapter by measuring the solution kinetics of linear polymers formed from the two monomers. This showed that a higher level of incorporation of one of the monomers in to the network structure is the most likely factor accounting for differences in kinetics in the matrix. In Chapter 7 I explored hyperbranched polymer structures which also incorporated bound photochromic units as part of the bulk matrices, either as single-bound pendant groups or bis-reacted crosslinking agents. The slower kinetics displayed by the hyperbranched films (pMMA and pMA), incorporating bis-tethered photochromic units, as compared to the kinetics displayed by the analogous network structure (7 in Chapter 6) indicated that the length of the crosslinking agents are an important factor influencing overall kinetics. Longer and more flexible units in the hyperbranched polymers are expected to provide a less dense environment which is suitable for faster switching. An extensive comparative study could also make use of the photochromic dyes as probe molecules for exploring different polymeric environments. Finally in Chapter 8 I showed that the strong sensitivity of photochromic dyes to their surroundings can be applied to probe their local environment. In this study this approach was used to monitor the formation of micelles since the aggregation of polymer sections during their assembly leads to measurable changes in the dye’s environment and therefore behaviour. This aspect could be further exploited in other

259 Chapter 9. Conclusions ______materials to investigate other nano-scale interactions and dynamic behaviours. The compatibility of the hydrophilic conjugates with aqueous media also makes them interesting candidates for probing biochemical processes in aqueous media.

A substantial portion of the research work presented in this thesis has been devoted to the chemical synthesis of the dye derivatives. This is not surprising given that photochromism finds its roots in chemistry. Our experiences with naphthopyran dyes are that they require an appropriate level of attention to organic chemistry. Such persistence has meant that our research group now has the expertise of synthesizing commercially available dyes in a conjugatable (hydroxyl) form and this is what ultimately allows them to be transformed into an array of polymer conjugates. This thesis work has certainly benefitted from such efforts. Undoubtedly, the ability to exploit controlled radical polymerisation techniques to synthesize engineered polymers as novel macromolecular constructs has led to new developments in material science and nanotechnologies. As exemplified in this thesis, it has opened up new possibilities to apply, understand and develop photochromic materials. Ongoing improvements in the design of photo-responsive systems, especially those which allow photochromics to be intuitively located within specialized environments, will continue to open up new opportunities for photochromic polymers.

260 Acknowledgements

The majority of the synthesis work devoted to this thesis was conducted at CSIRO, Molecular and Health Technologies, now and Engineering Division. The photochromic testing was conducted at CAMD (Centre for Advanced Molecular Design) at the University of NSW, a fantastic research group that accepted me as a postgraduate student in 2007. The Cooperative Research Centre (CRC) for Polymers financially supported my research work in the form of a scholarship which enabled me to use the facilities, equipment and chemicals at CSIRO and also allowed me to travel regularly between CSIRO and UNSW. I gratefully acknowledge their support, in particular, Ian Dagley, Steve Wright and all the administrative staff. I would like to thank my supervisor at CAMD, Tom Davis, for his welcoming and positive nature and belief in me. Your intelligence and sharp insight were greatly appreciated, especially during my limited visits. To my main supervisor, Richard Evans, a big thank-you. I acknowledge that I am not the easiest person to supervise but you did a great job by encouraging me to write papers and patting me on my back when I doubted myself. It was great being able to hear your thoughts in the lab on so many topics which always brought a smile to my face. Your passion for science, especially chemistry, is infectious. The indeno-fused photochromic derivatives in Chapter 5 were synthesized by Dr Nino Malic. His input and contribution to the work is gratefully acknowledged. Nino, I was so blessed to have you around during my PhD, on so many levels. You have been like a supervisor to me during many stages of my PhD, sharing your knowledge of organic synthesis and matters regarding photochromics. I have learnt so much from you and I will take that to my next job. Thankyou also for your on going friendship and understanding. Simon Harrisson, you have also been a gem. I was so lucky to have you close, for advice, to learn and to bounce around ideas. Your enthusiasm for science and incredible mind is an asset to everyone that knows you. You have also taught me so much and I hope to one day have the chance to work with you again. Thanks also for your on going friendship. I would also like to say a big thankyou to my fellow lab mates here at CSIRO: Quoxin Li, Daniel Keddie and Subashni Nisha, thankyou for your patience in the lab and Acknowledgements ______putting up with my grumpy moods and outbursts so graciously. Thanks for your support and fun times in the lab together. To my other friends here at CSIRO, some who have moved to greener pastures: Ben Muir, Thomas Ameringer, Glenn Condie, Warren Knower, Pete Cass, Richard Williams, Suzi Parera, Peter Harbour, Paul Pasic, Melissa Skidmore, Florian Greichen and Mike O’Shea. You guys have been a great support network. Thanks also for the fun times outside of work and the advice and chats during breaks To my fellow female science buddies, Glenna Drisko and Cara Doherty. Thanks for all the chats and whinge sessions and for your amazing support. Georgie Such, thanks for your encouragement and giving me the courage to start a PhD. To my friends here and overseas, Massimo Benaglia, Fiona Lee, Yannick Lorvo, Andy and Beth. It was great meeting up during the two overseas trips during my PhD. A big thankyou to Jonathan Campbell for looking after the photochromic testing rig so well at CAMD and helping me out if I had a problem with it. I am very grateful that you always had time for me. The instrumentation staff at CSIRO: Roger Mulder and Jo Cosgriff (NMR); Carl Braybrook (Mass Spec) and Mike Devery. At CAMD I would like to thank Mikey Whittaker. Thanks for mentoring me, the friendship, your support during my dark times and for being critical during by brighter moments. Rohan Holmes, Jatin Kumar and Anthony Granville, thanks for your support and company when I visited CAMD and the fun times we have had together at conferences. Thankyou Steve (Istvan) Jacenyick and Ik Ling for your administrative support at UNSW. Thankyou also to the academics at CAMD who made me feel welcome and accepted. To my in-laws overseas, a big thank-you for all your support and hospitality when I have visited. Your kindness is always appreciated. Sheridan, your words of wisdom have given me a lot of strength over the years, thankyou for taking the time to listen to me and making me feel special. To my family, a massive thankyou also: Dad, Mum, Silvia, Sergio, Miriam, Cosimo, Justin, Paula, Maya, Adam, Casper, Leonardo, Luca, Nelson, Maya and Ilija. Words cannot express my gratitude for your support and patience. Your positive attitude and belief in me gave me lots of strength. Lastly, to my wonderful partner Almar Postma. I could not have done this without you. Thankyou for your patience, guidance and encouragement. Thankyou for putting things

262 Acknowledgements ______into perspective and reminding me to look after myself. And thankyou also for reminding me that there is a life outside of work that needs to be nourished from time to time…so true!

263 Appendix 1. Supplementary Material for Chapter 3 ______

Appendix 1. Supplementary Material for Chapter 3 Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation.

2.5

2

1.5 /[M]) 0

1 ln([M]

0.5

0 0 100 200 300 400 500 600 700 800 900 1000 time / min

Figure 1. Pseudo-first order rate plot for the polymerization of methyl methacrylate with 3 at 90 C in toluene, [monomer]/[CuBr]/[N-(n-pentyl)-2-pyridylmethanimine]/[3] = 200:1:2:1.

1.2

1.0

0.8 /[M]) 0 0.6 ln([M] 0.4

0.2

0.0 100 150 200 250 300 350 400 time / min

Figure 2. Pseudo-first order rate plot for the polymerization of 2-(9H-carbazol-9- yl)ethyl methacrylate with 3 at 90 °C in toluene where [monomer]/[CuBr]/[N-(n- pentyl)-2-pyridylmethanimine]/[3] = 100:1:2:1, showing a distinct change of polymerization rate at 5 hours.

A1 Appendix 1. Supplementary Material for Chapter 3 ______

1.4

1.2

1

0.8 /[M]) 0

0.6 ln ([M] ln

0.4

0.2

0 0 100 200 300 400 500 time / min

Figure 3. Pseudo-first order rate plot for the polymerization of 3 with 2-(ethylhexyl acrylate) 90 °C in bulk where [monomer]/[CuBr]/[4,4’dinonyl-2,2’-bipyridine]/[3] = 150:1:2:1.

A2 Appendix 1. Supplementary Material for Chapter 3 ______

Figure 4. 1H NMR spectrum (d6-acetone) of poly(methyl methacrylate)-naphthopyran end-functional conjugate 7a with peak assignments.

Figure 5. 1H NMR spectrum (d6-acetone) of poly(methyl methacrylate)-naphthopyran copolymer 9 with peak assignments.

A3 Appendix 1. Supplementary Material for Chapter 3 ______

1 Figure 6. H NMR spectrum (CDCl3) of poly(carbazolylethyl methacrylate)- naphthopyran end-functional conjugate 8d with peak assignments.

1 Figure 7. H NMR spectrum (CDCl3) of poly(carbazolylethyl methacrylate) naphthopyran copolymer 10 with peak assignments.

A4 Appendix 1. Supplementary Material for Chapter 3 ______

Figure 8. 1H NMR spectrum (d6-acetone) of poly(2-(ethylhexyl acrylate) naphthopyran end-functional conjugate 6b with peak assignments.

1 Figure 9. H NMR spectrum (d6-acetone) of poly(2-(ethylhexyl acrylate) naphthopyran copolymer 11 with peak assignments.

A5 Appendix 2. Supplementary Material for Chapter 4 ______

Appendix 2. Supplementary Material for Chapter 4 Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix.

1.2

1.0

0.8 /[M]) 0 0.6 ln([M] 0.4

0.2

0.0 0 200 400 600 800 Time (mins)

Figure 1. Pseudo-first order rate plot for the: () Atom Transfer Radical Copolymerization of n-butyl acrylate (98 %) with monomer 11 (2 %) at 90 °C in benzene with [monomers]/[CuBr]/[4,4'dinonyl-2,2'-bipyridine]/[ethyl-2- bromoisobutyrate initiator] = 150:1:2:1; () Atom Transfer Radical Polymerization of n-butyl acrylate with initiator 7 at 90 °C in benzene with [monomer]/[CuBr]/[4,4'dinonyl-2,2'-bipyridine]/[7] = 200:1:2:1; () Atom Transfer Radical Polymerization of n-butyl acrylate with initiator 5 at 90 °C in benzene with [monomer]/[CuBr]/[4,4'dinonyl-2,2'-bipyridine]/[5] = 100:1:2:1; () Atom Transfer Radical Polymerization of n-butyl acrylate with initiator 6 at 90 °C in benzene where [monomer]/[CuBr]/[4,4'dinonyl-2,2'-bipyridine]/[6] = 200:1:2:1.

A6 Appendix 2. Supplementary Material for Chapter 4 ______

1 Figure 2. H NMR spectrum (d6-acetone) of naphthopyran ATRP initiator 5 with peak assignments.

1 Figure 3. H NMR spectrum (d6-acetone) of poly(n-butyl acrylate)-naphthopyran end- functional conjugate 8b with peak assignments.

A7 Appendix 2. Supplementary Material for Chapter 4 ______

1 Figure 4. H NMR spectrum (d6-acetone) of naphthopyran ATRP initiator 7 with peak assignments.

1 Figure 5. H NMR spectrum (d6-acetone) of poly(n-butyl acrylate)-naphthopyran mid- functional conjugate 10b with peak assignments.

A8 Appendix 2. Supplementary Material for Chapter 4 ______

1 Figure 6. H NMR spectrum (d6-acetone) of naphthopyran ATRP initiator 6 with peak assignments.

1 Figure 7. H NMR spectrum (d6-acetone) of poly(n-butyl acrylate)-naphthopyran Y- branched and mid-functional conjugate 9b with peak assignments.

A9 Appendix 2. Supplementary Material for Chapter 4 ______

1 Figure 8. H NMR spectrum (d6-acetone) of poly(n-butyl acrylate)-naphthopyran copolymer 13a with peak assignments.

1 Figure 9. H NMR spectrum (d6-acetone) of Y-branched poly(n-butyl acrylate) naphthopyran copolymer 14a with peak assignments.

A10 Appendix 2. Supplementary Material for Chapter 4 ______

1 Figure 10. H NMR spectrum (CDCl3) of naphthopyran mid-functional ABA triblock copolymer 15b with peak assignments.

A11 Appendix 2. Supplementary Material for Chapter 4 ______

8e 8d 8c 8b 8a 1 Normalized GPC Intensity 0 25 27 29 31 33 35 37 Retention Time (mins)

Figure 11. Overlaid and normalized GPC traces of poly(n-butyl acrylate)-naphthopyran end-functional conjugates 8a-8e.

9e 9d 9c 9b 9a 1 Normalized GPC Intensity 0 25 27 29 31 33 35 37 Retention Time (mins)

Figure 12. Overlaid and normalized GPC traces of poly(n-butyl acrylate)-naphthopyran mid-functional conjugates 9a-9e.

A12 Appendix 2. Supplementary Material for Chapter 4 ______

10e 10d 10c 10b 10a 1 Normalized GPC Intensity 0 25 27 29 31 33 35 37 Retention Time (mins)

Figure 13. Overlaid and normalized GPC traces of poly(n-butyl acrylate)-naphthopyran mid-functional conjugates 10a-10e.

13c 13b 13a 1 Normalized GPC Intensity 0 25 27 29 31 33 35 37 Retention Time (mins)

Figure 14. Overlaid and normalized GPC traces of poly(n-butyl acrylate)-naphthopyran copolymers 13a-13c.

A13 Appendix 3. Supplementary Material for Chapter 5 ______

Appendix 3. Supplementary Material for Chapter 5 Optimizing the Photochromic Performance of Naphthopyrans in a Rigid Host Matrix using Poly(dimethylsiloxane) Conjugation.

Figure 1. Thermal decolouration behaviour of naphthopyran dyes in solution attributable to the two main classes of open transoid isomers decaying with different first-order rate constants: TT TC and TC CF.

1 Figure 2. Example H NMR spectrum (d6-acetone) of 18b with peak assignments; *HDO, H2O (2.84 ppm).

A14 Appendix 3. Supplementary Material for Chapter 5 ______

1 Figure 3. Example H NMR spectrum (d6-acetone) of 16b with peak assignments; *HDO, H2O (2.84 ppm); # triplet obscured by solvent peaks.

A15 Appendix 4. Supplementary Material for Chapter 6 ______

Appendix 4. Supplementary Material for Chapter 6 Photochromic Behaviour within Polymer Matrices, Part 1: Highly Crosslinked Networks

1 Figure 1. Example H NMR spectrum (CDCl3) of monomer 4 with peak assignments; * DCM (5.30 ppm).

A16 Appendix 4. Supplementary Material for Chapter 6 ______

1 Figure 2. Example H NMR spectrum (CDCl3) of PEG-naphthopyran 2 with peak assignments.

1 Figure 3. Example H NMR spectrum (CDCl3) of naphthopyran monomer 6 with peak # assignments; * H2O (1.56 ppm) and DCM (5.30).

A17 Appendix 5. Supplementary Material for Chapter 7 ______

Appendix 5. Supplementary Material for Chapter 7 Photochromic Behaviour within Polymer Matrices, Part 2: Hyperbranched Polymers

1 Figure 1. H NMR spectra (d6-acetone) of linear poly(methyl acrylate) L3 (top), linear poly(methyl methacrylate) L3 (middle) and linear poly(methyl methacrylate) L1 (bottom) with peak assignments.

A18 Appendix 6. Supplementary Material for Chapter 8 ______

1 Figure 4. H NMR spectrum (d6-acetone) of hyperbranched poly(methyl methacrylate) H1 with peak assignments.

1 Figure 5. H NMR spectrum (d6-acetone) of hyperbranched poly(methyl methacrylate) H3 with peak assignments.

A19 Appendix 6. Supplementary Material for Chapter 8 ______

Appendix 6. Supplementary Material for Chapter 8 The Application of a Photochromic Probe to Monitor the Self-Assembly of Thermosensitive Block Copolymers

Figure 1. Overlaid and normalised GPC traces showing sequential block formation for synthesis of SOX-p(NIPAM)220-b-p(NAM)87 1.

Figure 2. Overlaid and normalised GPC traces showing sequential block formation for synthesis of p(NIPAM)243-co-p(SOX)1.2-b-p(NAM)92 2.

A20 Appendix 6. Supplementary Material for Chapter 8 ______

Figure 3. Overlaid and normalised GPC traces showing sequential block formation for synthesis of p(NIPAM)115-co-p(SOX)1.3]-b-p(NAM)93 3.

Figure 4. Overlaid and normalised GPC traces showing sequential block formation for synthesis of p(NIPAM)178-co-p(SOX)1.6-b-p(NAM)93 4.

A21 Appendix 6. Supplementary Material for Chapter 8 ______

Figure 5. Overlaid and normalised GPC traces showing sequential block formation for synthesis of p(BA)89-b-p(NAM)93 5.

Figure 6. Overlaid and normalised GPC traces showing sequential block formation for synthesis of SOX-p(BA)135-b-p(NAM)104 6.

A22 Appendix 6. Supplementary Material for Chapter 8 ______

1 Figure 7. H NMR (400 MHz, CDCl3) of SOX-p(NIPAM)220-b-p(NAM)87 1 with peak assignments.

1 Figure 8. H NMR (400 MHz, CDCl3) of p(NIPAM)243-co-p(SOX)1.2-b-p(NAM)92 2 with peak assignments.

A23 Appendix 6. Supplementary Material for Chapter 8 ______

1 Figure 9. H NMR (400 MHz, CDCl3) of p(BA)89-b-p(NAM)93 5 with peak assignments.

1 Figure 10. H NMR (400 MHz, CDCl3) of SOX-p(BA)135-b-p(NAM)104 6 with peak assignments.

A24 Appendix 6. Supplementary Material for Chapter 8 ______

1 Figure 11. H NMR (400 MHz, CDCl3) of p(NIPAM)115-co-p(SOX)1.3-b-p(NAM)93 3 with peak assignments.

1 Figure 12. H NMR (400 MHz, CDCl3) of control polymer SOX-p(NAM)84 with peak assignments.

A25 Appendix 6. Supplementary Material for Chapter 8 ______

1 Figure 13. H NMR (400 MHz, d6-acetone) of SOX-p(NIPAM) macro RAFT (precursor to 1) with peak assignments.

1 Figure 14. H NMR (400 MHz, CDCl3) of control polymer p(SOX)1.1-co-p(NAM)93 with peak assignments.

A26 Appendix 6. Supplementary Material for Chapter 8 ______

1 Figure 15. H NMR (400 MHz, CDCl3) of control polymer p(SOX)1-co-p(NAM)93

A27 Appendix 6. Supplementary Material for Chapter 8 ______

Table 1. Decolouration kinetics of SOX-p(NIPAM)220-b-p(NAM)87 1 in water (left) and corresponding DLS measurements (right) vs. temperature (ºC).a

Temp. Temp. D (nm) A b k (min-1) A k (min-1) A h (ºC) 0 1 1 2 2 (ºC) PDI 29.5 20 1.68 1.2827 1.0276 0 0 20 0.053 29.5 22 1.32 1.6914 1.0348 0 0 22 0.066 29.5 24 1.18 2.0510 1.0316 0 0 24 0.067 29.5 26 1.00 2.4756 1.0223 0 0 26 0.063 30.0 28 0.94 3.1881 1.0168 0 0 28 0.057 30.8 29 0.85 3.5694 1.0031 0.0955 0.0061 30 0.078 34.4 30 0.75 3.9134 1.0068 0.2343 0.0070 32 0.058 47.7 31 0.59 4.1654 1.0031 0.2459 0.0114 34 0.029 49.4 32 0.51 4.5874 0.9888 0.7949 0.0173 35 0.014 49.4 33 0.53 5.0984 0.9906 0.7390 0.0194 38 0.004

34 0.43 4.9654 0.9773 0.3966 0.0288

36 0.42 6.3568 1.0129 0 0

38 0.33 8.4718 0.9969 1.0428 0.0121

a Refer to experimental section of Chapter 8 for description of measurements; for both measurements the concentration of polymer in water = 1.2 × 10 -4 M (4.8 mg/mL), based 1 on Mn 38,360 g/mol ( H NMR estimate). b A0 refers to measured absorbance intensity at onset of thermal decolouration period.

A28 Appendix 6. Supplementary Material for Chapter 8 ______

Table 2. Decolouration of p(NIPAM)243-co-p(SOX)1.2-b-p(NAM)92 2 in water (left) and corresponding DLS measurements (right) vs. temperature (ºC).a

Temp. Temp. D (nm) A b k (min-1) A k (min-1) A h (º C) 0 1 1 2 2 (ºC) PDI 15.6 20 1.37 2.8930 0.9648 0.9634 0.0435 20 0.266 15.8 22 1.20 3.6255 0.9809 1.0076 0.0219 22 0.282 15.9 24 1.18 4.6339 0.9615 1.3115 0.0455 25 0.275 17.9 26 0.96 5.9048 0.9416 1.7016 0.0602 27 0.236 21.7 27 0.91 6.4137 0.9663 1.4622 0.0434 28 0.232 25.5 28 0.85 6.8381 1.0212 0.4800 0.0077 29 0.208 28.3 29 0.83 6.6726 1.0175 0.3345 0.0066 30 0.159 30.3 30 0.81 6.6116 1.0080 0.2912 0.0052 32 0.146 30.1 31 0.77 6.7862 1.0121 0.0212 0.0012 35 0.140

32 0.70 7.2285 0.9936 0.7604 0.0069

34 0.59 9.8620 0.9542 4.0762 0.0507

36 0.55 10.736 1.0222 0 0

38 0.45 13.662 1.0249 0 0

a Refer to experimental section of Chapter 8 for description of measurements; for both measurements concentration of polymer in water = 1.0 × 10-4 M (4.1 mg/mL), based on 1 Mn 41,300 g/mol ( H NMR estimate)/ b A0 refers to measured absorbance intensity at onset of thermal decolouration period.

A29 Appendix 6. Supplementary Material for Chapter 8 ______

Table 3. Decolouration of p(NIPAM)115-co-p(SOX)1.6-b-p(NAM)93 3 in water and corresponding DLS measurements (right) vs. temperature (ºC).a

Temp. Temp. D (nm) A b k (min-1) A k (min-1) A h (º C) 0 1 1 2 2 (ºC) PDI 18.1 20 1.80 3.4757 0.9596 0.6265 0.0454 20 0.252 18.2 22 1.57 4.4044 0.9554 0.7937 0.0460 22 0.233 19.1 24 1.36 5.4194 0.9641 0.8513 0.0387 24 0.226 20.9 26 1.16 6.7162 0.9734 1.1720 0.0394 26 0.196 22.6 27 1.09 7.2531 0.9665 0.9499 0.0376 27 0.167 25.2 28 1.02 7.8480 0.9703 1.0941 0.0401 28 0.127 30.1 29 0.95 8.1726 0.9742 0.7973 0.0289 30 0.058 33.6 30 0.92 8.5503 0.9641 1.1322 0.0346 32 0.017 33.9 31 0.86 8.9601 0.9863 1.3305 0.0362 33 0.006 34.2 32 0.82 9.5209 0.9858 1.6122 0.0141 34 0.010 34.4 33 0.78 9.9528 0.9975 1.2508 0.0313 36 0.006

34 0.73 11.1090 0.9841 2.0449 0.0535

36 0.64 13.4440 0.9589 3.0696 0.0555

38 0.54 16.7220 0.9361 4.4444 0.0736

a Refer to experimental section of Chapter 8 for description of measurements; for both measurements concentration of polymer in water = 1.3 × 10-4 M (3.5 mg/mL), based on 1 Mn 26,830 g/mol ( H NMR estimate). b A0 refers to measured absorbance intensity at onset of thermal decolouration period.

A30 Appendix 6. Supplementary Material for Chapter 8 ______

Table 4. Decolouration of p(NIPAM)178-co-p(SOX)1.6-b-p(NAM)93 4 in water and corresponding DLS measurements (right) vs. temperature (ºC).a D Temp. Temp. h A b k (min-1) A k (min-1) A (nm) (º C) 0 1 1 2 2 (ºC) PDI 16.9 20 1.87 3.7376 0.9746 0.6778 0.0390 20 0.244 17.3 22 1.62 4.5608 0.9873 0.9322 0.0309 22 0.235 18.2 24 1.41 5.6587 1.0177 0.9602 0.0205 24 0.227 20.6 26 1.24 6.7994 0.9929 0.71055 0.0171 26 0.199 24.1 28 1.13 7.7877 1.0126 0.9268 0.0236 27 0.175 29.0 30 1.02 8.3080 0.9763 1.1316 0.0288 28 0.130 38.1 31 0.97 8.6960 0.9692 1.2508 0.0331 30 0.035 39.3 32 0.90 9.2352 0.9607 1.4925 0.0382 32 0.007 39.5 33 0.85 9.7262 0.9533 2.2974 0.0450 33 0.017 40.0 34 0.79 10.401 0.9717 1.6842 0.0263 36 0.016

36 0.72 12.536 0.9681 2.2300 0.0291

38 0.61 15.114 0.9738 4.6185 0.0281

a Refer to experimental section of Chapter 8 for description of measurements; for both measurements concentration of polymer in water = 1.2 × 10-4 M (4.2 mg/ml), based on 1 Mn 34,080 g/mol ( H NMR estimate) b A0 refers to measured absorbance intensity at onset of thermal decolouration period.

A31 Appendix 6. Supplementary Material for Chapter 8 ______

a Table 5. Decolouration kinetics of SOX-p(NAM)84 in water vs. temperature (ºC).

Temp. A b k (min-1) A k (min-1) A (º C) 0 1 1 2 2 20 1.83 1.4731 1.0144 1.4747 0.0192 22 1.68 2.0700 1.0092 2.0775 0.0305 24 1.42 2.5766 1.0066 2.5826 0.0314 26 1.10 3.3058 1.0068 3.3077 0.0194 28 0.98 4.1507 1.0065 4.1515 0.0160 30 0.85 5.2334 1.0066 5.2422 0.0167 32 0.69 6.5120 1.0084 6.5153 0.0159 34 0.58 8.1762 1.0097 8.1807 0.0254 36 0.45 10.454 1.0469 10.4900 0.0066 a Refer to experimental section of Chapter 8 for description of measurements; for both measurements concentration of polymer in water = 1.2 × 10-4 M (1.6 mg/ml) based on 1 Mn 12,450 g/mol ( H NMR estimate). b A0 refers to measured absorbance intensity at onset of thermal decolouration period

Table 6. Decolouration kinetics of p(NAM)93-co-p(SOX)1 in water vs. temperature (ºC).a

Temp. A b k (min-1) A k (min-1) A (º C) 0 1 1 2 2 20 0.87 2.1497 0.9074 0.6814 0.1140 22 0.53 2.7806 0.8926 0.9224 0.1264 24 0.34 3.2975 0.7834 1.2658 0.2164 26 0.21 3.8182 0.8807 1.0603 0.1124 28 0.14 4.7410 0.8920 1.1823 0.1060 30 0.10 6.0363 0.8788 1.4281 0.1249 32 0.07 7.0123 0.9076 0.5703 0.0832 34 0.05 8.3058 0.9311 0.4430 0.0450 36 0.04 9.5338 0.8900 0.0298 0.0645 a Refer to Experimental section of Chapter 8 for description of measurements; for both measurements concentration of polymer in water = 1.2 × 10-4 M (1.7 mg/mL) based on 1 Mn 13,900 g/mol ( H NMR estimate). b A0 refers to measured absorbance intensity at onset of thermal decolouration period.

A32 Appendix 6. Supplementary Material for Chapter 8 ______

Table 7. Decolouration kinetics of p(NAM)93-co-p(SOX)1.1 in water vs. temperature (ºC).a

Temp. A b k (min-1) A k (min-1) A (º C) 0 1 1 2 2 20 1.46 2.8557 0.8196 0.8771 0.2148 22 1.32 3.3313 0.8700 0.9638 0.1526 24 1.16 3.8843 0.9193 1.0501 0.1055 26 0.99 4.4479 0.9464 1.1063 0.0638 28 0.87 5.2538 0.9512 1.3277 0.0498 30 0.63 6.3473 0.9137 2.1566 0.1037 32 0.56 7.7496 0.9242 2.4552 0.0908 34 0.42 8.6566 0.9776 1.3673 0.0183 36 0.36 10.372 1.0131 0.3586 0.0056 a Refer to Experimental section of Chapter 8 for description of measurements; for both measurements concentration of polymer in water = 1.2 × 10-4 M (1.6 mg/mL) based on 1 Mn 13,600 g/mol ( H NMR estimate). b A0 refers to measured absorbance intensity at onset of thermal decolouration period.

a Table 8. Capture of SOX-PROP into micelles made from 5 p(BA)93-b-p(NAM)89.

Polymer Polymer D (nm) t h 1/2 A d k (min-1) A k (min-1) A (mg/ml) (mg) PDI (s) 0 1 1 2 2 - 0.24 1.1 6.4 1.83 6.8656 1.0313 0 0

- 0.61 2.8 5.6 1.31 7.7933 1.0309 0 0

52.5 1.21 5.5 4.6 1.29 9.2046 1.0042 0 0 (0.225) 48.6 1.95 8.9 4.3 1.32 10.4540 1.0491 0 0 (0.169) 43.3 4.21 19.2 3.8 1.25 11.5640 1.0363 0 0 (0.115)

Table 9. Decolouration kinetics of SOX-p(BA)135-b-p(NAM)104 block copolymer 6 in water vs. DLS result (Dh).

Polymer Polymer D (nm) t h 1/2 A b k (min-1) A k (min-1) A (mg/ml) (mg) PDI (s) 0 1 1 2 2 49.9 4.40 19.8 4.2 1.18 10.5420 1.0391 0 0 (0.113) a Refer to Experimental section of Chapter 8 for full description of procedure. b A0 refers to measured absorbance intensity at onset of thermal decolouration period.

A33