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7-2010 NOVEL π-CONJUGATED MATERIALS PLUS THEIR CHARACTERIZATIONS AND APPLICATIONS Xiuxian He Clemson University, [email protected]
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NOVEL π-CONJUGATED MATERIALS PLUS THEIR CHARACTERIZATIONS AND APPLICATIONS
A Thesis Presented to the Graduate School of Clemson University
In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Analytical Chemistry
by Xiuxian Susan He July, 2010
Accepted by: Dr. Rhett C. Smith, Committee Chair Dr. Jason McNeill Dr.Jeffrey Anker Dr. Shiou-Jyh Hwu
i ABSTRACT
The theme of this dissertation will focus on the syntheses and characterization of bipyridine (bipy) containing π-conjugated polymers (CPs). Specifically, poly(p- phenylene ethynylene), polyfluorene and poly(p-phenylene vinylene) derivatives have been prepared via Sonogashira coupling, Suzuki coupling and Heck coupling, respectively. Derivatives of poly(p-phenylene ethynylene), polyfluorene and poly(p- phenylene vinylene) are known to have applications in optical and electronic devices.
Through this study, polymers condensed with bulky bipy-containing TAB as one of the copolymer units have shown increased solubility and diminished intrachain/interchain aggregation in solution and in film due to the effectiveness of TAB in controlling the relative orientations of individual polymer chains. The effect of transition metal binding on polymer photophysics have been quantified and monitored by absorption and fluorescence spectroscopy. This series of metallopolymers features optical estimated bandgaps (Eg) of less than 3 eV, revealing their potential applications as light emitting diode and photovoltaic materials.
ii DEDICATION
I dedicate this work to my family, my Mom, my Dad, my brother Joe He and his wife Yao He. This thesis will complete because of their continuous support. To my parents, it‟s them take care of me financially and physically. Make me feel like I am the luckiest person in the world and the best way to say thank you is to graduate from school.
To my brother and his wife, their courage toward life strongly boots my confidence to my future; provide me a good example and attitudes to face the obstacles in my life.
To my best friends, Jason Huang, Fenghai Guo, Man Zhou, Hongyu Chen and everyone from the church, for their constant support. I wouldn‟t be happier without their listening.
To my labmates, Brad and Anshuman my stay in Clemson could be a lot more complicate without their understanding and help.
To my friend and collaborator, Manuel N. Chaur, we had a good time to study all these three hard classes together and thanks a lot with your help in CVs. It‟s your unbeatable manner toward life, make me deeply understand “there is always more solution than problem”.
iii ACKNOWLEDGMENTS
I need to thank many persons for their support, advices, and help during my student career. These persons have offered great help and encouragement for me to pursue my Ph.D, complete my Ph.D and use my Ph.D after I graduate. The first person is my undergraduate advisor Dr. Daniel Rabinovich, without his encouragement to presume graduate study; I probably stop school many years ago. I also owe many thanks to my current advisor Dr. Rhett C. Smith for his wise advices, his patience, his kindness, his time, his support and his help to me for the past four years. He is a person devotes all he has to his group and fortunately, I am part of his group. Dr. Jeffrey Anker, Dr. Jason
McNeill and Dr. Shiou-Jyh Hwu are my committee members; I thank them for their valuable comments and questions for pre-oral and defense. I also need to thank them for their time to attend my pre-oral and defense. This thesis will not be possible without their signature. To the Smith group, especially Brad Morgan, Anshuman Mangalum, I really appreciate your help, your comments, and understanding in many ways. At the end, I would like to thank Clemson chemistry department offered me the opportunity to study here.
iv TABLE OF CONTENTS
Page
TITLE PAGE ...... i
ABSTRACT ...... ii
DEDICATION ...... iii
ACKNOWLEDGMENTS ...... iv
LIST OF TABLES ...... vii
LIST OF FIGURES ...... viii
LIST OF SCHEMES...... x
LIST OF CHARTS ...... xi
LIST OF SYMBOLS AND ABBREVIATIONS ...... xii
CHAPTER
I. INTERACTIONS OF ORGANIC MATERIALS WITH LIGHT ...... 1
Origins of light absorbing species in organic electronic materials ...... 1 Extent of π–conjugation and its effects on bandgap ...... 2 Applications of π–conjugated polymers ...... 3 From insulators to semiconductors-explanation from band theory ...... 4 What happens when a molecule get excited ...... 6 Excitons-transporter of energy between ground and excited states ...... 9 Basic operation principles behind (O)LEDs ...... 11 Basic mechanisms of organic solar cells ...... 14 Applications of conjugated polymers in biosensing ...... 16 Polymers of interest ...... 17 Different types of polymers feature conductivity ...... 18 π–conjugated poly(p-phenylene ethynylene) derivatives ...... 20 π–conjugated poly(fluorene) derivatives ...... 22
v
II. A BIPYRIDYL CHROMOPHORE-MODIFIED SEMIFLUORINATED POLYMER ...... 25
Introduction ...... 25 Results and Discussion ...... 27 Conclusions ...... 38
III. STERIC COORDINATION CONTROL IN CONDUCTING POLYMERS ...... 53
Introduction ...... 53 Results and Discussion ...... 57
IV. POTENTIAL BIOSENSOR FOR PHOSPHATE IONS ...... 85
Phosphate ions in biological system ...... 86 Results and discussion ...... 89 Conclusions ...... 96
V. CONCLUSIONS AND FUTURE DIRECTIONS...... 98
REFERENCES ...... 100
COPYRIGHT PERMISSIONS ...... 110
APPENDICES ...... 120
A: NMR spectra ...... 120 B: UV-vis and photoluminescence spectra ...... 143 C: Single crystal X-ray diffraction structure ...... 229
vi LIST OF TABLES
Table Page
2.1 Dissociation constants and photoluminescent quenching characteristics of P1 ...... 31
3.1 Select Photophysical Properties of Polymers ...... 63
3.3 Electrochemical and Band Gap Data ...... 68
4.1 Absorption data and photos demonstrating the range of colorimetric responses ...... 91
vii LIST OF FIGURES
Figure Page
1.1 Schematic representation of relative orbital energies in a generic organic molecule ...... 2
1.2 Jablonski diagram of organic molecules depicting excitation states and energy transfer process ...... 6
1.3 Creation of excitons in semiconductor using Wannier-Mott (WM) theory ...... 8
1.4 Energy transfer between donor and acceptor...... 10
1.5 Interactions between organic molecules and dopants ...... 11
1.6 Structural representation of TDP, Alq3 and MEH-PPV and schematic setup of an OLED ...... 13
1.7 Movements of separated holes and electrons in ground and excited states ...... 16
1.8 Common studied polymers...... 17
1.9 Structure of poly(vinylpyridine) and poly(2,2‟-bipyridine)-Ru(bpy)2...... 19
2.1 Absorption spectra for P1 ...... 30
2.2 Progressive changes in the fluorescence spectrum of P1 ...... 33
2.3 Changes in absorption and fluorescence of Zn2+-P1 ...... 35
2.4 Changes in fluorescence of Cu2+-P1 ...... 37
3.1 Schematic illustrating of steric coordination control strategy ...... 53
3.2 ORTEP drawing (50% probability ellipsoids) of [PdCl2(BrTABBr)] ...... 59
3.3 Absorption and photoluminescence responses of PF1 and PPE1 ...... 65
4.1 Titration of ZC with Zn2L1 followed by phosphate displacement test and pyrophosphate displacement test ...... 93
viii LIST OF SCHEMES
Scheme Page
2.1 Synthesis and structure of P1 ...... 28
3.1 Preparation of Bulky Bipy Monomers ...... 58
3.2 Preparation of Bulky Bipy Polymers ...... 61
4.1 Generalized representation of the signal transduction mechanism for indicator displacement assays (IDAs) ...... 86
ix LIST OF CHARTS
Charts Page
3.1 CPs (A) and Bipy-Derivatized CPs (B) ...... 54
3.2 Materials Featuring Sterically Enshrouded 2,2‟-Bipyridyl Units ...... 55
4.1 Dinucleating ligand and complexometric dyes used in the current study...... 88
x LIST OF SYMBOLS AND ABBREVIATIONS
Å armstrong(10-10)
Ф quantum yield
A acceptor
Alq3 tris-(8-hydroxyquinoline)
ARS alizarin red S
BhJs bulk-heterojunction devices
BPR bromo pyrogallol red
Bipy 2,2‟-bipyridine
C60 fullerene
CB conducting band
CDCl3 chloroform
C-IDAs colorimetric indicator-displacement assays
CMPs conducting metallopolymers
CP conjugated polymer
CV cyclic voltammetry
D donor
DCM dichloromethane
DMF dimethylformamide
DMSO dimethyl sulfoxide
DNA deoxyribonucleic acid
DSC differential scanning calorimetry
xi DT dithizone
EA electron affinities
EBBB eriochome blue black B
Eg bandgap energy
ERB eriochome red B
ET electron-transporting
ETL electron-transporting layer
FAVE fluorinated aromatic vinylene ether
FRET Forster resonance energy transfer
GC gallocyanine
GPC gas permeation chromatography
H-bpmp 2,6-Bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol
HEPES 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid
HOMO highest occupied molecular obital
HT hole-transporting
HTL hole-transporting layer
ICP intrinsically conducting polymer
IDAs indicator-displacement assays
IE ionization energry
IP ionization potential
IPs inorganic phosphates
ITO indium tin oxide
xii K potassium
Kd dissociation constant
LED light emitting diode
LUMO lowest unoccupied molecular orbital
MEH-PPV poly[2-methoxy,5-(2‟-ethylhexyloxy)-1,4-phenylene-vinylene]
MLCT metal to ligand charge transfer
Mn number average molecular weight
Mw weight average molecular weight
MX murexide
NMR nucleic magnetic resonance
NO nitric oxide n nano (10-9)
(O)LED (Organic) light-emitting diodes
OPs organophosphorus
OPV organic photovoltaic
OSCP organic semiconducting polymer
PA polyacetylene
PAR 4-(pyridin-2-ylazo)resorcinol
PDA poly(diacetylene)
PE polyethylene
PF polyfluorene
PF1 PF-TAB
xiii pi phosphate
PL photoluminescence
PPE poly(p-phenyleneethynylene)
PPE1 PPE-TAB
PP poly(phenylene) ppi pyrophosphate
PPP poly(p-phenylene)
PPV poly(p-phenylenevinylene)
PV photovoltaic
BrTABBr 5,5‟-bis(4-bromo-2,6-dimesitylstyryl)-2,2‟-bipyridine
ITABI 5,5‟-bis(4-iodo-2,6-dimesitylstyryl)-2,2‟-bipyridine ppb parts per billion ppm parts per million
PT poly(thiophene)
PV pyrocatechol violet
PV photovoltaic
PVC polyvinyl chloride
PVP poly(vinylpyridine)
RNA ribonucleic acid
S0 single ground state
S1 singlet excited state
T0 triplet ground state
xiv T1 triplet excited state
Td decomposition temperature
Tg glassy transition temperature
TGA thermogravimetric analysis
THF tetrahydrofuran
TPD N, N‟-diphenyl-N-N‟-bis(3-methylphenyl)-1,1‟-biphenyl-4,4-
diamine
UV-vis ultra-violet visible
VB valence band
WM Wannier-Mott
ZC zincon
xv CHAPTER ONE
INTERACTIONS OF ORGANIC MATERIALS WITH LIGHT
1.1 Origins of Light Absorbing Species in Organic Electronic Materials
Organic π-conjugated materials have received great attention since the first organic light-emitting diode (OLED) was reported in 1987.1 The finding signaled the birth of a revolution in display technology. An attractive feature of π-conjugated organic materials is their light absorbing ability which provides an avenue for harvesting solar energy that we can utilize for free from the sun. Ultraviolet-visible radiation is the preferred target absorption region for organic electronic materials due to the assessable bandgap energy. The lifetime of excited species in such materials is typically on the order of nanoseconds (10-9 s). Upon radiation, excitation energy is lost by photochemical relaxation (given off as heat or emission in terms of fluorescence or phosphorescence
(given off as light) or is transferred from donors to acceptors.2 In most cases, since the concentration of organic materials in solutions of study are relatively low (µM), the thermal changes of the solution are negligible and hence, in all the studies reported in my thesis, we will assume the disturbance of thermal relaxation to our systems of interest is minimal and only photon-electronic transitions will be considered.
There are three types of orbitals involved in electronic transitions in π-conjugated materials. Bonding orbitals of σ, σ*, π, π* and nonbonding orbital n. All organic molecules have the abilities to absorb light energy; as seen in Figure 1.1. Absorption of light leads to electrons in bonding-orbitals such as σ, π, and n to absorb necessary
1 energies of E1, E2, E3 or E4 respectively to promote electrons to the next lowest excitation state, often to an anti-bonding orbital. E1 is relatively high (λ≤185 nm under vacuum) and thus occurs rarely. In all the organic molecules of interest in these studies, energy band- gap of these organic molecules are between E2 and E3 and limited to chromophores with low excitation energies (200 nm≤λ≤700 nm) with possible transitions of n or π to π*.
σ*
π*
E2 E4 Energy Increase E1 E3 n
π
σ
Figure 1.1 Schematic representation of relative orbital energies in a generic organic molecule.
1.2 Extent of π–conjugation and its Effects on Bandgap
When a molecule has many π-bonds and of those are alternated by single bond between double bonds, an extended π-conjugated system will generate. The influence of a
π-conjugated system comes from its dictation to the band-gap between bonding and anti- bonding orbitals. Since a π-conjugated system is made up of a chain of overlapping p
2 orbitals, each of these are separated by a single bond in between, leading to the spread of electron density along π-conjugated chains and delocalization of charge. The delocalization of π-electrons in turn lowers the bandgap and thus requires less energy to promote electrons from bonding (HOMO-highest occupied molecular orbital) to anti- bonding (LUMO-lowest unoccupied molecular orbital) orbitals. The lower the bandgap energy level, the longer the wavelength (bathochromic) will be observed in UV-Vis region. In contrast, higher the bandgap energy, the more blue shift (hypsochromic) will be observed in shorter wavelength region. In some case, the non-bonding electrons are solvated by polar solvents which lowers the energy level of unbounded electrons lower due to the hydrogen bonding between non-bonding electrons and solvent molecules.
These types of π-conjugated systems with low valence-conduction bandgaps is easy assessable upon excitation radiation and they are the major interest in the field of conducting metallopolymers.
1.3 Applications of π--conjugated Polymers
There are three major areas in which we can apply our semiconducting polymers: organic light emitting diode (OLED) which manipulates electrical energy into light; solar cells, which apply CPs‟ photovoltaic ability to conduct electricity upon the excitation with light; and sensors in which devices are utilizing chemical or physical stimulus to alter the emission or electron flow, to achieve sensing purposes. The later is the major focus of Chapter Two. Our materials have great potential in detecting explosive, toxic, and diagnosing all these life threatening issues though the physical-optical changes upon exposure to target analytes. This work presented in this chapter was published in Journal
3 of Material Chemistry (Copyright 2008, The Royal Society of Chemistry). The citation for this manuscript is: Susan He, Scott T. Iacono, Ashlyn E. Dennis, Dennis W. Smith, Jr.
Rhett C. Smith. Photoluminescence and ion sensing properties of a bipyridyl chromophore-modified semifluorinated polymer and its metallopolymer derivatives.
Journal of Materials Chemistry, 2008, 18, 1970-1976.
At the same time, all three applications require one common feature from CPs, which is organic semiconducting polymer (OSCP) have to be easily oxidized (p-doped) by removing (an) electrons and reduced (n-doped) by accepting (an) electrons from dopants or other external sources such as electrode input. The external physical or chemical stimuli to CPs by light radiation or charge transfer allow electrons move freely between valence-conducting band-gap which creates conductivity.
1.4 From Insulators to Semiconductors-Explanation from Band Theory2
Polymers like polyethylene (PE) and poly(vinyl chloride) (PVC) are insulators due to their poor conductivity (<10-10 ohm-cm-1). After the discovery of polyacetylene‟s conductivity (PA) in 1977, scientists started looking into the conducting mechanism behind the whole process. At the beginning, it was only thought that the process was originated from the creation of an unpaired electron (free unpaired electron, also referred as polaron) by simple oxidation or reduction, but later people found out that the conducting mechanism is more complicate. Scientist took a step back to find out what was happening at the molecular level after the removal of an electron from the valence band or addition of an electron to the conduction band.
4 Polymers are made up of monomers which are built from a large number of atoms
(C, H, N etc.). From band theory point of view, valence electrons make up orbitals. Those with same level of electronic energy, and geometries will combine and split into two major energy states, forming bonding orbitals and anti-bonding orbitals. Orbitals with similar energy level will align and will stay next to each other to form continuous bands.
Explained by Huckel‟s theory, a π-bond will form upon interaction with two sp2 hybridized orbitals from two p orbitals of adjacent molecules. The highest occupied molecular orbitals (HOMO) by electrons is called valence band (VB) and the lowest unoccupied molecular orbital (LUMO) is referred as conducting band (CB). HOMO and
LUMO are separated by energy Eg. In the case of a polymer chain, the longer the π- conjugated system, the more interactions between sp2 hybridized p orbitals of each other which creates large domains of HOMO band (made up of π-bonding orbitals) and LOMO band (make up of anti-bonding orbitals). Electrons are filled start from the lowest energy ground state HOMO then move to the next LUMO states. If HOMO (highest occupied state) is completely full, and LUMO is completely empty, energy input is required for removing an electron from HOMO. The minimum amount of energy that required to promote electrons from HOMO to LUMO is referred as bandgap energy (Eg). The magnitude of bandgap energy dictates if the polymer is an insulator or semiconductor.
For conductors, there was no band-gap between HOMO and LUMO with Eg = 0 eV. In semiconducting organic materials, unlike common polymers which have poor electron mobility, the bond alternation in π-conjugated systems of most CPs cause a lower band- gap allowing achievable transition between valence band and conduction band in
5 semiconductor.3 In the case of insulator, the situation is more complex. The bandgap between HOMO and LUMO are so large that it requires more input to simply remove an electron thermally or photolytically. Even though, the discovery of poly(acetylene) (PA) which was capable of conducting electrons with the aid of a small amount of dopants.
The new finding leads to a new broom of polymer generation. The specific functional mechanism was not well explained back to that time; rather, people referred this phenomenon as a redox process which involves charge transfer with subsequent creation of charge species.3 The doping process is rather simple, could be carried out in gas phase, solution or electrochemically.3
1.5 What happens when a molecule get excited?
Forster, Dexter or radiative energy transfer Intersystem S 1 crossing
T 1
Absorption Fluorescence Phosphorescence (-hv) (slowly give off light) (+hv)
S 0 S 0
Figure 1.2. Jablonski diagram of organic molecules depicting excitation states and energy transfer process.3
In order to better understand the mechanism behind semiconducting polymers, it is necessary to find out what happens when organic molecules get excited by radiation.
From a quantum point of view, molecules vibrate and rotate at a faster rate than normal
6 upon excitation. If the required bandgap energy reaches, molecules would go to the first single excited state S1 from S0 through electronic transitions (Figure 1.2), followed by internal conversion, then proceed to emission or non-radioactive decay. The second pathway would be achieved if the experiment was carried out at low temperature or coupled with triplet dye-sensitizing excited state molecules. Once the energy level matches, the singlet excited state will go through intersystem crossing to reach triplet excited state T1. S1-T1 intersystem crossing occurs rarer than S0-S1 because transition between T1 to S1 is forbidden. The third pathway is the Frȍster and Dexter energy transfer. It involves the energy transfer between donors (D) and acceptors (A). The lifetime and medium surrounding of excitons dictate the electronic energy transfer pathways. They are the product of light and organic molecules and are responsible for energy transfer. In other words, excitons are created by light radiations. The direction of excitonic movement and mobility distances dictates their potential applications (Figure
1.3).
Upon the absorption of a photon, an electron in valance band gets the energy needed to escape away from the band then raised to the conduction band, and an empty electron hole is left behind in the valence band. An electron and a hole are created upon photon excitation. If both the electron and hole are separated, a polaron will form. If an electron and the hole interact due to electrostatic charges, an exciton will form. Explained by Wannier-Mott (WM) theory, WM excitons have long extended radius of 40 ~ 100 Å due
7 Conduction band
e- (polaron) Photon excitation e ---- e e e e + exciton
Valence band
Figure 1.3 Creation of excitons in semiconductor using Wannier-Mott (WM) theory.2
to the overlap of neighboring atoms shielding the Columbic interaction between the electron and hole; thus, the exciton serves as a dielectric continuous band.2 The formation of polaron and exciton are created in femtoseconds (10-15 s). Alternatively, the electron or hole may be captured again in femtoseconds, by impurities or defects that provide lower energy level. C60 derivatives are examples of strong electron acceptors that can be used as catchers. The location of the polaron levels relate to the conductive band edge or valence band edge depends on the π-conjugation length of the polymer.2 Upon light radiation, the removed electron and the left behind holes are isolated, form polaron which locates between the conducting band and valence band symmetrically. Depending on the length of the conjugated system, the longer the π-conjugation, the less deformation effects as a result of the loss of an electron, lead to less relative energy carried by the polaron. Hence the polaron stays closer to both the conducting band and valence band edge within a smaller bandgap. For shorter conjugation lengths, the band gap would be larger; polaron
8 locates further away from both conducting and valence band edges within a bigger bandgap. As a result, the electrostatic interaction between the two causes minor chain deformation or relaxation. Excitons can be singlets because they are after created with opposite charges (spins ±1/2). There should be multiple types of excitons due to different energy levels between conduction band and valence band. Bipolarons also exist when two like charges with opposite spins bound together within the same conjugation length.
The bipolaron occupy two levels in the gap. Another possibility of spin pairing is between like-charged polarons on different chains (nearby oppositely charged ions donated the charges to the chain). There would be only one strong transition by bipolaron.
1.6 Excitons – Transporter of Energy between Ground and Excited States
Upon photon excitation, removal of an electron creates an empty space for other electrons to jump in; movements of the electrons in valence band become more flexible.
Thus, the mobility of an excited state of a molecule is referred to as an exciton.2
Excitonic diffusion is major pathway account for energy transfer between excited states and ground states and it is also responsible for luminescence and photoconductivity. 2 In solids, due to close packing of molecules, excitons can reach to a couple of molecule radius distances (delocalized). Depending on the amplitude of delocalization, for organic semi-conductive molecules, the excitions are called Frenkel excitons2 which referred to the electron-hole pair localized on a single molecule (<5 Å), which is also considered as a neutral item has no net charge but the electric field generate is able to polarize its surrounding lattice and forms polaronic quasiarticles.4
9
Figure 1.4. Energy transfer between donor and acceptor.2
Once excitons are generated, how are excitons involved in energy transfer? Figure
1.4 depicts the possible pathways for excited molecules to transfer their energy and back to ground states. Forster energy transfer describes singlet–singlet transitions well.
Applying Forster excitons theory, multiple polarized diploe-dipole interactions are summed up and create a channel for energy transfer between donor (D) and acceptor (A), and the rate of energy transfer depends on the distance between the two. Only transitions of the same spins are allowed. In addition to Forster‟s theory, which explains singlet transitions well; Dexter‟s theory is a better fit for triplet energy transfer, which requires no allowed transitions on both the donor and acceptor molecules, as long as the D and A have enough overlap in energy. Excitons could diffusively hop from D to A with no change in spin. The limitation is Dexter energy only occur if D and A are in close proximity with each other (~10 Å), so it only occurs restrict to neighbor molecules.
10 1.7 Basic Operation Principles behind (O) LEDs
Organic semiconducting materials have proven applications in light emitting devices.2 As mentioned earlier, LEDs are devices that turning electric energy into light.
The simplest OLED configuration is the single organic layer device composed of an electron-transporting (ET) or hole-transporting (HT) organic layer sandwiched between a cathode and an anode.2 The organic thin film serves dual roles in OLEDs, charge carrier and electroluminescence emitter. Excitons are formed near the contact sites of HOMO and anode as well as LUMO and cathode (Figure 1.5).
e- e- e- e- e- e- e- Cathode (reduction) LUMO N-doped high density of free e- e-
HOMO e- e- e- e- e- e- e-
Anode (oxidation) P-doped high density of free holes
Organic molecules Dopants
Figure 1.5. Interactions between organic molecules and dopants.
Depending on the morphologies of different π-conjugated systems, the mobilities of excitons are different, leading to some cases where excitons recombine with each other, resulting in complete or partially quench of luminescence. The basic physical processes happen in OLEDs are charge injection into the undoped organic semiconductor from the metallic contacts, follow by charge transport and electron-hole recombination in organic films.5 Improved luminescence efficiency of recombinant of ETL by using
11 aluminum tris-(8-hydroxyquinoline) (Alq3) and HTL by using N,N‟-diphenyl-N-N‟- bis(3-methylphenyl)-1,1‟-biphenyl-4,4-diamine (TPD) suggests that exciton recombination occurs near the ETL-HTL interface which can extend the exciton diffusion length to 100-300 Å.6,7,8 By applying high luminescence efficient p-type dopants or n- type dopants, the host exciton can transfer its energy to a luminescent dopant molecule or the dopant might render an electron or a hole trap for mobile carriers, in both case can lead to exciton formation in the dopants.2 This process requires the concentration of dopant to be very low (<0.1%).
Small molecules like TPD and Alq3 have proven practical for use in OLEDs by
1987.1 The first promising polymer was not reported until three years later.9 In the schematic set up for an organic LED displayed in Figure 1.6, calcium was used in the metal contact as high electron density cathode, and indium tin oxide (ITO) was transparent high density holes at anode. MEH-PPV was sandwiched between cathode and anode. The injected electrons from cathode and holes from anode recombine in an un- doped MEH-PPV film cause the formation of excitons and emittion of light when relax.
Organic films made up of small molecules such as TPD work similarly as polymer films. In general, polymer films have better rigidity than films of small organic molecules due to longer π-conjugated polymer chain and strong inter(intra)chain
12
Figure 1.6 Structural representation of TDP, Alq3 and MEH-PPV and schematic setup of an OLED.2,5
crosslinking compare to weak Van der Waals interactions that hold molecules together in small molecule device.5 Energy band-gaps of thin-film (100 nm) organic semiconductors are between 2 eV to 3.5 eV and could be prepared by thermal evaporation in vacuum or spin casting.5
13 1.8 Basic Mechanisms of Organic Solar Cells
Photovoltaic (PV) devices are being increasingly recognized as one of the key beneficial devices designed for global consumers due to its ability to convert free sunlight into electric power. Due to the limited natural fuel sources and increasing cost of fuel energy, PV devices production become one of the fastest growing industry with $5.8 billion worldwide sales increment in year 2004.5 The purposes of using PV devices are understood, but the high cost overhead to produce PV devices limit its massive manufacturing and applications. The average cost of electricity generated from PV module is about 10 times more expensive than regular fossil fuels and 3 times more expensive than other renewable energy. 5 There are three different kinds of material available for PV manufactures: Si thick film, inorganic thin film and organic semiconductor. These materials‟ cost, efficiency, and robustness dictate their overall performance and productions. Organic semiconductor based PVs is grouped as the third generation PV device which offers low cost, high efficiencies.5 The well known dye- sensitized nanosturctured oxide solar cells are based on ultilization of an organic dye to
10 absorb light and undergo a rapid electron transfer to nanosized TiO2 as acceptor. The hole transport could be achieved by a redox couple iodide/triiodide (I/I3).5 This kind of solid-state bulk-heterojunction devices (BhJs) has shown similar results by using light absorbing conjugated polymers with inorganic semiconductors such as CdS, ZnO, CdSe,
PbS as donors and acceptors. Organic conducting polymers based OPVs using poly(3- hexylthiophene) as donor and a fullerene derivative as acceptor are attracted the most attention.5 Significant amount of research is still ongoing for the development of OPV,
14 but OPV have many promising features from the benefit of costs, efficiencies and environment protection.
In organic solar cells, the absorption of photons leads to the formation of free electrons and holes. They are bound together by electrostatic interaction to form excitons.
The energy required for the formation of excitons is range from 0.05 eV up to 1 eV. 11
Excitons could do some random walking movement for a length of 5-15 nm before decay to give off light.5 This phenomenon also known as exciton diffusion. In OPV, light is absorbed to convert electricity. Organic polymers applying in have to be able to stabilize or extend the lifetime of excitons. They are capable of turn excitons into charge carriers
(carry electrons), to serve as “electrolyte” supports conducting current. Excitons need to be separated into free charge carriers before decay (give off light), and this phenomena is known as exciton dissociation.5 This process requires input of energy to overcome the
Coulomb‟s forces between electron and hole. Different ways have been reported in literature including using trap sites in bulk material12, applying electric field13, heat supply14, and dropping potentials at the interface between donor and acceptors15.
Photophysics of bilayer interface between donor (CPs) and acceptor (C60) has been reported.16 In Figure 1.7, the fast electron transfer between LUMO of donor and
15 D D D* A* A A
Figure 1.7 Movements of separated holes and electrons in ground and excited states.
LUMO of acceptor separates the electron and the hole. The free electron and hole pair is responsible for the transportation of free charges to their surrounding during their lifetime
(milliseconds) and the fastest electron transfer observed in this case (CP and fullerene) is within 45 fs (10-12 s) which is 3 magnitudes faster than decaying process (10-12 s).16
1.9 Applications of Conjugated Polymers in Biosensing
The third application highlighted at the beginning of introduction is bio-sensing which applys chemical or physical stimulus to alter CP emission or conductivities. Great effort has been spent on developing novel materials for bio-molecular detections.
Macromolecules like DNA helices, RNA chains, and protein aggregates are in the center of research now due to their essential and important roles in biological field. Small molecules like phosphate/pyrophosphate, metal ions (Ca2+, Zn2+, Na+, K+, etc), and glucose are also required in cellular regulations. Hence, detection of bio-related small molecules is also crucial to understand diseases. The goal of development new sensing
16 materials is aimed to suit for selective, sensitive, rapid and economic detection and analysis. Many interesting methods have been reported in literature; detections of bio- molecules coupling molecular beacons, nano-particles, redox-active species as labels have shown some results in analysis. Born in the same generation, practices of coupling
CPs with other technique in detecting DNA, RNA, proteins and even some pathogenic bacteria have shown impressive results.4, 17-20
1.10 Polymers of interest
Polymers used in bio-molecular detections are capable of absorbing light in UV- visible region and able to generate a signal upon detection. Aqueous solubility could achieve by attaching hydrophilic groups to polymer backbones. Polydiacetylenes, poly(fluorene-alt-phenylene)s, polyfluorene, polythiophenes, poly(p-phenylene)s, poly(p- phenylenevinylene)s, poly(p-phenyleneethynylene)s, polypyrroles, and polyaniline are commonly seen polymers reported in literature. 5
Figure 1.8 Common studied polymers.
17 Derivatives of poly(diacetylene)-PDA, poly(thiophene)-PT were shown their abilities to detect interactions between proteins21-25, virus, whole cells by colorimetric (color changes) and fluorometric (give off light) methods.5 Poly(fluorene)-PF, poly(phenylene)-
PP, poly(phenyleneethnylene)-PPE and poly(p-phenylenevinylene)-PPV are the interest of my study. These kinds of polymers are very practical for applications due to the following: allow to detect target analytes at low concentration ( 1.11 Different Types of Polymers Feature Conductivity A. Intrinsically Conducting Polymer An organic polymer displays the electrical and optical properties of a metal while retaining its mechanical and processable abilities, this kind of polymer termed an intrinsically conducting polymer (ICP).24 Unique feature of ICPs is the presence of alternating single and double bonds along the polymer chain, which allow delocalization or hopping of excitons along the polymer backbone.23 The conductivity of ICPs arise from the delocalization of π-bonded electrons over the polymer backbone. The more delocalized the π electrons, the more electronic effects the polymer will exhibit. In turn, the polymer will lower the energy bandgap between HOMO and LUMO; low ionization potentials (IP) and high electron affinities (EA).23 18 B. Redox Polymers In „conducting conjugated polymers‟, the redox sites are delocalized over a conjugated system. They are well known to transport electrons by hopping or self- exchange between donor and acceptor sites.24 But the redox conductivity is relatively lower than that of conjugated conducting polymers due to slow electron transport to or from the redox center.24 The first generation of redox polymers are primarly made up of a polymer backbone with a pendent transition metal or metal complex off polymer backbone such as poly(vinylpyridine) (PVP).26 More recently a new generation of redox polymer named conjugated metallopolymers bloomed as a hybrid of conjugated polymers and transition metals.10, 11 The highlight feature of this class of materials is that metal is coordinated directly to the conjugated backbone of the polymers compared to the pendant coordination with vinyl groups of traditional redox polymer. This type of hybrid affords a direct electronic interaction between the electro-active metal centers and electro-active polymer backbone; it can also facilitate electron transport in the polymer backbone, draw many applicable optic and electronic chemical transitions. Figure 1.9. Structure of poly(vinylpyridine) and poly(2,2‟-bipyridine)-Ru(bpy)2. 19 1.12 π-conjugated Poly(p-phenylene ethynylene) derivatives CPs targeted in applications of biosensing such as DNA, RNA, proteins, and other important biomolecules have been applied based on their optical and electrochemical signals produce upon interaction with target anaylte. PPE derivatives are one of them. Functionalized PPE with mannose has been used to detect pathogens on surfaces without lysing cells to extract DNA and RNA and offers good signals.5 Superquenching of PPE by proteases offer another way to detect biotin/avidin interaction. 5 1.13 π-conjugated Poly(p-phenylene vinylene) derivatives Poly(phenylene vinylene) (PPV) and its derivatives are mainly used as LEDS materials. Here we used frontier π electronic structure and show how the substituent influence it. In all PPV polymers, they shared the common repeating unit, a benzene ring and a vinylene group. Derivatives of PPVs would have substituent on benzene ring or on vinylene or both. The formations of delocalization of π electrons come from the alternating single and double bonds. Electron densities along para-position of the benzene ring overlaps with the π state of vinylene group, the orbital interactions lead to the dispersed highest lying π band of PPV (HOMO).2 Meta and ortho position of the benzene ring due to wrong orbital geometries, electrons localized on ortho carbons result in no overlapping with the highest π state of the vinylene group, make up the second highest lying π band of PPV (LUMO).2 When substituents are added to the polymer backbone, it could be added on benzene ring or vinylene group. The electronic structure of the polymer backbone can 20 be altered depend on the substituents. If the substituents R are added to the π-conjugated polymer backbone, R could stabilize (R is electron donating group) or destabilize (electron withdrawing group) the π bands.2 The steric effect from R also need to take into consideration due to the bulkiness of R would induce a conformation changes in the torsion angle between the benzene ring and the vinylene group. An increase of the torsion angle will lead to change in orbital geometries and have more effect in separating the overlapping. Thus, wisely locate the R group into the π-conjugated systems would optimize the stability of the polymer backbone and orbital interactions. The stability and π-conjugated systems have great impact on bandgap, electronic properties. Studies of conducting metallopolymers have become increasing important due to the metal contact involved in electronic applications of conducting polymers. For example, PPV has low electron affinity, which means it does not like much to accept electrons. Low EA limits the metal could be used as electron injection source for PPV, gold and aluminum need to cross a large energy barrier to achieve electron injection to PPV compare to alkali metals.2 In order to optimize PPV-based device performance, it is very important to investigate metal binding ability of polymers including charge- injection, interface stability (how fast the diffusion rate is) under certain conditions.2 A change in the chemical and electronic structure of the polymer film due to the binding of metal could significantly improve or degrade the overall performance of the device.2 1.14 π-conjugated Poly(fluorene) derivatives Cation polyfluorenes was reported in biodetection by Bazan, et. al.5 The basic operational principle in this application is based on Forster resonance energy transfer 21 (FRET) between energy donor and acceptors. The interaction between the two is electrostatic interactions. When the cationic PF excited by light, it will transfer its energy to chromophore acceptor in close proximity. There are two requirements for this detection to occur, the close distance between donor and acceptor and negatively charge acceptor due to electrostatic interactions are the driving force to draw the donor and acceptor to close proximity. A dizinc enzyme model synthesized for phosphate ions detection was also included and detailed in this dissertation. This work was presented in chapter four and was published in Inorganic Chemistry (Copyright 2007, American Chemical Society). The citation for this manuscript is: Brad Morgan, Susan He, Rhett C. Smith. Diznic Enzyme Model/Complexometric Indicator Pairs in Indicator Displacement Assasys for Inorganic Phoshphates Under Physiological Conditions. Inorganic Chemistry, 2007, 46, 9262-9266. 22 REFERENCES CITED 1. Tang, C. W. V. S., S. A., Applied Physics Letter, 1987, 913-915. 2. Organic Electronic Materials Conjugated Polymers and Low Molecular Weight Organic Solids. Springer-Verlag Berlin Heidelberg, Germany, 2001. 3. Electronic and Photonic Applications of Polymers. American Chemical Society: Washington, DC, 1988. 4 McQuade, T.D.; A. E. P.; Swager, T.M., Chemistry Review 2000, 2537-2574. 5. Semiconducting Polymers Chemistry, Physcis and Engineering Wiley, Germany, 2007. 6. Stolka, M.; J. F. Y.; Pai, D. M., The Journal of Physical Chemistry, 1984, 4707- 4714. 7. Kepler, R. G.; a. P. M. B.; Jacobs, S. J.; Anderson, R. A., Sinclair, M. B., Valencia, V. S.; Cahill, P. A., Appl. Phys. Lett. 1995, 66 3618-3620. 8. Lin, L. B. J., S. A.; Young, R. H.; Borsenberger, P. M., Applied Physics Letters, 1997, 2052. 9. Burroughes, J. H. B., D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B., Nature, 1990, 539-541. 10. O'Regan, B.; Gratzel, M., Nature 1991, 353 737-740. 11. Gregg, B. A., The Journal of Physical Chemistry B 2003, 107 4688-4698. 12. Brian, A. G.; Mark, C. H., Journal of Applied Physics 2003, 93 3605-3614. 13. Popovic, Z. D.; Hor, A.M.; Loutfy, R. O., Chemical Physics 1988, 127 451-457. 23 14. Arkhipov, V. I.; Emelianova, E. V.; Bassler, H., Physical Review Letters 1999, 82 1321. 15. Handbook of Organic conductive Molecules and Polymers. Wiley, 1997. 16. Zerza, G.; Brabec, C. J.; Cerullo, G.; De Silvestri, S.; Sariciftci, N. S., Synthetic Metals 2001, 119 637-638. 17. Wang, J., Chemistr -A European Journal, 1999, 1681-1685. 18. Englebienne, P., Journal of Material Chemistry 1999, 1043-1054. 19. Bazan, B. L. a. G. C., Chemistry of Materials 2004, 4467-4476. 20. Leclerc, M.; H.A. H., Synlett 2004, 380-387. 21. Wilson, T. E.; W. S.; Deborah H. C.; Bednarski, M. D., Langmuir 1994, 1512- 1516. 22. Ma, Z.; J. L.; and Jiang, L., Langmuir 1999, 489-493. 23. Patil, A. O.; Heeger, A. J.; Fred Wudl, Chemistry Review 1988, 183-200. 24. Self-Doped Conducting Polymers. Wiley, 2007. 25. Sofiya Kolusheva, L. B. R. J., Nature Biotechnology 2000, 225-227. 26. Electroactive Polymer Electrochemistry: Part 2: Methods and Applications. Plenum Press: New York, 1996. 24 CHAPTER TWO PHOTOLUMINIESCENCE AND ION SENSING PROPERTIES OF A BIPYRIDYL CHROMOPHORE-MODIFIED SEMIFLUORINATED POLYMER AND ITS METALLOPOLYMR DERIVATIVES 2.1. Introduction We recently detailed the utility of a facile, metal-free synthesis27 of fluorinated aromatic vinylene ether (FAVE) polymers and subsequent extension of this protocol to incorporate periodic chromophoric subunits into FAVE backbones.28 These materials are readily processed from solutions of common organic solvents to form free-standing optical films that exhibit intense, tunable photoluminescence. We have subsequently explored the ability of chromophore-modified FAVEs to serve a dual role as recognition/response units. A series of diphenylbithiophene-derivatized polymers, for example, produced by this protocol were tested as anion indicators. A fluoride-selective 16-fold emission enhancement was achieved over other common anions when the chromophore was enchained by a rigid fluoropolymer.29 Encouraged by these early studies, we sought to expand the functionality of FAVE derivatives to other applications. One area of interest is in modifying the FAVE scaffold with metal chelating units. Polymer-supported metal complexes, particularly conducting metallopolymers, support a wide range of applications due to the synergistic combination of polymer processibility with the ion transport and redox properties of transition metals.30-34 Metal ions can also be used to control polymer 25 morphology, providing coordinative crosslinks and templating ordered network formation or other supramolecular structures.30, 32, 35-44 Fluorinated variations of metallopolymers could maintain and augment these advantages with impressive thermal stability and resistance to atmospheric moisture typical of classical fluoropolymers. The validity of this strategy is reflected by the improved thermal stability of a NLO-active Ru(bipyridine)3 complex upon incorporation into a semifluorinated polyimide host.45 There have also been extensive studies on bipyridine-transition metal complexes immobilized within fluoropolymer membranes, particularly Nafion, for indicators, electrode materials and fuel cell applications. 46-59 Because most of these systems do not employ covalent attachment of the metal complexes to the polymer backbone, phase separation and boundary effects can be barriers to their utility. Bipyridine is the most widely used ligand in coordination chemistry due to its ability to chelate a wide variety of transition and lanthanide elements,60 and it has the added benefit of superior redox stability and facile synthetic modification. Consequently, bipyridyl units are privileged ligands for incorporation into metallopolymers. In the current case, chromophore-appended bipyridyl units were selected for incorporation into the FAVE scaffold to provide a convenient spectroscopic probe for metal coordination via absorption and photoluminescence spectroscopy. Chromophore derivatized 2,2‟-bipyridines have well-established ionophoric responses to transition metals.44, 61-73 Small molecule examples have been employed as fluorescent chemoindicators for zinc,63, 74 and bipyridyl-derivatized π- 26 conjugated polymers and conducting metallopolymers have been used in a variety of applications, particularly as indicators.33, 44, 69, 71-73, 75-85 Covalent attachment of bipyridyl units to the polymer precludes phase separation and leaching of metal complexes from the polymer over time. Herein we report the preparation and characterization of a FAVE incorporating bipyridyl chromophores and application of this polymer for colorimetric and fluorescent detection of metal ions and anions. 2.2 Results and Disscussions Polymer P1 was readily prepared in 58% isolated yield by step-growth condensation of 5,5‟-bis(4-hydroxystyryl)-2,2‟-bipyridyl and commercially available 2,2‟-bis(4-hydroxyphenyl)hexafluoropropane (6F bisphenol-A) and 4,4‟- bis(trifluorovinyloxy)biphenyl86 (Scheme 2.1). GPC analysis showed a monomodal distribution and moderate molecular weight (Mn = 22800, Mw/Mn = 2.8). Proton and 19 F NMR spectral analyses indicate 73% -FC=CF- and 27% -CH(F)–CF2- linkers (R1, Scheme 2.1) and 2% bipyridine monomer composition. Pale yellow P1 is intensely photoluminescent in the solid state or solution under UV irradiation (em = 426 nm, with a quantum yield () of 0.49(0.06) (average of seven independent determinations) with ex = 370 nm in THF) and is soluble in common organic solvents such as chloroform, dichloromethane, THF, and DMSO. 27 Scheme 2.1. Synthesis and structure of P1. When R1 = -CH(F)–CF2-, the CF2 end is uniformly directed towards the base of the R1 triangles. The CF=CF units are present as a 45:55 mixture of E- and Z- configurations. Although this work focuses on the behavior of P1 in solution, it is worth noting that P1 can be spin or drop cast to form high quality, free-standing transparent films that retain the high luminescence of the initially precipitated sample. One of the main attractive features of fluoropolymers is their high thermal stability. The thermal robustness of P1 was confirmed by DSC analysis (Tg = 92 °C) and TGA, with Td = 420 °C (at 10 wt % loss) in nitrogen and 426 °C in air. Even without protection under an inert nitrogen environment, these values are well above the operation temperature 28 of thin film devices and are markedly higher than common fluorine-free organic polymers in air. The response of P1 to an excess (20 equiv) of metal ions in solution was examined by absorption spectroscopy (Figure 2.1a). Metal-free P1 exhibits max at 368 nm, and the absorption spectrum is not significantly impacted by alkali or alkali earth metals (Na+, K+, Mg2+, or Ca2+). Transition and lanthanide ions, however, induced a notable bathochromic shift of up to 32 nm in max, the largest shift being 2+ observed for Cu (max = 400 nm). The observation of this type of ionochromic behavior, well known for small molecule bipyridine derivatives,63, 74 suggests that bipyridyl units in P1 exhibit chelation-induced electronic and geometric perturbations similar to those of polymer-free analogues. To determine whether incorporation into the FAVE polymer had altered the affinity of bipyridine units for metal ions, we 2+ determined the dissociation constant (Kd, Table 2.1) of the P1-Zn complex from a spectroscopic titration (Figure 1b; Kd was derived using a modification of the Benesi- 87 –7 Hildebrand method ). The Kd determined for P1 (5.8×10 M) is within an order of magnitude of that for unmodified 2,2‟-bipyridine under identical conditions (4.6×10–6 M), indicating that P1 binds slightly more strongly to Zn2+ than does 2,2‟-bipyridine and further confirming that incorporation into the polymer does not compromise ligating ability. The somewhat higher affinity of metals for P1 versus 2,2‟-bipyridine is anticipated because of the electron-releasing p-aryloxystyryl substituents88-90 at the 5 and 5‟ positions of bipyridyl units in the polymer. Although bipyridine-substituted polymers sometimes become insoluble upon metallation due to the formation of 29 a) 0.6 + + 2+ 2+ 0.5 } P1, Na , K , Mg , Ca 0.4 0.3 Zn2+, Cd2+, Hg2+ 0.2 Absorbance 0.1 0 300 350 400 450 500 Wavelength (nm) P1 +Na(I) +K(I) +Mg(II) +Ca(II) +Eu(II) +Co(II) +Ni(II) +Cu(II) +Zn(II) +Cd(II) +Hg(II) b) +Zn(II) 0.4 +Zn(II) 0.3 0.2 Absorbance 0.1 0 300 350 400 450 500 Wavelength (nm) Figure 2.1 a) Absorption spectra for P1 alone (initial concentration of 3.0 x 10-5 M) and in the presence of 20 equiv of the indicated metal ions in THF. b) Progressive changes in -5 the absorption spectrum of P1 (initial concentration of 3.0 x 10 M) as Zn(ClO4)2 is added (as 2.25 x 10-6 L aliquots of 2.0 x 10-3 M solution) in THF. Spectra are corrected to account for the dilution factor. 30 coordination crosslinking,44, 71 there is no evidence of precipitation upon metallation of P1, presumably due to the low percentage of bipyridyl units and favorable solubility of the fluoropolymer backbone. Ion Kd I/Io I/Io max M) ex = 370 nm) ex = 420 nm) (nm) Co2+ 6.6 0.02 0.24 394 Cu2+ 33 0.01 0.22 400 Zn2+ 0.58 0.20 9.3 390 Cd2+ 9.5 0.52 1.1 390 Hg2+ 24 0.35 3.7 390 Table 2.1. Dissociation constants and photoluminescent quenching characteristics of P1 with selected transition metal ions in THF. Data are normalized so that I/Io = 1 for P1. I and Io represent integrated emission intensity before and after addition of metal ions, respectively. Details are provided in the Experimental Section, and photoluminescence spectra for individual quenching experiments are provided in the (Appendix B2-5). The impact of excess (20 equiv) metal ions on P1 photoluminescence was investigated. Two excitation wavelengths were selected for this study: one near max for metal-free P1 (370 nm) and another near max of bathochromically shifted transition metal-P1 complexes (420 nm). Metal-free P1 has little absorbance at the later wavelength, so only emission from the Mn+-P1 complex will be observed. The relative integrated emission intensities (380-730 when ex = 370 nm or 430-830 nm when ex = 420) of P1 with select metal ions upon excitation at both wavelengths are provided in Table 2.1. Interestingly, an increase in integrated emission intensity, 31 accompanied by a 44 nm bathochromic shift of em to 468 nm, was observed only upon addition of divalent d10 metal ions with excitation at 420 nm, with Zn2+ ions initiating a significantly greater (10-fold increase) enhancement than any other ions. Complexes of d10 ions have a filled d-shell and are often emissive, though their analogues with partially filled d shells often are not. Complexes of the heavier divalent d10 ions, Cd2+ and Hg2+, also tend to exhibit lowered emission relative to their Zn2+ analogues due to the “heavy ion effect”.91 The uniquely emissive nature of Zn2+ complexes has been exploited in the design of emission turn-on chemosensors for Zn2+, including recently reported small molecules comprising chromophore- modified bipyridine derivatives.63, 74 Fluorescent titrations of P1 with select transition metals were undertaken and dissociation constants were determined from these data (Table 2.1). Fluorescence spectra for the titration of P1 with Zn2+ are provided in Figure 2.2 and spectra for the other ions in Table 2.1 are provided in the Appendix B- 1. The 10-fold increase in integrated emission exhibited by P1 is in the range of commercially-available92 fluorescent indicators for Zn2+,93-97 suggesting that, although P1 is not water soluble, this system may be practically applicable in other contexts. Many chromophore-modified macromolecular ligand scaffolds have been studied for metal ion detection; however, in some cases the emission response of fluorescent metallopolymers has shown a dependence on counteranions.66, 72, 98 A recent theoretical study notes that the extent of interaction between anion and metal dictates the magnitude of the observed ionochromic response in chromophore- 32 600 +Zn(II) 500 400 300 200 Relative Intensity Relative 100 0 430 480 530 580 630 Wavelength (nm) Figure 2.2 Progressive changes in the fluorescence spectrum of P1 (initial concentration -6 of initial concentration of 1.5×10 M) as a total of 1 equiv Zn(ClO4)2 is added (ex = 420 nm in THF). The lowest intensity spectrum is for P1 alone. derivatized bipyridyls.62 If counteranion effects are significant, the resultant optical perturbations could be utilized for anion detection. In light of these well-known anion effects, it is surprising that metallopolymers have not been more aggressively investigated as anion indicators. We therefore explored counteranion effects on the ionochromic response of P1 by adding exogenous anions (as tetrabutylammonium salts) to P1 premetallated with Zn(ClO4)2 or Cu(ClO4)2. Noncoordinating perchlorate anions were selected for initial metallation to maximize the potential for strong interaction between metal and added anions. We initially screened eight common – – – – – – 3– – anions (F , Cl , Br , I , CN , HSO4 , PO4 and O2CCH3, all added as tetrabutylammonium salts) by monitoring addition of excess anion (up to 10 equiv) by 33 absorption and fluorescence spectroscopy. Only F– and CN– produced notable changes. This is perhaps not surprising in light of the well known use of CN – as a masking agent in complexometric analysis, and the generally diminished solubility of metal fluorides.99-102 Most complexometric studies have been carried out in aqueous solution; however, recent studies related to the current work have been reported in both aqueous and organic solutions. For example, displacement of quenching Cu 2+ ions from a fluorogenic ligand in aqueous buffer has been applied in a ratiometric metal ion sensing strategy,103 and a variety of indicator displacement assays for anions rely on fluorogenic or colorimetric changes resulting from displacement of fluoro/chromophores from metal ions in a variety of solvent systems. 104-107 Of the anions screened, the Zn2+-P1 complex only responded to fluoride. Both absorption and emission spectra returned to those observed for metal-free P1 as up to – 10 equiv of F were added (Figure 2.3a-b). The marked shift in max and em in response to F– makes the Zn2+-P1 complex an ideal candidate for use as a ratiometric indicator. Ratiometric fluorescence indicators are among the best for accurate quantification of analyte concentration.108-112 In the current example, [F–] can be determined using the calibration curve (Figure 2.3c) obtained by plotting the ratio of emission intensities at 426 nm and 478 nm versus [F–]. The calibration curve maintains linearity within the micromolar concentration range and suggests an estimated lower detection limit of 6.0 × 10-7 M (11 ppb). 34 a) 0.5 +F– 0.4 +F– 0.3 0.2 Absorbance 0.1 0 300 350 400 450 500 Wavelength (nm) b) 300 +F– 250 200 +F– 150 100 Relative IntensityRelative 50 0 380 430 480 530 580 630 Wavelength (nm) c) 2.5 2 1.5 478 / I I / 426 426 1 I I 0.5 0 0.E+00 1.E-06 2.E-06 3.E-06 4.E-06 5.E-06 6.E-06 [F–] Figure 2.3 Changes in absorption (a, initial Zn2+-P1 concentration of 2.0×10-5 M; 35 spectra are corrected to account for the dilution factor.) and fluorescence (ex = 370 nm, initial Zn2+-P1 concentration of 1.5×10-6 M) (b) spectra of the Zn2+-P1 complex as tetrabutylammonium fluoride (TBAF) concentration is varied from 0 to 3×10 -5 M, and calibration curve for determining [F–] from the ratio of intensity (I) at 426 nm to that at 478 nm (c). All spectra were measured in THF. Another anion detection strategy we explored was to displace a strongly quenching metal ion from the fluorescent polymer with the aim of restoring emission. For this purpose we selected the Cu2+-P1 complex because Cu2+ is the most efficient emission quencher with ex = 370 nm. Remarkable emission enhancement was observed upon addition of 30 M fluoride (≥100-fold, Figure 2.4a) or cyanide (≥100- fold, Figure 2.4b) to the metallopolymer, while none of the other anions screened elicited a notable response. Facile methods for colorimetric and fluorescence-based detection of fluoride and cyanide have been aggressively pursued recently due to their biological/toxicological activity.113-128 These anions are produced upon hydrolysis of G agents, a subclass of organophosphorus nerve agents comprising three of the seven globally stockpiled chemical warfare agents. Hydrolysis of Sarin and Soman producefluoride, and Tabun hydrolysis yields cyanide.129 The high selectivity of Cu2+- P1 for these specific hydrolysis products could be harnessed to provide facile G-agent detection. A related strategy involving metal ion decoordination from nitrogen donor 36 a) 250 +F– 200 150 100 Relative Intensity Relative 50 0 380 430 480 530 580 630 Wavelength (nm) b) 300 +CN– 250 200 150 100 Relative IntensityRelative 50 0 380 430 480 530 580 630 Wavelength (nm) Figure 2.4 Changes in fluorescence spectrum of Cu2+-P1 complex as up to 3×10-5 M TBAF (a) or TBACN (b) are added (ex = 370 nm) in THF. ligands has recently shown promise for emission turn-on detection of nerve agent simulants.130 37 2.3. Conclusions We have extended a facile metal-free protocol for the preparation of FAVEs to prepare a 2,2‟-bipyridyl chromophore-modified variation (P1) that serves as an effective macromolecular metal ligating scaffold. P1 exhibits a strong ionochromic response to metal ions, including a highly selective 10-fold turn-on fluorescence response to Zn2+ ions. The Zn2+-P1 metallopolymer is an effective ratiometric fluorescent indicator for fluoride, while the Cu2+-P1 metallopolymer affords a highly- responsive turn-on fluorescence response to fluoride or cyanide. Extension of the synthetic route used herein to prepare additional metal-chelating FAVEs, as well as application of P1 derivatives in thin film and handheld decvices are currently underway. Experimental Materials and Characterization Methods. All reagents were obtained from Tetramer Technologies, LLC, Aldrich Chemical Co., TCI America, Alfa Aesar, Fischer Scientific, Mallinckrodt, Baker and Adamson, or MP Biomedicals, LLC and used as received. NMR spectra were recorded on a JEOL Eclipse+ 300 or Bruker Avance 300 spectrometer and chemical shifts are reported in parts per million ( ppm). 1H NMR was internally referenced to tetramethylsilane ( 0.0) or residual solvent signal, 13C NMR chemical shifts were reported relative to peak for 19 DMSO, and F NMR was referenced to CFCl3. Gel permeation chromatography (GPC) data were collected using polystyrene as a standard (Polymer Labs Easical PS-2) using a Waters 2695 Alliance System eluted sequentially through Polymer Labs PLGel 5 mm 38 Mixed-D and Mixed-E columns at 35 °C, with absorption detection for samples in CHCl3. 4,4'-([2,2'-bipyridine]-5,5'-diyldi-2,1-ethenediyl)bisphenol (1). 131 Lithium ethoxide (1 M in ethanol, 2.42 mL, 2.42 mmol) was added dropwise to a stirred solution of 5,5‟-bis(bromotriphenylphosphoniummethyl)-2,2‟-bipyridine71 (1.00 g, 1.15 mmol) and 4-(tert-butyldimethylsiloxy)benzaldehyde132 (0.575 g, 2.42 mmol) dissolved in CH2Cl2 (60 mL) at room temperature. After 4 h, the reaction mixture was poured into an equal volume of H2O. The organic layer was separated and the aqueous layer was extracted with CH2Cl2 (2 20 mL). Combined organic layers were washed with deionised water (2 50 mL), dried (MgSO4), filtered, and concentrated under vacuum. The crude product and p-toluenesulphonic acid (0.100 g) were dissolved in toluene (50 mL) and the reaction mixture was heated to reflux. After 24 h, a brick red solid precipitated. The solid was collected by vacuum filtration and washed sequentially with H2O (2 100 mL), methanol (2 100 mL), and hexanes (2 100 mL). The solid was then dried under vacuum to afford the title compound as a brick red solid (270 mg, 60%). Note: p-toluenesulphonic acid serves a dual role, isomerising the crude mixture of (E)- and (Z)-isomers to the (E)-isomer,69 and quantitatively deprotecting the hydroxyl 1 groups to afford the titled compound. H NMR (DMSO-d6, 300 MHz) δ 8.81 (s, 2H, - OH)), 8.42 (d, J = 7.89 Hz, 2H), 8.27 (d, J = 7.89 Hz, 2H), 7.467.39 (m, 6H), 7.157.06 13 (m, 4H), 6.77 (d, J = 7.89 Hz, 4H); C NMR (DMSO-d6, 76 MHz) δ 158.7, 146.8, 135.3, 132.8, 129.0, 128.6, 128.1, 126.0, 122.0, 121.0, 116.3. 39 Sythesis of P1. 5,5‟-bis(4-hydroxystyryl)-2,2‟-bipyridine (0.055 g, 0.14 mmol) and 2,2-bis(4- hydroxyphenyl)hexafluoropropane86 (0.437 g, 1.30 mmol) dissolved in anhydrous DMF (2 mL) were added dropwise to a stirred suspension of NaH (0.070 g, 2.92 mmol) in DMF (2 mL) at room temperature, and stirred for 1 h. 4,4‟-Bis(4- trifluorovinyloxy)biphenyl (0.500 g, 1.44 mmol) in anhydrous DMF (2 mL) was transferred into the solution via syringe in a single portion. The flask was then placed in a preheated oil bath at 80 °C. After 4 h at this temperature, the solution contents were precipitated into H2O, filtered under vacuum, and washed sequentially with deionized H2O (2 × 100 mL), methanol (2 × 100 mL), and hexanes (2 × 100 mL). The solid polymer was dried in a vacuum oven at 60 °C for 24 h. Additional purification was performed by dissolving the dried polymer in a minimal amount of THF and precipitated in deionized water, filtering, and washing sequentially with methanol (2 × 100 mL) and hexanes (2 × 100 mL). The solid polymer was then dried in a vacuum oven at 60 °C for an additional 24 h to afford the polymer as a pale-yellow fibrous solid (0.580 g, 58%). 1H NMR (DMSO-d6, 300 MHz) δ 8.40–8.35 (m), 8.20–8.15 (m), 7.80–7.60 (m), 7.507.27 19 (m), 6.84 (broad dt, J = 58.4 Hz, CHFCF2); F NMR (DMSO-d6, 283 MHz) δ –63.3 (s, C(CF3)2), –85.2 (d, Jab = 144.8 Hz, CHFCF2), 120.8 and 122.5 (d, J = 39.6 Hz, (Z)- CF=CF), –127.2 and 129.2 (d, J = 108.6 Hz, (E)-CF=CF), –141.2 (d, J = 59.2 Hz, CHFCF2). GPC in CHCl3 relative to polystyrene gave a monomodal distribution of Mn = 22800 (Mw/Mn = 2.8). DSC analysis of second heating at 10 °C/min to 200 °C gave Tg = 92 °C and TGA (10 °C/ min) gave Td (at 10 wt % loss) = 420 °C in nitrogen and 426 °C 40 in air. Anal. calcd for C30.98H17.44N0.04O4F11.28 (using the monomer ratios reported in Scheme 1): C, 55.66; H, 2.63; N, 0.08. Found: C, 55.36; H, 2.96; N, 0.24. General Spectroscopic Methods. Photoluminescence (PL) spectra were acquired on a Varian Cary Eclipse fluorescence spectrophotometer. Absorption spectra were recorded on a Varian Cary 50 Bio absorption spectrophotometer. Samples for all absorbance and PL spectra used tetrahydrofuran (THF) as solvent in Spectrosil quartz cuvettes having a path length of 1 cm. Initial solutions for PL analysis were filtered through 0.2 µm PTFE syringe filters prior to analysis. The THF solvent for all optical measurements was purified and made anhydrous/anaerobic by passage through alumina columns under a N2 atmosphere employing an MBraun solvent purification system. Photoluminescence quantum yields were measured relative to quinine bisulfate ( = 0.564) in 0.1 N aqueous sulfuric acid.133 Polymer concentrations are reported as moles of bipyridyl monomer unit per L. Metal salts used for ion screening were Co(NO3)2·6H2O, NiSO4·6H2O, Cu(ClO4)2·6H2O, Zn(ClO4)2·6H2O, Cd(ClO4)2·6H2O, K(PF6), Na(PF6), Mg(SO4), CaCl2, Eu(NO3)3, [Cu(NCMe)4][BF4], Hg(O2CCF3)2, and Fe(OTf)2. CAUTION: perchlorate salts are potentially explosive and should only be handled in small quantities by trained personnel who are familiar with their hazards. Metal ion selectivity of P1. A 3.0 mL aliquot of 3 × 10-5 M P1 was added to a cuvette. 4.5 × 10-4 L of 2.0 × 10-2 M metal (20 equiv) was added to the polymer solution. Absorbance changes were 41 observed for transitional metals. The experiment was repeated and followed by PL spectroscopy using 3.0 × 10-7 M P1 and a 5.0 × 10-7 L aliquot of the metal ion solution. Absorption titration of polymer with metal ions. A 3.0 mL aliquot of the 3 × 10-5 M polymer in THF solution was added to a cuvette. Aliquots (2.25 × 10-6 L) of 2.0 × 10-3 M metal ion solution were added to the polymer solution and changes were followed by collecting a absorption spectrum after each addition. PL titration of polymer with metal ions. Same as for absorption titration, but using 3.0 × 10-6 M P1, and followed by photoluminescence with ex = 370 or 420 nm. Displacement test of anions to metal in M2+-P1 complexes (M2+ = Zn2+ or Cu2+). A 3.0 mL aliquot of the 3.0 × 10-6 M P1 was added to a cuvette, followed by 4.5 × -6 -3 10 L of 2.0 × 10 M Zn(ClO4)2 or Cu(ClO4)2 and collection of an initial emission -6 -2 spectrum. A 0.45 × 10 L aliquot of 2.0 × 10 M anion solution (Fˉ, Clˉ, Brˉ, Iˉ, HSO4ˉ, 3 PO4 ˉ, or ˉO2CCH3, as tetrabutylammonium salts) was then added to the cell and another emission spectrum collected. Fluorescence Titration of M2+-P1 (M = Zn2+ or Cu2+) with anions. -6 A 3.0 mL aliquot of 1.5 × 10 M P1 in THF was added to a quartz cell. 2.25 × -6 -3 10 L (1 equiv) of 2.0 × 10 M Zn(ClO4)2 or Cu(ClO4)2 solution was added to the cuvette to make M2+-P1. Both Zn2+-P1 and Cu2+-P1 complexes were titrated by addition of 11 × 10-6 L (0.5 equiv) aliquots of 2.0 × 10-4 M tetrabutylammonium fluoride. The titration was followed by PL spectroscopy up to addition of ten equiv of anion. The Cu2+- 42 P1 complex was titrated with tetrabutylammonium cyanide solution in identical fashion. The excitation wavelength was 370 nm for these titrations. Absorption titration of Zn2+-P1 with Fˉ. As described for Fluorescence titration, but using 2.0 × 10-5 M Zn2+-P1 and 1.5 × 10-6 L (0.5 equiv) of 2.0 × 10-2 M tetrabutylammonium fluoride and following titration by absorption spectroscopy. Fluorescence titration of CNˉ with Cu2+-P1 in THF from 0.5 equiv to 10 equiv. -6 A 3.0 mL aliquot of the 1.5 ×10 M P1 in THF solution was added to a cuvette. -6 -3 A 2.25 × 10 L (1 equiv) aliquot of 2.0 × 10 M Cu(ClO4)2 solution was added to the cuvette to generate Cu2+-P1. 11 × 10-6 L (0.5 equiv) of the 2.0 × 10-4 M CNˉ in THF 2+ solution was added to the Cu -P1 solution after each scan (ex = 370 nm) until a total of ten equiv CN– had been added. 43 REFERENCES CITED 1. Iacono, S. T.; Budy, S. M.; Ewald, D.; Smith, D. W., Jr., Chemical Communications (Cambridge, United Kingdom) 2006, 4844-4846. 2. Iacono, S. T.; Budy, S. M.; Moody, J. D.; Smith, R. C.; Dennis W. Smith, J., Macromolecules, 2008, 41, 7490-7496. 3. Gilliard, R. J.; Iacono, S. T.; Budy, S. M.; Moody, J. D.; Smith, D. 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Introduction Organic semiconductors such as -conjugated polymers (CPs, Chart 1A) have been targeted as active components of optoelectronic devices due to their processability, tunability from UV- to IR-range light absorption / emission, and potential for metal-like conductivity in their doped states.134-136 These spectacular properties have led to the use of CPs in applications ranging from thin film solar cells137, 138 and organic light-emitting diodes (OLEDs)139 to printable circuits and batteries.140 Conducting metallopolymers (CMPs) are CPs that incorporate metal ions or atoms into them, either as integral backbone components or in sidechains.141, 142 Including metal ions can augment the already impressive property profile of CPs because metals can endow CMPs with a richer range of bonding geometries, magnetic properties, redox Figure 3.1. Schematic illustrating how insoluble network formation (left) can be prevented by the steric coordination control strategy (right). 53 Chart 3.1. CPs (A) and Bipy-Derivatized CPs (B) A) B) 54 Chart 3.2. Materials Featuring Sterically Enshrouded 2,2’-Bipyridyl Units chemistry and photochemistry than may be possible from organic CPs alone. One area in which CMPs have proven especially successful is in OLEDs. Heavy atoms like transition metals can improve the efficiency of phosphorescence (emission from the triplet excited 55 state) via spin orbit coupling. Because up to75% of excited states generated in electroluminescent devices are triplets, efficient phosphorescence could lead to up to four times the efficiency of devices that would otherwise rely on fluorescence for light emission.143-145 The majority of studies on phosphorescent CMPs for OLEDs to date have focused on Ir- and Pt-containing CMPs. Although a wide range of ligands have been used to bind metals in CMPs, 2,2‟- bipyridyl (bipy) derivatives are among the most common (Chart 3.1B). This is presumably because of their relatively facile functionalization, stability and ability to bind a large number of transition and lanthanide elements.146 The versatility of the bipyridyl scaffold has consequently found extensive use in materials and supramolecular chemistry.147 The belwether study by Wang and Wasielewski69 demonstrated the effect of a variety of metal ions on the photophysical properties of bipy-modified CPs, including the effect of CP spacer length between bipy units. Bipy-modified CMPs have since found application in conjugated polymetallorotaxanes,148-156 electroluminescent devices, organic solar cells, and as chemical sensors.61, 71, 73, 157, 158 When one attempts to prepare CMPs by metallating a bipy-functionalized CP, multiple bipy units can bind to some metal ions. The result is coordinative crosslink formation (Figure 3.1, left)44 and consequent production of a highly insoluble network solid. The loss of solubility leads not only to diminished capacity for processing the materials for devices, but also to a loss of the ability to carry out solution characterization. The coordination chemistry of bipy derivatives can be controlled by the use of bulky substituents. Such strategic distribution of sterically encumbering units to control 56 coordination has found widespread utility in supramolecular and materials chemistry,159, 160 and has been exploited in the rational design of elegant bipy-scaffolded supramolecular assemblies.161-163 We recently reported that distribution of bulky mesityl groups about a bipy binding site similarly provides steric coordination control in a -conjugated small molecule model (TAB, Chart 3.2)74 and in a bipy modified poly(p-phenylene vinylene) derivative (PPV1, Chart 3.2).164 The sterically enshrouded metal coordination sites enforce a 1:1 metal:bipy binding ratio (Figure 3.1, right), leading to impressive improvements in the solubility / processability of metallated polymers versus coordinatively-crosslinked polymers that result upon metallation of non-sterically encumbered analogues. Furthermore, PPV1 bound a variety of transition elements with attendant changes in photophysical properties. In the current work, we report copolymers of polyfluorene and poly(p-phenylene ethynylene) (PPE) derivatives incorporating different ratios of sterically-enshrouded bipy monomer units in their backbones. The photophysical and electrochemical properties of select polymers, metal-free and metallated, are reported. 3.2 Results and Discussion Design and Synthesis Our first attempt of utilizing the steric protection control to maintain the solubility integrity of metallopolymers was the synthesis of CMP1 via Horner-Wittig condensation. 165 CMP1 was a derivative of poly(p-phenylene vinylene) which was structurally similar 57 Scheme 3.1. Preparation of Bulky Bipy Monomers to P1 166except the lack of bulky TAB motif. TAB was first synthesized and reported by our group in 2008 for its amazing quantum efficiency (0.62) and 1:1 ligand to metal binding pattern. 167 The detail discussion of CMP1 versus P1 was presented on Macromolecules Rapid Communication. 165 Because the steric capsule about the bipy unit in TAB (Chart 3.2)74 enforces a 1:1 metal:bipy ratio in PPV1,164 we have chosen to incorporate this same motif into the polyfluorene(PF) and poly(p-phenylene ethynylene) (PPE) derivatives (Chart 3.2) for the current study. The goal was to explore how the photophysical and electrochemical properties of metal-free and metallated materials are related to the identity and length of the -conjugated spacer between ligand monomer units. Another goal was to compare the properties of the sterically encumbered materials 58 to those of previously reported materials lacking such bulk. Preparation of TAB-modified PPE and PF derivatives required a bipy-modified monomer capable of participating in Sonogashira-Hagihara or Suzuki-Miyaura type coupling, respectively. The initial monomer targeted was BrTABBr. This monomer was readily prepared in 38% yield by Horner-Wittig condensation of the m-terphenyl aldehyde 1 with bis(phosphonate ester)-modified bipy derivative 4 as shown in Scheme 3.1. Unfortunately, the degrees of polymerization for polymers produced using BrTABBr were unsatisfactory. To solve this problem, we prepared ITABI, whose aryl iodide units make it more active in Pd-catalyzed coupling compared to BrTABBr. Preparation of ITABI required a more involved synthetic approach than did BrTABBr (Scheme 3.1). Figure 3.2. ORTEP drawing (50% probability ellipsoids) of [PdCl2(BrTABBr)]. H atoms are excluded for clarity. Refinement details are provided in the Appendix C-2a,b. 59 The first step was protection of the aldehyde functionality in 1 as an acetal to give 2 (87%). This was followed by lithium-bromine exchange of 2 with n-butyl lithium, subsequent quenching with molecular iodine, and finally an acid workup to deprotect the aldehyde, giving 3 (65%). Compound 3 was then employed in a Horner-Wittig condensation with 4 to give ITABI (65%). Although spectroscopic studies had verified the 1:1 metal to ligand ratio for TAB derivatives, it was of interest to isolate and structurally characterize metal complexes in order to unequivocally demonstrate the geometry of metal binding sites available from the sterically encumbered ligand. In this vein, [PdCl2(BrTABBr)] was prepared and characterized by single crystal X-ray diffraction (Figure 3.2). Despite the global steric protection about the bipy unit, the distribution of bulky groups provides a pocket of free space about the Pd center such that a standard pseudo-square planar geometry is observed, with no apparent distortions. The average Pd–N (2.03 Å) and Pd–Cl (2.27 Å) bond lengths in [PdCl2(BrTABBr)] compare well to the Pd–N (2.02 Å) and Pd–Cl (2.29 168 Å) lengths in unencumbered [PdCl2(2,2‟-bipyridine)]. The N–Pd–N (80.95(17)°) and Cl–Pd–Cl (90.15(7)°) angles in [PdCl2(BrTABBr)] are also simlar to analogous N–Pd–N 168 (80.6(1)°) and Cl–Pd–Cl (89.94(5)°) for [PdCl2(2,2‟-bipyridine)]. Polymerization reactions employing ITABI (Scheme 3.2) produced polymers with reasonable molecular weights. A 1:1 ratio of ligand to spacer monomer was used to produce alternating copolymers PF1 and PPE1. A 1:3 ratio of ligand to spacer monomer was used to produce statistical copolymers PF3 and PPE3. These copolymers are of interest because they will reveal how properties change with three times the average 60 Scheme 3.2. Preparation of Bulky Bipy Polymers spacer length between ligating sites versus PF1 and PPE1. PF1 and PF3 were yellow to yellow-green solids, while PPE1 and PPE3 were isolated as bright yellow solids. All of the polymers are readily soluble in common polar organic solvents such as chlorobenzene, dichloromethane, chloroform, acetone and tetrahydrofuran (THF). Visually, the polymers are also brightly photoluminescent in solution upon irradiation with a handheld UV light (λmax = 365 nm). Photophysical Properties of Metal-Free Polymers Select photophysical data for PF1, PF3, PPE1, PPE3, PPV1 and some related bipy-modified CPs from the literature (Chart 3.1B) are provided in Table 3.2. The π- conjugated backbone of PF1 is identical to that in CP1c,73 the only structural difference being the presence of flanking mesityl groups as steric shields in PF1. Predictably, the absorption maxima (λmax) for the two polymers are nearly identical. A significant difference between the materials is that the Stokes shift of CP1c (83 nm) is significantly greater than that of PF1 (52 nm) so the emission maxima (λem) of CP1c (485 nm) and PF1 (452 nm) differ by 33 nm. The magnitude of a Stokes shift is related to the difference in geometry of the ground versus excited state,91, 133 so a 61 smaller Stokes shift can reflect a more rigid CP backbone and its greater resistance to geometric distortion.169-172 The sterically encumbering groups in PF1 are likely to diminish the conformational flexibility of PF1 and may thus be the origin of the smaller Stokes shift. A comparable Stokes shift is observed in similarly encumbered PF3 (58 nm), although its λmax is shifted to the blue by ~10 nm versus CP1c or PF1 because fluorenylene units comprise a higher percentage of the polymer chain in PF3. The photoluminescence quantum efficiency (Ф) of PF1 (0.49) and CP1c (0.44) are identical within error, whereas that of PF3 (0.62) is significantly higher, suggesting that incorporation of bipy units into the backbone leads to the diminished photoluminescence efficiency. The -conjugated backbone of PPE1 is identical to that in CP1b, the only structural difference being the mesityl groups in PPE1. The absorption maxima (λmax) for the two polymers differ by about 20 nm, though, in contrast to the polyfluorene derivatives, the Stokes shift for sterically encumbered PPE1 (51 nm) and PPE2 (52 nm) are nearly identical to unencumbered CP1b (50 nm), and Ф is slightly higher for CP1b (0.41) versus PPE1 (0.32) and PPE3 (0.32). As noted previously,73 the difference in how incorporating bipy units influences the properties of PF versus PPE derivatives stems from the difference in energy matching between the spacer and the bipy unit. The 2,5- dialkoxyphenyleneethynylene units in the PPE derivatives are significantly more electron rich than are the 7,7-dialkylfluorenylene units in PF derivatives, leading to a poorer energy match between the spacer and the metal-binding subunits of the polymer. Such considerations regarding energy matching between the conjugated system and the 62 embedded metal complex141 are another motivation for determining relative orbital energies by electrochemical measurements, as will be discussed further in the following sections. The three PPV derivatives listed in Table 3.1 all feature the same -conjugated backbone, but each has a different number of hexyloxy sidechains, and PPV1 features bulky mesityl substituents. Alkoxy-substituted PPV derivatives exhibit bathochromically shifted absorption and emission versus derivatives lacking such electron donating Table 3.1. Select Photophysical Properties of Polymers 63 173 substituents. Similarly, the λmax values for PPV derivatives in Table 3.2 predictably increase as the number of electron-releasing hexyloxy substituents increases from PPV1 (437 nm) to CP2a (449 nm)174 to CP1a (462 nm). The Ф values for PPV derivative (0.30- 0.37) are similar to one another and to those of the PPE derivatives discussed above (0.32-0.42). The Stokes shift of PPV derivatives are also similar to one another (66-78 nm) but somewhat higher than those of PPE derivatives (50-52 nm), reflecting the additional conformational flexibility afforded by the double bonds in PPV derivatives versus triple bonds in PPE derivatives. The influence of the spacer on photophysical properties is apparent upon comparison of absorption and emission maxima. The general trend that emerges is that the absorption and emission maxima are progressively red shifted upon changing from PF to PPE to PPV-based spacers. This is not surprising because the same trend is observed for photophysical parameters of the bipy-free parent polymers comprised of 7,7-dialky- 2,7-fluorenylene, 2,5-dialkoxyphenyleneethynylene, or 2,5-dialkoxyphenylenevinylene repeat units. Photophysical Response of Polymers to Metal Ion Coordination Previous work with TAB and PPV1 confirmed that the dissociation constants measured for metals such as Cu2+, Fe3+ and Zn2+ are essentially the same affinity as they are for simple 2,2‟-bipyridyl.74 Job analysis derived from titrations followed by absorption and photoluminescence spectroscopy confirmed the 1:1 metal:bipy binding mode, and the results of a single crystal X-ray diffraction structure determination of [PdCl2(BrTABBr)] (Figure 3.2) demonstrate the ability of the core to shield the metal- 64 PPE1 A) PPE1 0.4 120 0.3 Zn2+ 80 Cd2+ 0.2 Hg2+,Cd2+,Cu2+ Intensity Hg2+,Co2+,Zn2+,Cu2+ Co2+ 40 Absorbance Absorbance 0.1 0 0 285 385 485 585 425 475 525 575 625 Wavelengths (nm) Wavelength (nm) PPE-Bipyno metal +Cd +Co PPE-Bipyno metal +Cu +Co +Cu +Hg +Zn +Zn +Hg +Cd B) 0.27 PF PF 600 2+ Hg2+ Zn 0.18 2+ 2+ 2+ 2+ Cd ,Co ,Zn ,Cu 400 Hg2+ Intensity 0.09 Co2+ Absorbance 200 Cd2+,Cu2+ 0 0 300 350 400 450 500 550 425 475 525 575 625 Wavelength (nm) Wavelength (nm) PF-Bipyno metal alone Hg Co PF-Bipyno metal alone +Hg +Zn Cd Zn Cu +Cu +Co +Cd Figure 3.3. Absorption (left) and photoluminescence (right) responses of PF1 (A) and PPE1 (B) to addition of metal ions. bound -conjugated construct from external - interactions or coordinative crosslinks. In the current study, the photophysical response of the polymers to select metal ion coordination was examined by absorption and photoluminescence spectroscopy. The spectroscopic changes observed upon excess metal ion (10-20 equiv) addition to PF1 and PPE1 are provided in Figure 3.3. Corresponding data for PF3 and PPE3 were similar, and their spectra are thus provided in the Supporting Information. Titrations of each polymer with each metal ion were also carried out and followed by both absorption and 65 photoluminescence spectroscopy in order to observe the gradual change of the spectra as up to one equiv of each metal ion was added. The effects of excess metal ion addition on absorption and emission properties are summarized in Table 3.2, while spectra for all titrations are provided in the Appendix B37-84. Confirmation that the metal ions are binding to the bipy sites in the polymers is provided by observed red-shift in absorbtion maxima for all of the polymers with all of the metals listed in Table 3.2. A similar effect was noted for TAB. The manner in which different metals impact photoluminescence varies. One observation that applies generally to all of the polymers in Table 3.2, though, is that they exhibit significantly less photoluminescence quenching upon binding the diamagnetic Zn2+, Cd2+ and Hg2+ ions, all of which have a closed-shell d10 electronic configuration, compared to Co2+ and Cu2+, both of which have only partially-filled d electron shells. This is similar to the trend observed for small molecule model TAB74 as well as related bipy-modified CPs.69, 71, 73, 158 The trends in photoluminescence quenching efficacy induced by binding are quite different for Cu2+ versus Co2+. First, Cu2+ induces a greater quenching effect the more electron deficient the polymer host; PF > PPE > PPV. The Co2+ induced quenching follows the opposite trend, with the greatest quenching for the most electron rich polymer host, PPV1. With this trend in mind, it is not surprising that the presence of a greater percentage of electron-withdrawing bipyridyl units in PF1 / PPE1 leads to greater Cu2+ induced quenching of either of these versus their less bipy-laden analogues PF3 and PPE3, respectively. Predictably, then, Co2+ induces greater quenching in PF3 and PPE3 66 versus more electron deficient PF1 or PPE1, respectively. The origin of this disparity is not entirely certain, but we hypothesize that is is linked to the fact that Cu2+ is in its highest readily-accessible oxidation state under the experimental conditions employed, while Co2+ can attain a Co3+ oxidation state through release of an electron to the ligand host. In fact, a potential metal to ligand charge transfer (MLCT) band can be seen in the absorption spectrum of the PF1-Co2+ complex in Figure 3.2A (left), but not in the absorption spectrum for the PPE1-Co2+ complex in Figure 3.2B (left). The extent to which electron transfer from metal becomes increasingly more facile as the electron deficiency of the polymer host increases. Electrochemistry of Polymers and Metallopolymers The electrochemical properties of the TAB-modified CPs along with Zn2+ and Cu2+ metallopolymer derivatives were probed by cyclic voltammetry (CV) with the aim of elucidating the HOMO (ionization energy, IE) and LUMO (electron affinity, EA) levels. Electrochemical data are summarized in Table 3.3, along with data for PFO175 (Chart 3.1A) and unmodified PPE176 for comparison. In some cases, either EA, IE or both could not be determined by CV. In these cases the band gap estimated from the onset of absorption spectra were used to fill in data where possible. Predictably, as more of the bipy-containing monomer units of metal free CPS were replaced by fluorenylene (from PF1 to PF3 to PFO) or phenyleneethynylene units (from PPE1 to PPE3 to PPE), the EA, IE and band gap all approached those of the bipy- free parent CPs. Incorporating bipy units had the effect of raising the IE closer to the vacuum level versus the IE in the bipy-free materials, and bipy incorporation had a 67 Table 3.3. Electrochemical and Band Gap Datac b Ionization energy (eV) Electron Affinity (eV) Bandgap Eg (eV) no Mn+ +Zn2+ +Cu2+ no Mn+ +Zn2+ +Cu2+ no Mn+ +Zn2+ +Cu2+ PF1 5.35 - - 2.71a - - (2.64) (2.25) (2.38) 2.56 PF3 5.42 5.16 5.10 2.86 2.70a 2.72a (2.70) (2.46) (2.38) PFO 5.80 NA NA 2.90 NA NA 2.90 NA NA PPE1 4.55 4.57 4.56 2.76 3.26 3.20 1.79 1.31 1.36 PPE3 5.12 - - 2.54a - - (2.58) (2.41) (2.38) PPE 5.90 NA NA 2.50 NA NA 3.40 NA NA a. These data are estimated using the optical bandgap b. Numbers in parentheses are bandgaps estimated from onset of absorption c. Values for ionization energies and electron affinities are quoted as values below vacuum level greater impact on the IE levels of the PPE derivatives than on those of the PF derivatives. The later observation if attributable to the fact that fluorenylene units are already significantly more electron deficient compared to the 2,5-dialkoxyphenyleneethynylene units in the PPE derivatives. The EA levels were less effected than the IE levels by incorporating bipy units, but this is not altogether surprising given that organic CPs tend to be much more readily oxidatively doped than reductively doped; incorporating bipy units does not seem to significantly alleviate this difficulty. Because the steric coordination control strategy allows CMP derivatives of our polymers to remain soluble and free of coordinative crosslinks, they were amenable to solution cyclic voltammetric studies. When PF derivatives bind metal ions, which are positively charged and thus electron-withdrawing, the effect is similar to incorporating 68 electron-withdrawing bipy units. First, and consistant with the observed red shift in absorption spectra, the band gap decreases upon metal ion binding. Metal coordination to the polymers additionally leads to raising the IE towards the vacuum level. For the PPE derivatives, the large effect of bipy incorporation remains relatively the same even after metal ions bind. The EA, however, is relatively constant for PF derivatives before and after metal binding, whereas the EA sinks lower below vacuum level in the PPE derivatives. Unfortunately, however, observations pertaining to the EA values must be viewed with caution because the EA values for metal-free and metallated polymers were only electrochemically determinable (without using less-reliable optical band gap estimation) for one polymer (PF1). Nonetheless, the data that were obtainable suggest that the family of soluble and easily metallated materials studied may have potential for independantly tuning the EA and IE to desired levels for device applications through judicious selection of polymer host and metal complex guest energy levels.141 Experimental Reagents and General Methods. Reagents were obtained from Aldrich Chemical Co., TCI America, Acros or Alfa Aesar and used without further purification. Solvents were purified by passage through alumina columns under a dry N2 atmosphere employing an MBraun solvent purification system. Air sensitive operations were carried out in an MBraun dry box or using standard 74 71 Schlenk line techniques under N2. The materials M1, P1, 5,5‟- bis(diethylphosphonylmethyl)-2,2‟-bipyridine 177 and (E),(E)-1,4-Bis(4-formyl-3,5- dimesitylstyryl)-2,5-di-n-hexyloxybenzene178 were prepared by literature procedures. 69 NMR spectra were obtained using a Bruker Avance 300 spectrometer operating at 300 MHz for protons. All spectra were collected at 25 °C and referenced to TMS or residual solvent signals. Absorption spectra were recorded using a Cary 50 spectrophotometer and photoluminescence (PL) spectra were recorded using a Varian Eclipse spectrofluorimeter. Samples for fluorescence had a path length of 1 cm in quartz cuvettes, with optical density of <0.05 in degassed anhydrous solvent, and all samples were filtered through a 0.4 µm PTFE syringe filter immediately prior to use. Quantum yield determinations were performed in triplicate and are reported, with standard deviations, relative to quinine 133 bisulfate in 0.1 N H2SO4(aq) (Ф = 0.546). General procedures for cyclic voltammetry study. Polymer was dissolved in anhydrous CH2Cl2 containing 0.1 M TBAPF6 as supporting electrolyte and 3-mm-diameter glassy carbon disk was used as the working electrode, with Pt as counter electrode and Ag as reference electrode. Ferrocene was added at the end of the experiment as internal reference for the potential. General procedures for absorption and photoluminescence spectroscopy. All reagents were used as received from the supplier without any further purification. All solvents were HPLC grade or better and were degassed using nitrogen. The tetrahydrofuran was purified by MBraun solvent purification system which was set up under nitrogen and employed alumina columns. All UV-vis data was collected using a Varian Cary-50 Bio spectrophotometer and the fluorescence data was collected using a Varian Eclipse spectrophotometer. Initial solutions for PL analysis were filtered through 0.2 µm PTFE syringe filters prior to analysis. 70 Metal ion selectivity of polymer. A 3.0 mL aliquot of each polymer in tetrahydrofuran solution was measured and added to an optical path length of 1 cm quartz cell. Excess metal ions (10 or more equiv) were added to the polymer solution. Absorbance changes were measured. The experiment was repeated and followed by PL spectroscopy. The metal salts used were Co(NO3)2·6H2O, Cu(ClO4)2·6H2O, Zn(ClO4)2·6H2O, Cd(ClO4)2·6H2O, K(PF6), Na(PF6), Mg(SO4), CaCl2, Eu(NO3)3 and Hg(O2CCF3)2. Absorption and photoluminescence titrations of polymers with metal ions. A 3.0 mL aliquot of each polymer in tetrahydrofuran solution was added to a quartz cell having an optical path length of 1 cm. Aliquots, each containing 0.1 equiv of each metal ion with respect to bipyridyl ligating units, were added to the polymer solution and an absorption or photoluminescence spectrum was collected after each addition. Synthesis of (BrTABBr). A mixture of 0.82 g (1.95 mmol) (1) and 0.40 g (0.884 mmol) (4) were dissolved with 100 mL of THF. Potassium tert-butoxide 0.218 (1.95 mmol) in 20 mL THF was dropwise added into the above solution and then stirred for 40 h. The solution was then poured into 400 mL saturated aqueous sodium bicarbonate. The product was separated by dichloromethane / water extraction. Volatiles were removed under reduced pressure. Pentane (50 mL) was slowly added to a concentrated dichloromethane solution of the 1 crude material to yield the product (0.42 g, 47%). H NMR (300 MHz, CDCl3): δ 2.01 (s, 24H), 2.36 (s, 12H), 5.80 (d, 2H), 6.55 (d, 2H), 6.97 (s, 10H), 7.09 (d, 2H ), 7.99 (m, 4H). 71 + HRMS (m/z): calc‟d for C62H59Br2N2 (M+H) 989.3045; found 989.3045. mp: 228-229 °C. Synthesis of (2). A mixture of 2.10 g (4.98 mmol) (1), 1.55 g (24.7 mmol) ethylene glycol and 0.068 g (0.399 mmol) tosic acid were dissolved with 180 mL of toluene in a flask equipped with a Dean-Stark distillation setup. The reaction was refluxed overnight, and then the solution was cooled to room temperature. Dichloromethane (25 mL) was added and the organic layer was sequentially washed with saturated sodium bicarbonate (25 mL) and brine (25 mL). The organic layer was collected and all volatiles were removed under reduced pressure, yielding a yellowish solid. The final product was obtained as a white solid (2.0 g, 87%) after washing with methanol (6 mL) and pentane (10 mL). 1H NMR (300 MHz, CDCl3): δ 2.03 (s, 12H), 2.33 (s, 6H), 2.85 (m, 2H), 3.38 (m, 2H), 13 5.31(s, 1H), 6.91 (s, 4H), 7.21 (s, 2H). C NMR (75.4 MHz, CDCl3): δ 20.8, 21.1, 64.9, 101.9, 123.3, 127.5, 132.0, 132.7, 136.4, 136.6, 136.7, 144.1. HRMS (m/z): calc‟d for + ° C27H30O2Br (M+H) 465.1429; found 465.1425. mp: 189-190 C. Synthesis of (3). Compound 2 (2.19 g, 4.71 mmol) was dissolved in 50 mL of tetrahydrofuran under nitrogen. The solution was cooled to 78 °C and 2.5 M n-butyl lithium (2.2 mL, 5.65 mmol) was added via syringe. The mixture was stirred for 1 h at 78 °C, after which time elemental iodine (2.4 g, 9.42 mmol) was added. The mixture was allowed to stir for 21 h at room temperature. Excess iodine was quenched with 30 mL saturated aqueous sodium sulfite. The organic layer was collected and 30 mL of 50 % HCl(aq) was added followed 72 by refluxing for 12 h. The solution was allowed to slowly cool to room temperature, during which time a yellow solid formed. The yellow solid was collected by filtration, washed with pentane (2×10 mL) and dried in vacuo to give the product as white solid 1 (1.44 g, 65%). H NMR (300 MHz, CDCl3): δ 2.00 (s, 12H), 2.34 (s, 6H), 6.95 (s, 2H), 13 7.59 (s, 2H;), 9.60 (s, 1H). C NMR (75.4 MHz, CDCl3): δ 20.6, 21.1, 101.2, 128.2, 132.0, 132.8, 134.8, 135.1, 137.5, 138.8, 145.2, 191.8.2768; HRMS (m/z): calc‟d for + C25H25OI (M+H) 468.0963; found 468.0951. mp: 160-161 °C. Synthesis of ITABI. A mixture of 3 (1.0 g, 2.1 mmol) and 4 (0.487 g, 0.107 mmol) was dissolved in 20 mL of THF. A solution of potassium tert-butoxide (0.35 g, 3.1 mmol) in 20 mL THF was then added dropwise followed by stirring for 40 h. About 4 mL of 20% sodium hydroxide in water were then added. After a dichloromethane / basic water extraction, the organic layer was collected and all volatiles were removed under reduced pressure. The final product was obtained by trituration with methanol (3 × 10 mL) and pentane followed by 1 drying to produce a yellow powder (0.75 g, 65%). H NMR (300 MHz, CDCl3): δ 2.01 (s, 24H; -CH3), 2.36 (s, 12H; -CH3), 5.81 (d, 2H), 6.56 (d, 2H), 6.96 (s, 4H), 7.08 (d, 2H), 13 7.48 (s, 8H), 8.00 (d, 2H). C NMR (75.4 MHz, CDCl3): δ 20.5, 21.1, 93.5, 120.4, 126.7, 128.2, 128.4, 132.9, 133.3, 133.4, 135.5, 136.8, 137.3, 137.8, 142.7, 147.6, 154.2. HRMS + ° (m/z): calc‟d for C62H59I2N2 (M+H) 1085.2768; found 1085.2788. mp: 226-227 C. Synthesis of 1,4-bis(hexyloxyl)-2,5-diiodobenzene. Synthesis of this compound followed the reported procedure.179 A mixture of 1.11 g (4.00 mmol) 1,4-bis(hexyloxy)benzene, 0.91 g (3.6 mmol) iodine , and 0.42 g (2.4 73 mmol) potassium iodate were dissolved in 1.2 mL 30% sulfuric acid, 1.6 mL CCl4 and 7 mL of acetic acid. The solution was refluxed for 3 h at 75 °C. Pink crystals were collected after cooling on ice for 30 min. The crystals were collected and further washed with methanol (4×20 mL) and dried under vacuum for 4 h to yield the product as a white 1 solid (1.19 g, 56%). H NMR (300 MHz, CDCl3): δ 0.93 (t, 6H), 1.36 (m, 8H), 1.54 (m, 4H), 1.82 (m, 4H), 3.94 (t, 4H), 7.19 (s, 2H). Synthesis of 2,7-diiodo-9,9-dihexylfluorene. Synthesis of this compound followed the reported procedure.179 A mixture of 1.0 g (2.56 mmol) 9,9-dioctyl-9H-fluorene, 0.585 g (2.30 mmol) iodine and 0.330 g (1.54 mmol) potassium iodate was mixed with 1.2 mL of 30% sulfuric acid, 1.6 mL carbon tetrachloride and 7 mL of acetic acid. The mixture was refluxed at for 48 h, then cooled to room temperature. The light yellow organic layer was collected and the crude product was precipitated by addition of 10 mL of methanol. The solvent was decanted away and the product was resissolved in 4 mL of pentane. Upon standing a white-yellow crystalline solid formed. This was collected and dried to yield the target compound (1.0 g, 60%). 1H NMR (300 MHz, CDCl3): δ 0.59 (t, 6H), 0.85 (m, 6H), 1.21 (m, 18H), 1.92 (m, 4H), 7.41 (d, 2H), 7.68 (t, 4H). Synthesis of [PdCl2(BrTABBr)]. A solution of 50 mg (0.050 mmol) of BrTABBr in 5 mL of THF was combined with 9.0 mg of PdCl2 (0.050 mmol) in 2 mL methanol and 3 mL dichloromethane. The solution mixture was refluxed for 15 h, then filtered through a 0.2 µm PTFE syringe filter. Gold yellow crystals suitable for X-ray diffraction were obtained (59 mg, 60%) by 74 1 slow diffusion of hexanes into the filtrate. H NMR (300 MHz, THF-d8): δ 2.02 (s, 24H), 2.38 (s, 12H), 5.78 (d, 2H), 6.77 (d, 2H), 7.02 (s, 8H), 7.37 (d, 6H), 7.82 (d, 2H), 8.78 (S, 13 2H). C NMR (75.4 MHz, THF-d8): δ 17.8, 18.6, 120.0, 120.6, 124.3, 126.6, 127.9, 129.7, 130.2, 132.5, 133.1, 134.2, 134.6, 135.9, 141.7, 146.9, 152.0. Anal. calc‟d for C62H58Br2Cl2N2O2Pd·2H2O: C, 61.83; H, 5.19; N, 2.33; Found: C, 61.79; H: 5.12; N: 2.35. mp: 178-179 °C. Synthesis of PF1. A mixture of 50.0 mg (0.0461 mmol) ITABI, 23.1 mg (0.0461 mmol) 9,9- dihexylfluorene-2,7-bis(trimethyeneborate), 90.0 mg (0.277 mmol) cesium carbonate and 2.1 mg (0.0021 mmol) tetrakis(triphenylphosphine)palladium were suspended in 15.0 mL of dimethylformamide. The mixture was allowed to stir for 20 h at 100 °C, then cooled to room temperature. The organic solution was extracted with 50 mL of dichloromethane, 50 mL EDTA and 50 mL brine. The organic layer was collected and concentrated to 3 mL under reduced pressure then dropwise added to 20 mL of methanol resulted in fine 1 green yellow precipitate. (30 mg, 55%) H NMR (300 MHz, CDCl3) δ 0.69-2.38 (26H), 2.12 (s, 24H), 2.42 (s, 12H), 5.85 (d, 2H), 6.74 (d, 2H), 6.98 (s, 2H ), 7.05 (8H), 7.10- 7.21 (4H), 7.54 (4H), 7.65-7.76 (4H), 8.06 (s, 2H). GPC: Mw/Mn = 15000/9000 = 1.7 Synthesis of PF3. Mixtures of 50.0 mg (0.0461 mmol) ITABI, 51.5 mg (0.0922 mmol) 9,9- dihexylfluorene-2,7 bis(trimethyleneborate), 29.6 mg (0.0461 mmol) 2,7diiodo-9,9- dioctyl-9H-fluorene, 90.0 mg (0.277 mmol) cesium carbonate and 2.1 mg (0.002 mmol) tetrakis(triphenylphosphine)palladium were dissolved with 18 mL of 75 dimethylformamide. The solution mixture was allowed to go for 18 h at 95 °C then cooled to room temperature for 2 h. The organic solution was extracted with dichloromethane (2×15 mL) and washed with EDTA (2×25 mL) and Brine (2×25 mL). The dichloromethane layer was collected and concentrated to 3 mL by reduced pressure then dropwise added to 20 mL of methanol resulted in fine green yellow precipitate that 1 was collected and dried for 18 h (51 mg, 60%) H NMR (300 MHz, CDCl3) δ 0.65-1.11, 1.98-2.39, 5.81 (d, 2H, -CH2), 6.71 (d, 2H, -CH2), 6.94-7.12, 7.50-7.81, 8.02. GPC: Mw/Mn = 25000/8000 = 3.1 Synthesis of PPE1. Mixtures of 50.0 mg (0.0433 mmol) BrTABBr, 0.33 mg (0.002 mmol) copper iodide and 2.0 mg (0.002 mmol) tetrakis(triphenylphosphine)palladium were dissolved in 5.0 mL of toluene. 13.0 mg (0.0433 mmol) 1,4-diethynyl-2,5-bis(hexyloxy)benzene in 4.0 mL of diisopropyl amine were dropwise added into above solution. Allowed the reactions to stir at room temperature for 25 h then reflux at 50 °C for 24 h. Once the solution cool down to room temperature, removed all solvent by reduced pressure was done to obtain polymer film. Dichloromethane (3 mL) was applied to dissolve the polymer film then dropwise added to 20 mL of methanol. Fine orange yellow precipitate 1 was obtained with a yield of 29 mg (60%). H NMR (300 MHz, CDCl3) δ 0.79-1.61 (22H), 2.02 (s, 24H; -CH3), 2.36 (s, 12H; -CH3), 4.01(t, 4H; -OCH2), 5.82(d, 2H; -CH2), 6.66 (t, 2H), 6.93(s, 4H ), 6.98-7.14 (6H), 7.30 (2H), 7.48 (s, 8H;), 8.01 (s, 2H). GPC: Mw/Mn = 39000/9400 = 3.6 76 Synthesis of PPE3. Mixture of 50.0 mg (0.0433 mmol) BrTABBr, 0.35 mg (0.002 mmol) copper iodide and 2.0 mg (0.002 mmol) tetrakis(triphenylphosphine)palladium were dissolved in 10 mL of toluene. To 27.8 mg (0.092 mmol) 1,4-diethynyl-2,5-bis(hexyloxy)benzene and 24.4 mg (0.046 mmol) 1,4-bis(hexyloxyl)-2,5-diiodobenzene, 5.0 mL of diisopropyl amine were used. Combination of the two solution mixture was allowed to stir at room temperature for 25 h then reflux at 80 oC for 24 h. Dichloromethane (3.0 mL) was added to redissolve the polymer film after all volatile was removed by reduced pressure. Re- precipitation of orange yellow polymer (48 mg, 65%) was achieved by dropwise addition 1 of dichloromethane solution into 20 mL of methanol. H NMR (300 MHz, CDCl3) δ 0.81-1.86 (66H), 2.02 (s, 24H; -CH3), 2.38 (s, 12H; -CH3), 4.03(t, 12H; -OCH2), 5.83(d, 2H; -CH2), 6.77(d, 2H), 6.93(s, 4H ), 6.98-7.14 (6H), 7.30 (6H), 7.48 (6H), 8.03 (s, 2H). GPC: Mw/Mn = 29000/9000 = 3.2. Preparation of CMP1. To a stirred solution of (E),(E)-1,4-Bis(4-formyl-3,5-dimesitylstyryl)-2,5-di-n- hexyloxybenzene (101 mg, 0.100 mmol) and 5,5‟-bis(diethylphosphonylmethyl)-2,2‟- bipyridine (45.6 mg, 0.0950 mmol) in 25 mL THF was added dropwise a solution of KOtBu (37 mg, 0.330 mmol) in 20 mL THF at room temperature. After 24 h of stirring at room temperature, the solution was removed from the dry box and poured into 50 mL of 10% methanolic HCl and the resultant solid collected by filtration. The crude yellow solid was taken up in dichloromethane and the organic layer was washed with water and concentrated to a volume of about 2 mL. The concentrated solution was added to 77 methanol (6 mL) to precipitate a bright yellow solid that was subsequently dried, rinsed with pentane, and dried in vacuo to yield CMP1 (65 mg, 59%). GPC: Mw = 51,600, Mn = 1 24,600 g/mol, PDI = 2.1. H NMR (CDCl3, 300 MHz): δ 0.70-0.95 (m, 6H), 1.15-1.90 (m, 12H), 2.05 (s, 24H), 2.39 (s, 12H), 3.95-4.2 (m, 4H), 5.65-5.90 (m, 2H), 6.55-6.80 (m, 2H), 7.00 (s, 8H), 7.05-7.25 (m, 6H), 7.40-7.60 (m, 2H), 7.90-8.30 (m, 4H). Optical Response of CMP1 to Metal Ions. PL Response of CMP1 to excess Metal Ions. For each metal ion tested, a 3 mL aliquot of CMP1 (1 μM in THF) was placed in a cuvette and an initial PL spectrum collected. A 30 μL (20 equiv) aliquot of a 100 μM solution of the requisite metal salt was then added, and the cell was capped. After the cuvette was inverted several times to affect mixing, another PL spectrum was acquired. The excitation wavelength was 437 nm in all cases. Metal salts used for ion screening were K(PF6), Na(PF6), Mg(SO4), CaCl2, Eu(NO3)3, Zn(ClO4)2·6H2O, Cd(ClO4)2·6H2O, Cu(ClO4)2·6H2O, Hg(O2CCF3)2 and Ni(SO4). Absorption response of CMP1 to excess metal ions. For each metal ion tested, a 3 mL aliquot of CMP1 (10 μM in THF) was placed in a cuvette, and an initial UV-vis spectrum was collected. A 30 μL (20 equiv) aliquot of a 1 mM solution of the requisite metal salt was then added, and the cell was capped. After the cuvette was inverted several times to affect mixing, another PL spectrum was acquired. Fluorescence titration of CMP1 with metal ions. A 1 μM solution of CMP1 was prepared in anhydrous THF under an atmosphere of nitrogen. The solution was filtered, and a 3 mL aliquot of this solution was added to 78 the cell and an initial PL spectrum was acquired with an excitation wavelength of 437 nm. Small (3 μL) aliquots of a 100 μM solution of metal ion salts in THF were added, where each 3 μL aliquot represents 0.10 equiv of metal ion with respect to CMP1. A total of 60 μL of the solution was added, and progressive change in fluorescence with added metal ion was monitored. 79 REFERENCES CITED 1. Heeger, A. J., Angewandte Chemie, International Edition 2001, 40 2591-2611. 2. MacDiarmid, A. G., Angewandte Chemie, International Edition 2001, 40 2581- 2590. 3. Shirakawa, H., Angew. Chem., Int. Ed. 2001, 40 2575-2580. 4. Brabec, C. J.; Sariciftci, N. S.; Hummelen, J. C., Advanced Functional Materials 2001, 11 15-26. 5. Thompson, B. C.; Frechet, J. M. J., Angew. Chem., Int. Ed. 2008, 47 58-77. 6. Grimsdale, A. C.; Leok Chan, K.; Martin, R. E.; Jokisz, P. G.; Holmes, A. B., Chem. Rev. 2009, 109 897-1091. 7. Yamamoto, T.; Hayashida, N., Reactive & Functional Polymers 1998, 37 1-17. 8. Holliday, B. J.; Swager, T. M., Chem. Commun. 2005, 23-36. 9. Wolf, M. O., Advanced Materials 2001, 13 545-553. 10. Kohler, A.; Wilson, J., Organic Electronics 2003, 4 179-189. 11. Wohlgenannt, M.; Vardeny, Z. V., Journal of Physics: Condensed Matter 2003, 15 R83-R107. 12. Wilson, J. S.; Dhoot, A. S.; Seeley, A. J.; Khan, M. S.; Kohler, A.; Friend, R. H., Nature 2001, 413 828-31. 13. Kaes, C.; Katz, A.; Hosseini, M. W., Chemical Reviews 2000, 100 3553-3590. 14. Schubert, U. S.; Eschbaumer, C., Angewandte Chemie, International Edition 2002, 41 2892-2926. 80 15. Wang, B.; Wasielewski, M. R., Journal of the American Chemical Society 1997, 119 12-21. 16. Kern, J.-M.; Sauvage, J.-P.; Bidan, G.; Divisia-Blohorn, B., Journal of Polymer Science, Part A: Polymer Chemistry 2003, 41 3470-3477. 17. Divisia-Blohorn, B.; Genoud, F.; Borel, C.; Bidan, G.; Kern, J.-M.; Sauvage, J.- P., Journal of Physical Chemistry B 2003, 107 5126-5132. 18. Sauvage, J.-P.; Kern, J.-M.; Bidan, G.; Divisia-Blohorn, B.; Vidal, P.-l., New Journal of Chemistry 2002, 26 1287-1290. 19. Buey, J.; Swager, T. M., Angewandte Chemie, International Edition 2000, 39 608-612. 20. Vidal, P.-L.; Divisia-Blohorn, B.; Bidan, G.; Kern, J.-M.; Sauvage, J.-P.; Hazemann, J.-L., Inorganic Chemistry 1999, 38 4203-4210. 21. Vidal, P. L.; Divisia-Blohorn, B.; Billon, M.; Bidan, G.; Kern, J. M.; Sauvage, J. 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N.; Windscheif, P. M.; Evans, U.; Myrick, M. L.; Bunz, U. H. F., Macromolecules 2002, 35 8681-8683. 52. Odobel, F.; Massiot, D.; Harrison, B. S.; Schanze, K. S., Langmuir 2003, 19 30- 39. 53. Smith, R. C.; Gleason, L. B.; Protasiewicz, J. D., J. Mat. Chem. 2006, 16 2445- 2452. 54. Bao, Z.; Chen, Y.; Cai, R.; Yu, L., Macromolecules 1993, 26 5281-5286. 84 CHAPTER FOUR DIZINC ENZYME MODEL/COMPLEXOMETRIC INDICATOR PARIS IN INDICATOR DISPLACEMENT ASSAYS FOR INORGAINC PHOSPHATES UNDER PHYSIOLOGICAL CONDITIONS 4.1. Phosphate Ions in Biological System Inorganic phosphates (IPs) and organophosphorus species (OPs) play a number of key roles in physiology and pathophysiology. The fidelity of genetic replication relies on robust phosphoester linkages that make up DNA and RNA backbones. Even the simplest inorganic phosphorus oxyanion, phosphate, is involved in enumerable biological processes. Heightened phosphate levels (hyperphosphatemia) lead to renal failure, and phosphate deficiency (hypophosphatemia) is responsible for hyperthyroidism and rickets.180 Phosphate is also a biological buffer, notably intracellularly, in the urinary tract, and in saliva where it buffers against bacterial acid-induced tooth decay.181, 182 4- Pyrophosphate (P2O7 , often abbreviated PPi) is the product of ATP hydrolysis, the hallmark reaction of bioenergetics and metabolism, which regulates numerous enzymatic reactions.183 Phosphorylation is an important post-translational modification affecting protein structure and function through allosteric activation.184, 185 Phospholipids are also key cell membrane components. Many senescence theories and associated preventative medicines focus on phospholipid bilayer deterioration as a primary cause of aging.186-188 Pathophysiological responses can also result from xenobiotic OPs. Organophosphorus pesticides and the nerve agents of chemical warfare are among the most toxic substances 85 ever isolated.129, 189 These OPs induce toxic effects primarily by phosphorylation of a serine residue within the active site of acetylcholinesterase, leading to excess cholinergic stimulation within the synaptic cleft.190 Environmentally, phosphate is an essential soil nutrient for healthy plant growth and is a common component in agricultural supplementation.191-193 abs1 emit1 I A abs2 emit2 A I R R + Scheme 4.1. Generalized representation of the signal transduction mechanism for indicator displacement assays (IDAs). I = indicator, A = analyte, R = receptor. Emission or absorption intensity or wavelength maxima may change between bound and unbound states. The multifaceted role of inorganic phosphates and their phosphoester derivatives in biology and the environment has led researchers to develop various means of detecting these species. UV-vis and fluorescence-based optical methods have been particularly pursued due to the convenient visual („by eye‟) detection provided by colorimetric assays and the high sensitivity of fluorescence methods. The indicator displacement assay (IDA) strategy is a simple and increasingly-popular approach to optical detection. In this strategy (Scheme 4.1), a receptor is designed to bind a target analyte with a desired 86 affinity, and an indicator is selected having a weaker affinity for the receptor than does the target analyte. The indicator must also exhibit a notable optical change upon displacement, thereby providing a means of assessing analyte presence and quantifying concentration spectroscopically. The IDA strategy has emerged as an attractive alternative to covalently-tethered receptor-reporter constructs due to synthetic simplification and applicability of a single receptor to differentiation of various analytes.194, 195 Anslyn has pioneered IDAs for amino acids196, 197 and carboxylates present in beverages,198-203 for example. Other groups developing IDAs for similar analytes have focused on metal complexes as receptors.204-209 Fluorescent IDAs for detecting nitric oxide (NO)104-106, 210 exhibiting emission enhancement upon displacement of fluorogenic ligands from quenching transition metal centers have proven effective under physiological conditions, and have even been used to image NO synthesis by living cells.210 IDAs for phosphate derivatives, the analytes of interest in the current study, have also been explored.208, 211 Neutral organophosphorus nerve agent simulants can be detected via metal ion displacement from fluorogenic 2,6-bis(1‟- methylbenzimidazolyl)pyridine ligands,130 while IDAs for anionic phosphate derivatives212, 213 often utilize dizinc complexes as the receptor module. Dizinc phosphohydrolase model complexes supported by L1 (Chart 4.1) have proven to be 213-220 particularly useful receptors for IDAs. Chemosensors using the Zn2L1 receptor or a derivative thereof have demonstrated stability in vivo, as exemplified by a recent application to imaging bacterial infection in live mice.212 Complexometric indicators are 87 well-known for their dramatic color changes in response to metal ions and are widely used for metal ion detection. As such, they are also obvious candidates to Chart 4.1. Dinucleating ligand and complexometric dyes used in the current study. Only one protonation state and resonance structure is shown in each case. Ligand L1 is shown in the phenolate form present in the Zn2L1 complex. serve as displaceable chromophores from metal complex receptors in IDAs. Preliminary studies in this vein have used pyrocatechol violet (PV) or other indicator molecules 88 221 222-224 binding the Zn2L1 center via a catecholate moiety as the displaced indicator. Although the interaction of complexometric indicators with single metal ions in solution has been well-studied,99, 225-230 knowledge of analogous binding interactions between these indicators and bimetallic centers remains incomplete. The current work examines in detail the binding of eleven well-known, commercially-available complexometric indicators (Chart 4.1) 4.2 Results and Discussion The ligand L1 was selected for the current study because this ligand set and its derivatives have been utilized in indicator displacement and other sensing schemes under physiological conditions. L1 was prepared by the condensation of di(2-picolyl)amine and 2,6-bis(chloromethyl)-4-methylphenol in THF in the presence of triethylamine following the reported procedure,231 and its identity was confirmed by 1H and 13C NMR spectroscopy (Appendix A5-6). The Zn2L1 complex used in complexometric and displacement studies was prepared in situ by addition of 2 equiv ZnCl2 to L1 in 10 mM HEPES buffer at pH 7.4. Among the various metals that may bind the di(2-picolyl)amino (DPA) ligating group in L1, zinc is the logical choice for a physiological, reversibly binding receptor due to its air stability and the relatively high kinetic liability of its complexes. Furthermore, phenolate/DPA-supported complexes display high affinity (on the nanomolar range in some cases) for Zn2+ in living tissue.93, 97, 232 These features suggest that while the indicator may be displaced, Zn2L1 itself will not be readily demetallated in biological contexts and is thus a stable scaffold for biosensor applications. 89 A set of eleven commercially available complexometric indicators were selected for screening (Chart 4.1). Each indicator shown in Chart 4.1 was titrated with a solution of preformed Zn2L1 complex in HEPES (10 mM, pH 7.4), and absorption changes were monitored by UV-vis spectroscopy. Spectra for one titration (using ZC) are presented in Figure 4.1, while the complete set of titration spectra is provided in the Appendix B6-36. A modification of the classic Benesi-Hildebrand method87 was used to extract dissociation constants (Kd) from titration data for each indicator (Table 4.1; all plots and linear fits are provided in the Appendix D1-11). Among the indicators screened, Kd values cover two orders of magnitude, from 2.8×10-4 M to 2.7×10-6 M (Table 4.1). Significant variation due to steric and electronic influences is noted even for indicators that presumably bind to Zn2L1 through the same ligating unit. For example, indicators 221 binding through a catecholate (ARS, BPR, GC, and PV) have Kd values ranging from 2.8×10-4 M to 2.7×10-6 M, and the values for Eriochrome dyes ERB and EBBB, both of which are expected to bind metals via a phenolate and an azo nitrogen,233-235 are 4.0 ×10-5 M and 8.2×10-6 M, respectively. MX, which can bind a single metal ion in a tridentate N– 236 -5 O–N fashion, binds within the same range (Kd = 2.1×10 M). Among the indicators examined, the only Kd previously reported was for the PV-Zn2L1 complex. The reported value of 1.9×10-5 M,223 determined from calorimetric and UV-vis data in HEPES at pH 7.0 (also reported in TES buffer at pH 7.4),222 is in good agreement with that determined in the current study (3.0×10-5 M). The variation of binding constant with small pH/buffer 90 a Indicator Kd free bound Displacement 2- 2- M nm nm nm HPO4 H2P2O7 ARS 280 516 541 25 Y Y BPR 2.7 554 578 24 N Y DT 13 471 487 16 N Yb EBBB 8.2 649 454 195 Y Y ERB 40 469 510 41 Y Y GC 18 621 563 58 Y Y MB9 5.1 532 544 12 N Y MX 21 520 480 40 Y Y PAR 18 412 490 78 Y Y PV 30 443 635 192 Y Y ZC 2.9 467 563 96 Y Y a) Displacement is considered to take place when there is a >50% return in absorbance at bound to the absorbance at that wavelength for the unbound form. b) Displacement requires ~1 min before it can be observed, whereas all other positive displacement events are observed immediately upon mixing. 91 Table 4.1. Absorption data and photos demonstrating the range of colorimetric responses observed in free, bound and pyrophosphate-displaced states. Absorption spectra for these experiments are provided in the Appendix B17-36. changes is the likely origin of the difference between the two values. BPR and ZC bind to Zn2L1 most strongly and approximately an order of magnitude more strongly than does PV, compared with the weakest binding, observed for ARS, an order of magnitude less strongly binding than PV. The availability of a wide range of Kd values is invaluable for the design of IDAs with specified responses (vide infra). Another parameter of interest in the design of colorimetric IDAs is the extent to which the color changes upon exposure to analyte. Photographs are provided in Table 4.1 for bound and free forms of the indicators, demonstrating the range of wavelengths available within the indicator series. EBBB exhibits the greatest change in max between free and Zn2L1-bound states ( = 195 nm, Table 4.1), making it very easy to follow binding and displacement events by eye. The smallest shift is observed for MB9, with max of only 12 nm between bound and unbound states. This change is still visible to the naked eye in a side-by-side comparison, but is considerably less pronounced than that for some of the other dyes. Once the binding of indicators to Zn2L1 had been quantitated, phosphate and pyrophosphate were selected as test analytes to gauge their ability to displace indicators with restoration of the “unbound” color. These analytes were selected to allow comparison of the series of indicators screened in this study with previous IDAs for these analytes utilizing the Zn2L1 receptor. Furthermore, previous studies have already 92 +Zn L1 (A) 2 +Zn2L1 +Zn2L1 (B) (C) Figure 4.1. (A) Titration of ZC with Zn2L1, followed by UV-vis spectroscopy (the solvent is 10 mM HEPES at pH 7.4). (B) Phosphate displacement test; the red trace corresponds to ZC, the blue trace to the ZC-Zn2L1 complex, and the purple trace ZC- 2– Zn2L1 complex in the presence of HPO4 . (C) Pyrophosphate displacement test; the red 93 trace corresponds to ZC, the blue trace to the ZC-Zn2L1 complex, and the purple trace 2– ZC-Zn2L1 complex in the presence of H2P2O7 . demonstrated little or no binding affinity of other common anions such as nitrate, sulfate, acetate, or halides to this receptor.49 Crystallographically characterized compounds of phosphate and pyrophosphate anions with bimetallic complexes closely related to Zn2L1 indicate their probable binding modes.237 Phosphate bridges the two metal centers in a - 2-O,O’ fashion.238 Pyrophosphate binds within the bimetallic cleft of a dizinc complex similar to Zn2L1 wherein which two oxygens on each P atom coordinate one zinc ion in a 2 237 -6 -O,O’ fashion Pyrophosphate (Kd = 1.5×10 M) is bound about six times more -6 239 strongly than phosphate (Kd = 9.1×10 M) in 1:1 complexes with Zn2L1. On the basis of equilibrium considerations, displacement of >50% of indicator by 1 equiv of analyte will occur when Kd, indicator > Kd, analyte. Assuming that indicator binding is reversible and that there is no significant kinetic barrier to displacement, a colorimetric response corresponding to at least partial restoration of the indicator to its uncomplexed form would be expected in such cases. An indicator that binds to Zn2L1 with a Kd significantly higher than both analytes should be easily displaced by either of them, so selectivity cannot be accomplished in these cases. This prediction holds true for six of the seven indicators in this category (ARS, ERB, GC, MX, PAR, and PV), all of which immediate return to the color of the unbound indicator upon addition of phosphate or pyrophosphate. The exception is DT, which requires ~1 min for displacement following anion addition. 94 49 Although an IDA for phosphate employing PV-Zn2L1 was previously noted, pyrophosphate was not tested as a competing analyte, and this IDA cannot distinguish between the two anions at physiological pH. In order to accomplish selective detection of the more strongly binding pyrophosphate from an equal concentrations of phosphate, the indicator selected must bind to Zn2L1 with Kd between the values for phosphate and pyrophosphate (between 1.5 and 9.1 μM). The narrow range afforded by these analytes makes selective detection a challenge. In the current series, BPR, MB9 and ZC have 208 appropriate Kd values expected to facilitate such a selective response. The binding constant for EBBB is in this range as well but is nearly identical to that of phosphate, and we were not able to observe selectivity in this case. A selective response to 1 equiv pyrophosphate over equimolar phosphate is evident, both visually and spectroscopically, when BPR, MB9, or ZC is used as the indicator. The selectivity of the ZC-based IDA for pyrophosphate (Figure 4.1c) over phosphate (Figure 4.1b) is evident from the absorption spectra as well as by eye. The violet ZC-Zn2L1 complex changes to the orange color typical of free ZC immediately upon addition of pyrophosphate, but changes little in upon addition of phosphate. The phosphate/pyrophosphate displacement described herein is another illustrative example of the IDA strategy‟s simplicity; a single receptor can be utilized with a range of indicators to give different responses and selectivities that depend on the relative binding affinities of the analyte and indicator selected. The dissociation constants determined in the current study for this set of commercially available indicators should guide their application in future IDAs. 95 4.4 Conclusions A series of eleven complexometric indicators was investigated for spectral response to a dizinc phosphohydrolase model complex Zn2L1. Dissociation constants determined for eleven of these complexes span two orders of magnitude. These eleven indicators were tested for displacement by phosphate and pyrophosphate anions in HEPES buffer at physiological pH of 7.4. Selective indicator displacement assays for pyrophosphate were discovered using BPR, MB9, or ZC as displaceable indicators. Differentiation of analytes relies heavily on the relative binding constants of the indicator and analyte(s) of interest. The binding data presented herein will guide our future application of biologically-applicable sensors utilizing this set of dyes. Work to expand upon these data and to prepare more selective dizinc receptors for anion detection by indicator displacement are currently underway in our laboratory. Experimental General Consideration Procedures for Absorption Spectroscopy. Absorption spectra were collected using a Varian Cary-50 Bio spectrophotometer in poly(methylmethacrylate) cuvettes with a path length of 1 cm. Titrations of indicators, monitored by UV-vis spectroscopy (Appendix B6-16) were carried out by progressively -5 adding aliquots of Zn2L1 (0.1 equiv at a time) to ~5×10 M solutions of the indicator in HEPES (10 mM, pH 7.4). The titration was monitored up to 2 equiv Zn2L1 were added in -5 each case. Displacement of indicators from a 1:1 indicator:Zn2L1 solution (also ~5×10 96 M) involved addition of 1 equiv phosphate, and up to 10 equiv of anion was added in some cases to confirm low responsiveness. Materials. Ligand L1 was prepared as reported previously70 and its identity confirmed by 1H and 13C NMR spectra (Appendix A5-6) obtained using a Bruker Advance 300 operating at 300 MHz for proton and 75 MHz for carbon-13 at 25 °C. Peaks are reported in ppm with reference to TMS or residual CDCl3 solvent signal. Other reagents and indicators were used as received from the suppliers without further purification. Buffer pH was measured using a Corning CHEK-MITE pH 25 sensor equipped with a symphony Ag/AgCl pH electrode, and adjusted to the target value by addition of HCl(aq) and NaOH(aq) solutions. Binding constants were determined using variations of the Benesi- Hildebrand method recommended by Hammond.71 97 CHAPTER FIVE CONCLUSIONS AND FUTURE DIRECTIONS 1.1 Metallofluoropolymers The preparation of FAVEs via metal-free protocol that serves as an effective macromolecular metal ligating scaffold has proven its strong ionochromic response to metal ions. A highly selective 10-fold turn-on fluorescence response to Zn2+ ions was obtained. The Zn2+-P1 metallopolymer would be an effective ratiometric fluorescent indicator for fluoride, while the Cu2+-P1 metallopolymer affords a highly-responsive turn-on fluorescence response to fluoride or cyanide. Extension studies of FAVE could be the synthetic route used herein to prepare additional metal-chelating FAVEs, as well as application of P1 derivatives in thin film and handheld decvices for detections of nerve agents. 1.2. Bulky polymers In the study of applying TAB as the steric control approachs along the polymer backbone has demonstrated its ability to enable 1:1 binding ratio of bipy unit and metal ions. The presents of TAB in poly(p-phenylene ethynylene), polyfluorene and poly(p-phenylene vinylene) derivatives has shown solid effects in solubity enhancement and aggregations suppression. 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D., Tetrahedron Letters 2004, 45 8721-8724. 119 120 121 122 123 124 125 126 127 128 129 Appendix A NMR spectra 130 HO N N OH Figure A-1. Proton NMR spectrum (300 MHz, DMSO) of 5,5‟-Bis(4-hydroxystyryl)- 2,2‟-bipyridine (the structure is shown as an inset). 131 HO N N OH Figure A-2. Carbon-13 NMR spectrum (75.6 MHz, DMSO) of 5,5‟-Bis(4- hydroxystyryl)-2,2‟-bipyridine (the structure is shown as an inset). 132 Figure A-3. Proton NMR spectrum (300 MHz, DMSO) of P1. 133 Figure A-4. Fluorine-19 NMR spectrum (283 MHz, DMSO) of P1. 134 Figure A-5. Proton NMR spectrum of H-L1 (CDCl3, 300 MHz). Peak marked with an asterisk is due to residual solvent signal. Some residual diethyl ether from recrystallization is also present. 135 Figure A-6. Carbon-13 NMR spectrum of H-L1 (CDCl3, 75 MHz). The peak labeled with an asterisk is due to CDCl3. 136 Figure A-7. Proton NMR spectra of 2-(4-bromo-2,6-dimesitylphenyl)-1,3-dioxolane in CDCl3 (300 MHz). 137 Figure A-8. Carbon-13 NMR spectra of 2-(4-bromo-2,6-dimesitylphenyl)-1,3-dioxolane in CDCl3 (300 MHz). 138 Figure A-9. Proton NMR spectra of 4-iodo-2,6-dimesitylbenzaldehyde in CDCl3(300 MHz). 139 Figure A-10. Carbon-13 NMR spectra of 4-iodo-2,6-dimesitylbenzaldehyde in CDCl3(300 MHz). 140 Figure A-11. Proton NMR spectra of 5‟-bis(4-iodo-2,6-dimesitylstyryl)-2,2‟-bipyridine in CDCl3 (300 MHz). 141 Figure A-12. Carbon-13 NMR spectra of 5‟-bis(4-iodo-2,6-dimesitylstyryl)-2,2‟- bipyridine in CDCl3 (300 MHz). 142 Figure A-13. Proton NMR spectra of 5‟-bis(4-bromo-2,6-dimesitylstyryl)-2,2‟-bipyridine in CDCl3 (300 MHz). 143 Figure A-14. Carbon-13 NMR spectra of 5‟-bis(4-bromo-2,6-dimesitylstyryl)-2,2‟- bipyridine in CDCl3 (300 MHz). 144 [PdCl2(Br-TAB-Br)] Figure A-15. Proton NMR spectra of [PdCl2(Br-TAB-Br)] in THF-d8 (300 MHz). 145 [PdCl2(Br-TAB-Br)] Figure A-16. Proton NMR spectra of [PdCl2(Br-TAB-Br)] in THF-d8 (300 MHz). 146 Figure A-17. Proton NMR spectrum of 1,4-bis(hexyloxyl)-2,5-diiodobenzene in CDCl3 (300 MHz). 147 Figure A-18. Proton NMR spectrum of 2,7-diiodo-9,9-dioctyl-9H-fluorene in CDCl3 (300 MHz). 148 Figure A-19. Proton NMR spectrum of PF1 in CDCl3 (300 MHz). 149 Figure A-20. Proton NMR spectrum of PF3 in CDCl3 (300 MHz). 150 Figure A-21. Proton NMR spectrum of PPE1 in CDCl3 (300 MHz). 151 Figure A-22. Proton NMR spectrum of PPE3 in CDCl3 (300 MHz). 152 Appendix B UV-vis and Photoluminescence Spectra 153 350 0.3 uM DWS 157 300 10 equiv K 10 equiv Na 10 equiv Ca 250 10 equiv Mg 10 equiv Eu 200 10 equiv Hg 10 equiv Cd Relative IntensityRelative 150 10 equiv Ni 10 equiv Co 10 equiv Cu(II) 100 10 equiv Zn 10 equiv Fe(II) 50 10 equiv Cu(I) 0 380 430 480 530 580 630 Wavelength (nm) Figure B-1. Fluorescence Response of P1 (0.3 μM in THF) to 10 equiv of various metals (λex = 370 nm). 154 500 6 uM DWS157 0.01 equiv Co 400 0.02 equiv Co +Co(II) 0.03 equiv Co 300 0.04 equiv Co 0.05 equiv Co 0.06 equiv Co 200 Relative IntensityRelative 0.07 equiv Co 0.08 equiv Co 100 0.09 equiv Co 0.1 equiv Co 0 380 430 480 530 580 630 Wavelength (nm) Figure B-2. Titration of P1 (6 μM in THF) with Co(II) (λex = 370 nm). 155 6 uM DWS 900 157 0.01 equiv Cu 800 0.02 equiv Cu 700 +Cu(II) 0.03 equiv Cu 600 0.04 equiv Cu 500 0.05 equiv Cu 0.06 equiv Cu 400 Relative IntensityRelative 0.07 equiv Cu 300 0.08 equiv Cu 200 0.09 equiv cu 100 0.1 equiv Cu 0 380 480 580 Wavelength (nm) Figure B-3. Titration of P1 (6 μM in THF) with Cu(II) (λex = 370 nm). 156 160 6 uM DWS 157 0.002 equiv Hg 140 0.004 equiv Hg 120 0.006 equiv Hg 100 +Cd(II) 0.008 equiv Hg 0.01 equiv Hg 80 0.012 equiv Hg Relative IntensityRelative 60 0.014 equiv Hg 40 0.016 equiv Hg 0.018 equiv Hg 20 0.020 equiv Hg 0 430 480 530 580 630 Wavelength (nm) Figure B-4. Fluorescence Response of P1 to Cd(II) (λex = 420 nm). 157 160 6 uM DWS 157 0.002 equiv Hg 140 0.004 equiv Hg 120 0.006 equiv Hg 100 +Hg(II) 0.008 equiv Hg 0.01 equiv Hg 80 0.012 equiv Hg Relative IntensityRelative 60 0.014 equiv Hg 40 0.016 equiv Hg 0.018 equiv Hg 20 0.020 equiv Hg 0 430 480 530 580 630 Wavelength (nm) Figure B-5. Fluorescence Response of P1 to Hg (II) (λex = 420 nm). 158 ARS Structure: +Zn2L1 +Zn2L1 +Zn2L1 +Zn2L1 Figure B-6. Titration of Alizarin Red S (ARS). 159 BPR Structure: +Zn2L1 +Zn2L1 Figure B-7. Titration of Bromo Pyrogallol Red (BPR). 160 DT Structure: +Zn2L1 Figure B-8. Titration of Dithizone (DT). 161 EBBB Structure: +Zn L1 2 Figure B-9. Titration of Eriochrome Blue Black B (EBBB). 162 ERB Structure: +Zn2L1 +Zn2L1 +Zn2L1 Figure B-10. Titration of Eriochrome Red B (ERB). 163 GC Structure: +Zn L1 2 Figure B-11. Titration of Gallocyanine (GC). 164 MB9 Structure: +Zn L1 2 +Zn2L1 Figure B-12. Titration of Mordant Blue 9 (MB9) 165 MX Structure: +Zn2L1 +Zn2L1 Figure B-13. Titration of Murexide (MX). 166 PAR Structure: +Zn2L1 +Zn2L1 +Zn2L1 Figure B-14. Titration of 4-(Pyridin-2-ylazo)resorcinol (PAR). 167 PV Structure: +Zn2L1 +Zn2L1 +Zn L1 2 Figure B-15. Titration of Pyrocatechol Violet (PV). 168 ZC Structure: +Zn2L1 +Zn2L1 +Zn2L1 Figure B-16. Titration of Zincon (ZC). 169 ARS Structure: Figure B-17. Phosphate displacement tests for Alizarin Red S (ARS). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 170 ARS Structure: Figure B-18. Pyrophosphate displacement tests for Alizarin Red S (ARS). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 171 EPR Structure: Figure B-19. Phosphate displacement tests for Bromo Pyrogallol Red (BPR). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)- Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion.. 172 EPR Structure: Figure B-20. Pyrophosphate displacement tests for Bromo Pyrogallol Red (BPR). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)- Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 173 DT Structure: Figure B-21. Phosphate displacement tests for Dithizone (DT). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. Approximately 1 min is required for displacement to reach equilibrium. 174 DT Structure: Figure B-22. Pyrophosphate displacement tests for Dithizone (DT). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. Approximately 1 min is required for displacement to reach equilibrium. 175 EBBB Structure: Figure B-23. Phosphate displacement tests for Eriochrome Blue Black B (EBBB). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)- Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 176 EBBB Structure: Figure B-24. Pyrophosphate displacement tests for Eriochrome Blue Black B (EBBB). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 177 complex plus the anion. ERB Structure: Figure B-25. Phosphate displacement tests for Eriochrome Red B (ERB). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 178 179 ERB Structure: Figure B-26. Pyrophosphate displacement tests for Eriochrome Red B (ERB). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)- Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 180 GC Structure: Figure B-27. Phosphate displacement tests for Gallocyanine (GC). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 181 GC Structure: Figure B-28. Pyrophosphate displacement tests for Gallocyanine (GC). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 182 MB9 Structure: Figure B-29. Phosphate displacement tests for Mordant Blue 9 (MB9). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 183 MB9 Structure: Figure B-30. Pyrophosphate displacement tests for Mordant Blue 9 (MB9). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 184 MX Structure: Figure B-31. Phosphate displacement tests for Murexide (MX). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 185 MX Structure: Figure B-32. Pyrophosphate displacement tests for Murexide (MX). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 186 PAR Structure: Figure B-33. Phosphate displacement tests for 4-(Pyridin-2-ylazo)resorcinol (PAR). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)- Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 187 PAR Structure: Figure B-34. Pyrophosphate displacement tests for 4-(Pyridin-2-ylazo)resorcinol (PAR). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 188 ZC Structure: Figure B-35. Phosphate displacement tests for Zincon (ZC). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 189 ZC Structure: Figure B-36. Pyrophosphate displacement tests for Zincon (ZC). The red trace corresponds to the indicator alone, the blue trace corresponds to the (indicator)-Zn2L1 complex, and the purple trace corresponds to (indicator)-Zn2L1 complex plus the anion. 190 0.4 0.35 0.3 0.25 0.2 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) K Na Ca Mg Hg Co Cd Zn Cu Figure B-37. Absorption spectrum for PF1 (initial concentration of 5.7 × 10-7 M) in the presence of 10 equiv. of the indicated metal ions in THF. 191 700 600 500 400 300 Intensity 200 100 0 400 450 500 550 600 Wavelength (nm) +Eu +K +Na +Mg +Ca +Hg +Zn +Cu +Co +Cd Figure B-38. Photoluminescence spectrum for PF1 (initial concentration of 2.0 × 10-7 M) in the presence of 10 equiv. of the indicated metal ions in THF. 192 +Cd(II) 0.25 0.2 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-39. Absorption titration spectrum for PF1 (initial concentration of 5.7 × 10-7 M) to Cd(ClO4)2 in THF. 193 700 600 +Cd(II) 500 400 300 Intensity 200 100 0 400 450 500 550 600 Wavelength (nm) Figure B-40. Photoluminescence titration spectrum for PF1 (initial concentration of 2.0 -7 × 10 M) to Cd(ClO4)2 in THF. 194 0.06 +Cu(II) 0.05 0.04 0.03 0.02 Absorbance 0.01 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-41. Absorption titration spectrum for PF1 (initial concentration of 5.7 × 10-7 M) to Cu(ClO4)2 in THF. 195 1,000 +Cu(II) 800 600 400 Intensity 200 0 400 450 500 550 600 Wavelength (nm) Figure B-42. Photoluminescence titration spectrum for PF1 (initial concentration of 2.0 -7 × 10 M) to Cu(ClO4)2 in THF. 196 0.25 +Hg(II) 0.2 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-43. Absorption titration spectrum for PF1 (initial concentration of 5.7 × 10-7M) to Hg(O2CCF3)2 in THF. 197 800 700 +Hg(II) 600 500 400 Intensity 300 200 100 0 400 450 500 550 600 Wavelength (nm) Figure B-44. Photoluminescence titration spectrum for PF1 (initial concentration of 2.0 -7 × 10 M M) to Hg(O2CCF3)2 in THF. 198 0.25 +Co(II) 0.2 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-45. Absorption titration spectrum for PF1 (initial concentration of 5.7 × 10-7 M) to Co(NO3)2 in THF. 199 700 600 +Co(II) 500 400 300 Intensity 200 100 0 400 450 500 550 600 Wavelength (nm) Figure B-46. Photoluminescence titration spectrum for PF1 (initial concentration of 2.0 -7 × 10 M) to Co(NO3)2 in THF. 200 0.25 +Zn(II) 0.2 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-47. Absorption titration spectrum for PF1 (initial concentration of 5.7 × 10-5 M) to Zn(ClO4)2 in THF. 201 800 700 +Zn(II) 600 500 400 Intensity 300 200 100 0 400 450 500 550 600 Wavelength (nm) Figure B-48. Photoluminescence titration spectrum for PF1 (initial concentration of 2.0 -7 × 10 M) to Zn(ClO4)2 in THF. 202 0.3 0.25 0.2 0.15 0.1 Absorbance 0.05 0 300 400 500 600 Wavelength (nm) Co Cd Hg Zn Cu Na Ca K Eu Mg Figure B-49. Absorption spectrum for PF3 (initial concentration of 3.3 × 10-6 M) and in the presence of 20 equiv. of the indicated metal ions in THF. 203 600 450 300 Intensity 150 0 400 450 500 550 600 650 700 Wavelength (nm) Cu Zn Hg Co Cd K Mg Ca Na Figure B-50. Photoluminescence spectrum for PF3 (initial concentration of 3.3 × 10-6 M) and in the presence of 20 equiv. of the indicated metal ions in THF. 204 0.3 0.25 +Cd(II) 0.2 0.15 Absorbance 0.1 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-51. Absorption titration spectrum for PF3 (initial concentration of 3.3 × 10-6 M) to Cd(ClO4)2 in THF. 205 800 +Cd(II) 600 400 Intensity 200 0 400 450 500 550 600 650 700 Wavelength (nm) Figure B-52. Photoluminescence titration spectrum for PF3 (initial concentration of 3.3 -6 × 10 M) to Cd(ClO4)2 in THF 206 0.3 0.25 0.2 +Cu(II) 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-53. Absorption titration spectrum for PF3 (initial concentration of 3.3 × 10-6 M) to Cu(ClO4)2 in THF. 207 200 +Cu(II) 150 100 Intensity 50 0 400 450 500 550 600 650 700 Wavelength (nm) Figure B-54. Photoluminescence titration spectrum for PF3 (initial concentration of 3.3 -6 × 10 M) to Cu(ClO4)2 in THF. 208 0.30 0.25 +Hg(II) 0.20 0.15 0.10 Absorbance 0.05 0.00 300 370 440 510 580 Wavelength (nm) Figure B-55. Absorption titration spectrum for PF3 (initial concentration of 3.3 × 10-6 M) to Hg(O2CCF3)2 in THF. 209 +Hg(II) 600 450 300 Intensity 150 0 400 450 500 550 600 Wavelength (nm) Figure B-56. Photoluminescence titration spectrum for PF3 (initial concentration of 3.3 -6 × 10 M) to Hg(O2CCF3)2 in THF. 210 0.3 0.25 0.2 +Co(II) 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-57. Absorption titration spectrum for PF3 (initial concentration of 3.3 × 10-6 M) to Co(NO3)2 in THF. 211 +Co(II) 600 450 300 Intensity 150 0 400 450 500 550 600 650 700 Wavelength (nm) Figure B-58. Photoluminescence titration spectrum for PF3 (initial concentration of 3.3 -6 × 10 M) to Co(NO3)2 in THF. 212 0.3 0.25 +Zn(II) 0.2 0.15 Absorbance 0.1 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-59. Absorption titration spectrum for PF3 (initial concentration of 3.3 × 10-6 M) to Zn(ClO4)2 in THF. 213 700 600 +Zn(II) 500 400 300 Intensity 200 100 0 400 450 500 550 600 Wavelength (nm) Figure B-60. Photoluminescence titration spectrum for PF3 (initial concentration of 3.3 -6 × 10 M) to Zn(ClO4)2 in THF. 214 0.4 0.3 0.2 Absorbance 0.1 0 285 385 485 585 Wavelengths (nm) +Ca +Mg +Na +K +Cd +Co +Cu +Eu +Hg +Zn Figure B-61. Absorption spectrum for PPE1 (initial concentration of 2.2 × 10-5 M) and in the presence of 10 equiv. of the indicated metal ions in THF 215 250 200 150 Intensity 100 50 0 400 450 500 550 600 650 700 Wavelength (nm) +Ca +Mg +Na +K +Cu +Co +Zn +Hg +Cd +Eu Figure B-62. Photoluminescence spectrum for PPE1 (initial concentration of 2.2 × 10-6 M) and in the presence of 10 equiv. of the indicated metal ions in THF 216 0.3 0.25 +Cd(II) 0.2 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-63. Absorption spectrum for PPE1 (initial concentration of 2.2 × 10-5 M) to Cd(ClO4)2 in THF. 217 250 +Cd(II) 200 150 100 Intensity 50 0 400 450 500 550 600 Wavelength (nm) Figure B-64. Photoluminescence spectrum for PPE1 (initial concentration of 2.2 × 10-6 M) to Cd(ClO4)2 in THF 218 0.35 +Cu(II) 0.3 0.25 0.2 0.15 Absorbance 0.1 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-65. Absorption spectrum for PPE1 (initial concentration of 2.2 × 10-5 M) to Cu(ClO4)2 in THF. 219 250 +Cu(II) 200 150 100 Intensity 50 0 400 450 500 550 600 Wavelength (nm) Figure B-66. Photoluminescence spectrum for PPE1 (initial concentration of 2.2 × 10-6 M) to Cu(ClO4)2 in THF. 220 0.3 +Hg(II) 0.25 0.2 0.15 Absorbance 0.1 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-67. Absorption spectrum for PPE1 (initial concentration of 2.2 × 10-5 M) to Hg(O2CCF3)2 in THF. 221 250 +Hg(II) 200 150 100 Intensity 50 0 400 450 500 550 600 Wavelength (nm) Figure B-68. Photoluminescence spectrum for PPE1 (initial concentration of 2.2 × 10-6 M) to Hg(O2CCF3)2 in THF. 222 0.35 +Co(II) 0.3 0.25 0.2 0.15 Absorbance 0.1 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-69. Absorption spectrum for PPE1 (initial concentration of 2.2 × 10-5 M) to Co(NO3)2 in THF. 223 250 +Co(II) 200 150 100 Intensity 50 0 400 450 500 550 600 Wavelength (nm) Figure B-70. Photoluminescence spectrum for PPE1 (initial concentration of 2.2 × 10-6 M) to Co(NO3)2 in THF. 224 0.3 +Zn(II) 0.25 0.2 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-71. Absorption spectrum for PPE1 (initial concentration of 2.2 × 10-5 M) to Zn(ClO4)2 in THF. 225 250 +Zn(II) 200 150 100 Intensity 50 0 400 450 500 550 600 Wavelength (nm) Figure B-72. Photoluminescence spectrum for PPE1 (initial concentration of 2.2 × 10-6 M) to Zn(ClO4)2 in THF. 226 0.2 0.15 0.1 Intensity 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) K Cu Co Hg Cd Eu Zn Ca Mg Na Figure B-73. Absorption spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) and in the presence of excess (>20 equiv.) of the indicated metal ions in THF 227 400 300 200 Intensity 100 0 400 450 500 550 600 650 700 Wavelength (nm) Cu Cd K Co Hg Ca Eu Mg Zn Figure B-74. Photoluminescence spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) and in the presence of excess (>20 equiv.) of the indicated metal ions in THF 228 0.2 +Cd(II) 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-75. Absorption spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Cd(ClO4)2 in THF. 229 450 400 350 +Cd(II) 300 250 200 Intensity 150 100 50 0 400 450 500 550 600 Wavelength (nm) Figure B-76. Photoluminescence spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Cd(ClO4)2 in THF 230 0.2 +Cu(II) 0.15 0.1 0.05 Absorbance 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-77. Absorption spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Cu(ClO4)2 in THF. 231 350 +Cu(II) 300 250 200 150 Intensity 100 50 0 400 450 500 550 600 Wavelength (nm) Figure B-78. Photoluminescence spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Cu(ClO4)2 in THF. 232 0.2 +Hg(II) 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-79. Absorption spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Hg(O2CCF3)2 in THF. 233 400 +Hg(II) 300 200 Intensity 100 0 400 450 500 550 600 Wavelength (nm) Figure B-80. Photoluminescence spectrum for PPE3 (initial concentration of 1.2 × 10-6 M)to Hg(O2CCF3)2 in THF. 234 0.2 +Co(II) 0.15 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-81. Absorption spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Co(NO3)2 in THF. 235 350 300 +Co(II) 250 200 150 Intensity 100 50 0 400 450 500 550 600 Wavelength (nm) Figure B-82. Photoluminescence spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Co(NO3)2 in THF. 236 0.2 0.15 +Zn(II) 0.1 Absorbance 0.05 0 300 350 400 450 500 550 600 Wavelength (nm) Figure B-83. Absorption spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Zn(ClO4)2 in THF. 237 400 +Zn(II) 300 200 Intensity 100 0 400 450 500 550 600 Wavelength (nm) Figure B-84. Photoluminescence spectrum for PPE3 (initial concentration of 1.2 × 10-6 M) to Zn(ClO4)2 in THF. 238 Appendix C Single crystal X-ray diffraction structure 239 Figure C-1a. ORTEP drawing from the single crystal X-ray diffraction structure of 2-(4- bromo-2,6-dimesitylphenyl)-1,3-dioxolane (50% probability ellipsoids). Hydrogen atoms are omitted for clarity. 240 Empirical formula C27H29BrO2 Formula weight (g/mol) 465.41 Temperature (K) 163 (2) Wavelength (Å) 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a (Å) 8.134(1) b (Å) 9.735(2) c (Å) 14.893(2) α (deg) 89.772(6) β (deg) 87.329(6) γ (deg) 89.842(6) Volume (Å3) 1178.0(3) Z 2 Calculated density (Mg/m3) 1.312 Absorption coefficient (mm-1) 1.765 F(000) 484 Crystal size (mm) 0.43 × 0.29 × 0.22 Crystal color and shape colourless chip Θ range for data collection (deg) 3.26 - 25.10 Limiting indices -9 < h < 9 -11 < k < 11 -16 < l < 17 Reflections collected 9038 Independent reflections 4179 Completeness to Θ 25.10 (99.5 %) Max. transmission 0.6975 Min. transmission 0.5175 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4179/0/277 Goodness of fit on F2 1.081 Final R indices (I > 2σ(I)) R1 0.0411 wR2 0.0977 R indices (all data) R1 0.0549 wR2 0.1097 Figure C-1b. Refinement details for 2-(4-bromo-2,6-dimesitylphenyl)-1,3-dioxolane. 241 Figure C-2a. ORTEP drawing from the single crystal X-ray diffraction structure of [PdCl2(BrTABBr)] (30% probability ellipsoids). Hydrogen atoms are omitted for clarity. 242 Table C-2b. Refinement details for [PdCl2(Br-TAB-Br)]. Empirical formula C62H58Br2Cl2N2Pd Formula weight (g/mol) 1168.22 Temperature (K) 153 (2) Wavelength (Å) 0.71073 Crystal system Monoclinic Space group C2/c Unit cell dimensions a (Å) 48.072(10) b (Å) 8.9440(18) c (Å) 32.086(6) α (deg) 90.00 β (deg) 113.00(3) γ (deg) 90.00 Volume (Å3) 12699(4) Z 8 Calculated density (Mg/m3) 1.222 Absorption coefficient (mm-1) 1.670 F(000) 4752 Crystal size (mm) 0.43 × 0.24 × 0.06 Crystal color and shape yellow chip Θ range for data collection (deg) 2.76 – 25.10 Limiting indices -57 < h < 52 0 < k < 10 0 < l < 38 Reflections collected 23355 Independent reflections 11132 Completeness to Θ 25.10 (98.3 %) Max. transmission 0.9065 Min. transmission 0.5337 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 11132/0/634 Goodness of fit on F2 1.062 Final R indices (I > 2σ(I)) R1 0.0706 wR2 0.1937 R indices (all data) R1 0.0959 wR2 0.2138 243 Appendix D Benesi-Hildebrand plot of spectra 244 ARS Structure: y = 1.99E-04x + 7.13E-01 Alizarin Red S R2 = 0.99 Alizarin Red S 50 40 30 1/Abs 20 10 0 0 50000 100000 150000 200000 250000 1/[Zn2L1] Figure D-1. Titration of Alizarin Red S (ARS). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 245 BPR Structure: Bromo Pyrogallol Red y = 1.6936x + 4.5304 R2 = 1.0 100 75 50 [Zn2L1]/Abs 25 0 0 10 20 30 40 50 6 10 *[Zn2L1] Figure D-2. Titration of Bromo Pyrogallol Red (BPR). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 246 DT Structure: Dithizone y = 9.67E-01x + 2.62E+01 R2 = 0.98 200 160 120 [Zn2L1]/Abs 80 40 0 0 50 100 150 200 6 10 *[Zn2L1] Figure D-3. Titration of Dithizone (DT). Benesi-Hildebrand plot of spectral data points 2 (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 247 EBBB Structure: Eriochrome Blue Black B y = 1.93E+00x + 2.20E+01 R2 = 1.0 1200 900 [Zn2L1]/Abs 600 300 0 0 100 200 300 400 500 600 6 10 *[Zn2L1] Figure D-4. Titration of Eriochrome Blue Black B (EBBB). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 248 ERB Structure: Eriochrome Red B y = 3E-05x + 0.8575 R2 = 0.98 10 8 6 [Zn2L1]/Abs 4 2 0 10000 60000 110000 160000 210000 1/[Zn2L1] Figure D-5. Titration of Eriochrome Red B (ERB). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 249 GC Structure: Gallocyanine y = 1.18E+05x + 2.11E+00 R2 = 0.98 3.5 3 [Zn2L1]/Abs 2.5 2 0 0.000002 0.000004 0.000006 0.000008 0.00001 0.000012 [Zn2L1] Figure D-6. Titration of Gallocyanine (GC). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 250 MB9 Structure: Mordant Blue 9 y = 1.97E+00x + 1.09E+01 R2 = 0.97 240 160 [Zn2L1]/Abs 80 0 0 20 40 60 80 100 120 6 10 *[Zn2L1] Figure D-7. Titration of Mordant Blue 9 (MB9). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 251 MX Structure: Figure D-8. Titration of Murexide (MX). Benesi-Hildebrand plot of spectral data points 2 (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 252 PAR Structure: Figure D-9. Titration of 4-(Pyridin-2-ylazo)resorcinol (PAR). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 253 PV Structure: Figure D-10. Titration of Pyrocatechol Violet (PV). Benesi-Hildebrand plot of spectral data points (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R2 value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 254 ZC Structure: Figure D-11. Titration of Zincon (ZC). Benesi-Hildebrand plot of spectral data points 2 (blue diamonds) and the linear fit (black line) used to calculate Kd. The equation and R value for the linear fit are displayed in the upper right hand corner of the plot. This variation of the classic Benesi-Hildebrand method is based on a treatment described in reference S2 (note that slope does not equal Kd directly). 255 Appendix F CV spectra 256 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 Current(I) -0.4 -0.6 -0.8 -1.0 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 E vs (F /F +) c c Figure F-1. Cyclic voltammetry of PPE1. 257 1.0 0.5 0.0 -0.5 -1.0 Current(I) -1.5 -2.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 E vs (F /F +) c c Figure F-2. Cyclic voltammetry of PPE3. 258 2 0 -2 -4 Current(I) -6 -8 -10 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 E vs (F /F +) c c Figure F-3. Cyclic voltammetry of PF1. 259 0.0000015 0.0000010 0.0000005 0.0000000 -0.0000005 Current(I) -0.0000010 -0.0000015 -0.0000020 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 E vs (F /F +) c c Figure F-4. Cyclic voltammetry of PF3 260