Template Formation of Aza(Dibenzo)Dipyrromethenes and Structure and Electronics in Dimeric Boron Π Expanded Azine and Salphen Complexes

TEMPLATE FORMATION OF AZA(DIBENZO)DIPYRROMETHENES AND STRUCTURE AND ELECTRONICS IN DIMERIC BORON Π EXPANDED AZINE AND SALPHEN COMPLEXES

A Dissertation Presented to The Graduate Faculty at The University of Akron

In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy

Laura Crandall August, 2017 TEMPLATE FORMATION OF AZA(DIBENZO)DIPYRROMETHENES AND STRUCTURE AND ELECTRONICS IN DIMERIC BORON Π EXPANDED AZINE AND SALPHEN COMPLEXES

Laura Crandall

Dissertation

Approved: Accepted:

______Advisor Department Chair Dr. Christopher J. Ziegler Dr. Christopher J. Ziegler

______Committee Member Dean of the College Dr. Claire A. Tessier Dr. John C. Green

______Committee Member Dean of the Graduate School Dr. Wiley J. Youngs Dr. Chand Midha ______Date Committee Member Dr. Yi Pang ______Committee Member Dr. Li Jia

ii ABSTRACT

Template reactions have been known for over 100 years and have been employed to synthesize compounds that are difficult to obtain, to increase yield, and directly obtain the metal complex. After its fortuitous discovery in 1907 and again in 1927, phthalocyanine derivatives were mainly used as dye materials. In the latter half of the 20th century through the seminal work of Linstead and others, the metal chemistry of phthalocyanine was explored forming a rich history. In addition to exploiting the template formation of phthalocyanine, larger and smaller ions were used to form superphthalocyanine and subphthalocyanine, five and three isoindoline macrocycles respectively. Calcium has also been used to template the reaction of the isoindoline based macrocycle hemiporphyrazine and bis-arylisoindolne. While the template formation of isoindoline macrocycles is well explored, the template formation of isoindoline based chelates is largely unexplored.

The second and third chapters in this thesis present the template synthesis of

+ aza(dibenzo)dipyrromethenes, a “half phthalocyanine” like chelate, using Re(CO)3 or an aryl boron species to template the reaction in one step. In both cases, when water is present during the reaction, partial and full hydrolysis of the terminal group takes place. The spectroscopy and electrochemistry of these compounds was investigated, along with DFT and TDDFT calculations of the boron adducts. Organic fluorophore research has recently been focused on synthesizing compounds with high quantum yields of emission and a red

iii shifted absorbance for use in biological imaging, sensing, and organic electronic devices.

At the forefront of this research has been the BODIPY family of compounds, a dipyrromethene backbone coordinated to a central BF2 unit. In addition to BODIPYs, other boron based fluorophores have been synthesized in an effort to overcome some of the shortcomings in the photophysical properties of BODIPYs. The fourth chapter in this thesis describes the synthesis, structure, and electronic properties of boron azine and salphen complexes. DFT and TDDFT calculations were also conducted to gain further insight into the electronic properties of these complexes.

iv ACKNOWLEDGEMENTS

I would first and foremost like to say thank you to my advisor, Christopher J.

Ziegler. His support and guidance was instrumental in navigating my way through graduate school.

I would also like to thank my previous and current colleagues in the lab. Ingrid and

Kullapa- you took me in as your “lab child” my first years as a graduate student. I can’t thank you enough for everything you have taught me and all the support you have given me. Jim, Abed, Allen and Briana- your friendship, support, and collaboration on projects is greatly appreciated. I will be forever grateful for working in a collaborative environment where support was always available and disagreements were non-existant.

Thank you to the members of my committee: Dr. Claire Tessier, Dr. Wiley Youngs,

Dr. Yi Pang and Dr. Li Jia. I am grateful for your support and time spent serving on my committee. My acknowledgement goes to the University of Akron and the department of

Chemistry for accepting me into the program and financially supporting me during my

Ph.D. career.

Lastly I would like to thank my family (both blood and those who have taken me in as their own) for putting up with me through the ups and downs of graduate school, and for talking me out of quitting. Without their love and support during the hard times and help celebrating the good times, none of this would be possible.

v TABLE OF CONTENTS

LIST OF TABLES………………………………………………………………………..ix

LIST OF FIGURES………………………………………………………………………..x

LIST OF SCHEMES…………………………………………………………………….xiv

LIST OF ABBREVIATIONS…………………………………………………………...xvi

CHAPTER

I. INTRODUCTION AND BACKGROUND……………………………………………..1

1.1 Template Reactions……………………………………………………………1

Phthalocyanine………………………………………………………………...4

Superphthalocyanine…………………………………………………………13

Subphthalocyanine…………………………………………………………....15

Axial modification of SubPc………………………………………………….17

Peripheral modification of SubPc…………………………………………….20

Ring expansion to form phthalocyanine………….…………………………...21

The Hemiporphyrazines……………………………………………………….24

1.2 Luminescence………………………………………………………………..38

vi BF2 fluorophores: BODIPY Dyes……………………………………………44

Aza-BODIPY…………………………………………………………………49

BF2 complexes of 3,3’-diaryldiisoindolylmethene…………………………..54

Aza-(dibenzo)dipyrromethene………………………………………………...55

Bis Boron fluorophores………………………………………………………..57

BOPHY………………………………………………………………………..59

II. RE(CO)3 TEMPLATED FORMATION OF AZA(DIBENZO)DIPYRROMETHENES………………………………………………71 Introduction…………………………………………………………………...71

Experimental………………………………………………………………….74

Results and Discussion……………………………………………………….83

Conclusion……………………………………………………………………88

III. BORON TEMPLATED SYNTHESIS OF A BODIPY ANALOGUE FROM A PHTHALOCYANINE PRECURSOR…...………………………………………………89 Introduction…………………………………………………………………...89

Experimental………………………………………………………………….91

Results and Discussion……………………………………………………….98

Conclusion…………………………………………………………………..107

IV. STRUCTURE AND ELECTRONICS IN DIMERIC BORON Π EXPANDED AZINE AND SALPHEN COMPLEXES…….…...……………………………………………..108 Introduction………………………………………………………………….108

vii Experimental………………………………………………………………...111

Results and Discussion……………………………………………………...121

Conclusion…………………………………………………………………..129

V. SUMMARY…………………………………………………………………………130

REFERENCES…………………………………………………………………………132

APPENDIX A: SOLVATOCHROISM OF COMPOUNDS 2-7………………………164

APPENDIX B: PERMISSIONS………………………………………………………..168

viii LIST OF TABLES

1.2.1: Absorbance and emission data for 1a-c and 2a-c in dioxane……………………….67 1.2.2: Quantum yields of singled oxygen generation for several BOPHY compounds...... 68 2.1: Crystal data and structure refinement for 2.2……………….……………………….78 2.2: Crystal data and structure refinement for 2.4………………………………………..79 2.3: Crystal data and structure refinement for 2.5………………………………………..80 2.4: Crystal data and structure refinement for 2.6………………………………………..81 2.5: Crystal data and structure refinement for 2.7………………………………………..82 3.1: Crystal data and structure refinement for 3.1………………………………………..95 3.2: Crystal data and structure refinement for 3.2………………………………………..96 3.3: Crystal data and structure refinement for 3.3………………………………………..97 4.1: Crystal data and structure refinement for 4.1………………………………………116 4.2: Crystal data and structure refinement for 4.2………………………………………117 4.3: Crystal data and structure refinement for 4.3………………………………………118 4.4: Crystal data and structure refinement for 4.4………………………………………119 4.5: Crystal data and structure refinement for 4.5………………………………………120 4.6: Selected absorption and emission parameters for compounds 4.1-4.5…………….125

ix LIST OF FIGURES 1.1.1: Solid state structure of cyclam (1,4,8,11-tetraazacyclotetradecane) free base with intramolecular hydrogen bonds (left) and intermolecular hydrogen bonds (right) shown in blue………………………………………………………………………………………...2 1.1.2: Metal free phthalocyanine (left) and metal free porphyrin (right)…………………...5 1.1.3: Common starting materials for PC synthesis……………………………………….6 1.1.4: Template synthesis of Pc……………………………………………………………6 1.1.5: Nickel (II) phthalocyanine. Top view (left) and side view (right)…………………...7 1.1.6: α and β positions on the phthalocyanine macrocycle………………………………..8 1.1.7: Uv-visible spectra of Pc and NPcs in THF…………………………………………..9 1.1.8: Four possible positional isomers of 1,8(11),15(18),22(25)-tetrasubstituted Pcs…...10 1.1.9: Bis(Phthalocyanato)-lutetium(III). Top view (left) and side view (right)………….13 1.1.10: Crystal structure of superphthalocyanine. Top view (top) and side view (bottom).14 1.1.11: Chloro-SubPc. Top view (left) and side view (right)……………………………..16 1.1.12: UV-visible spectrum of Cl-SubPc (bold line) and NiPc (thin line)……………….17

1.1.13: Coordinatively unsaturated SubPc with CHB11Me5 Br6 anion……………………20

1.1.14: C1 (left) and C3 (right) isomers of triiodo SubPc…………………………………21

1.1.15: Ring expansion of SubPc to make A3B Pc………………………………………..22 1.1.16: Reaction conditions for the synthesis of A3B 2,3-dipropoxy phthalocyanine from SubPc…………………………………………………………………………………….23 1.1.17: 1,3-bis(arylimino)isoindoline……………………………………………………25 1.1.18: Examples of various hemiporphyrazines………………………………………...25 1.1.19: Crystal structures of anhydrous bis-pyridyl hemiporphyrazine (top) and monohydrate (bottom, side view left, top view right)…………………………………….27

x 1.1.20: Top (top left) and side view (top right) of free base dicarbahemiporphyrazine crystallized with dimethylsulfoxide and the dication of dicarbahemiporphyrazine (top view bottom left, side view bottom right)………………………………………………………28 1.1.21: Modified dicarbahemiporphyrazines……………………………………………..30 1.1.22: UV-visible spectrum of bis-pyridylhemiporphyrazine in dimethylformamide…...31 1.1.23: Uv-visible spectrum of dicarbahemiporphyrazine 1 and 2………………………..32 1.1.24: Ni(II) bis-pyridyl hemiporphyrazine. Top view (left) and side view (right)...... 33 1.1.25: Ag(I) dicarbahemiporphyrazine (left) and Cu(II) dicarbahemiporphyrazine (right)…………………………………………………………………………………….35 1.1.26: Ni(II) dchp (top) and Pt(II) dchp (bottom)………………………………………..37 1.2.1: Simplified Jablonski Diagram……………………………………………………..39 1.2.2: Structures of common fluorophores…………………………………………...... 41 1.2.3: Protonation states of fluorescein…………………………………………………...42 1.2.4: 4-methyl-7-hydroxycoumarin……………………………………………………..43 1.2.5: BODIPY core with numbering (left) and crystal structure of unsubstituted BODIPY (right)…………………………………………………………………………………….44 1.2.6: Cyanine (left), rigified cyanine (middle left), s-indicine (middle right) and BODIPY core (left)…………………………………………………………………………………45 1.2.7: Palladium cross coupling reactions of BODIPY…………………………………...48 1.2.8: Absorption and emission data for various BODIPY substitution patterns…………49 1.2.9: Aza-BODIPY core………………………………………………………………...50 1.2.10: First aza-BODIPYS tested as PDT agents………………………………………..50 1.2.11: Crystal structure of aza-BODIPY 2b……………………………………………..51 1.2.12: Absorbance (black line) and emission spectra (gray line) for BODIPY A and aza- BODIPY B……………………………………………………………………………….52

1.2.13: Crystal structure of the BF2 complex of aza-(dibenzo)dipyrromethene…………..57

1.2.14: Structures, absorbance, and emission data of some bis BF2 fluorophores………...58 1.2.15: Bimetallic boron complexes of salen (left) and N,N’-p- phenylenebis(salicylideneimine)…………………………………………………………59

1.2.16: Crystal structure of Me4BOPHY…………………………………………………61

xi 1.2.17: Modified BOPHY adducts and their absorbance and emission data in dichloromethane………………………………………………………………………….62 1.2.18: Normalized UV-vis (top left) and emission spectra (top right) of 4-N,N- dimethylbenzyl monostyryl-BOPHY in solvents of varying polarity and the absorbance spectra (bottom left) and emission spectra (bottom right) after the addition of HCl………64 1.2.18: Thienyl appended BOPHY (left) and bis-ferrocene BOPHY (right)……………..65 1.2.19: BOPHY complexes tested for triplet–triplet annihilation upconversion and singlet oxygen production………………………………………………………………………..68

1.2.20: Crystal structures of BPh2BOPHY (left) and BPh2 Me4BOPHY (right)…………70 2.1. Templated synthesis of aza(dibenzo)dipyrro-methenes……………………………...73 2.2: The crystal structures of 2.2-2.7 with 35% thermal ellipsoids………………………84 2.3: Uv-Visible spectra of 2.2-2.4 in dichloromethane……………..…………………….86 2.4: Uv-Visible spectra of 2.5-2.7 in dichloromethane……………………………..…….86 2.5: Cyclic volatmmograms of compounds 2.2-2.4 in DMF………………………….….87 2.5: Cyclic volatmmograms of compounds 2.5-2.7 in DMF………………………….….88 3.1: The structures of BODIPY (left) and aza-BODIPY (right)…………………………..90 3.2: The crystal structures of 3.2-3.7 with 35% thermal ellipsoids………………………99 3.3: The normalized absorption (left) and emission (right) spectra for compounds 3.1-3.3 in acetonitrile……………………………………………………………………………101 3.4: Cyclic voltammongrams of 3.1, 3.2, and 3.3 in 0.1 M TBAPF6/acetonitrile at 0.25 V/s and 10.0 μA V−1 versus AgCl…………………………………..………………………102 3.5: Frontier orbital diagrams for 3.1.…………………………………………………...103 3.6: Orbital compositions for 3.1.……………………………………………………….104 3.7: Frontier orbital diagrams for 3.2…………………………………………………...104 3.8: Orbital compositions for 3.2.……………………………………………………….105 3.9: Frontier orbital diagrams for 3.3.…………………………………………………...105 3.10: Orbital compositions for 3.3.……………………………………………………...106 3.11: DFT-predicted orbital energies of compounds 3.1-3.3…………………………....106 3.12: Experimental and TDDFT-predicted UV-vis spectra of compounds 3.1 (left top), 3.2 (left bottom) and 3.3 (right)……………………………………………………………..107 4.1: Azine, π expanded azine and π expanded salphen BF2 complexes………………...110

xii 4.2: The crystal structures of 1-5 with 35% thermal ellipsoids………………………….123 4.3: Normalized absorption (solid line) and emission (dotted line) spectra of 1 and 2 in acetonitrile. Compounds were excited at the lowest energy maxima for emission spectra…………………………………………………………………………………..124 4.3: Normalized absorption (solid line) and emission (dotted line) spectra of 3-5 in acetonitrile. Compounds were excited at the lowest energy maxima for emission spectra…………………………………………………………………………………..125 4.5: DFT predicted (TPSSh functional / 6-311G(d) basis set) frontier orbital energy levels for 1-5…………………………………………………………………………………...126 4.6: DFT predicted frontier orbital structures for 1-5……………………………………128 4.7: Observed and calculated Uv-visible spectra for 1-5………………………………...129

xiii

LIST OF SCHEMES 1.1: Synthesis of 1,4,8,11-tetraazacyclotetradecane (cyclam)……………………………..2 1.1.2: Synthesis of Ni(II) 1,4,8,11-tetraazacyclotetradecane from Ni(II) ethylenediamine and acetone………………………………………………………………………………...3

1.1.3: Template synthesis of a N2S2 macrocycle…………………………………………...4 1.1.4: Products from statistical condensation reaction of two phthalonitriles…………….11 1.1.5: Projected cyclotetramerization raction (top) and actual cyclopentamerization reaction (bottom)…………………………………………………………………………13 1.1.5: The synthesis of Chloro-SubPc……………………………………………………15 1.1.6: Synthesis of axially substituted SubPcs with Grignard reagents…………………...18 1.1.7: Proposed mechanism of the formation of phenol substituted SubPc from Cl- SubPc…………………………………………………………………………………….19

1.1.8: CaCl2 templated synthesis of hemiporphyrazine and BPI…………………………26 1.1.9: Synthesis of 18 π-electron aromatic dicarbahemiporphyrazine (2) from dicarbahemiporphyrazine 1………………………………………………………………31 1.2.1: Synthesis of symmetric BODIPY from pyrroles and an aldehyde…………………45 1.2.2: Synthesis of BODIPY from ketopyrroles………………………………………….46 1.2.3: Halogenation of BODIPY core…………………………………………………….47 1.2.4: Synthesis of ADPM from 5-nitroso pyrrole………………………………………..53 1.2.5: Synthesis of ADPM from chalcones……………………………………………….53 1.2.6: Synthesis of 3,3’-diaryldiisoindolylmethene (top) and the Cu(II) complex of 3,3’- diaryldiisoindolylmethene………………………………………………………………..54 1.2.7: Synthesis of difluoroboryl complexes of 3,3’-diaryldiisoindolylmethene…………55 1.2.8: First synthesis of aza-(dibenzo)dipyrromethene…………………………………...56

1.2.9: Synthesis of unsubstituted and Me4BOPHY……………………………………….60

1.2.10: Knovenagel condensation of Me4BOPHY with 4-N,N-dimethylbenzadeldehyde to form 4-N,N-dimethylbenzyl monostyryl-BOPHY……………………………………….62

xiv

1.2.11: Synthesis of bis-styryl 4-ethynylperylene BOPHY………………………………66 1.2.12: Synthesis of mono and bis ethynyl BOPHYs 1a-c and 2a-c………………………66 3.1: The reaction to form compounds 3.1-3.3..…………………………………………...90 4.1: Synthesis of compounds 4.1-4.5…..………………………………………………..112

LIST OF ABBREVIATIONS

Pc- phthalocyanine Cyclam- 1,4,8,11-tetraazacyclotetradecane DII- 1,3-diiminoisoindoline SuperPc- superphthalocyanine SubPc- subphthalocyanine dchp- dicarbahemiporphyrazine BODIPY- boron dipyrromethene NBS- N-bromosuccinimide NCS- N-chlorosuccinimide Aza-BODIPY- boron azadipyrromethene TBTAB- tetrabenzotriazaporphyrin ADBM- aza-dibenzodipyrromethene BOPHY- bis(difluoroboron)1,2-bis((pyrrol-2-yl)methylene)hydrazine

DCM/ CH2Cl2- dichloromethane DMSO- dimethylsulfoxide DMF- dimethylformamide MLCT- metal-to-ligand charge transfer

TBAPF6-tetrabutylammonium hexafluorophosphate LUMO- lowest unoccupied molecular orbital HOMO- highest occupied molecular orbital

xvi

CHAPTER I INTRODUCTION AND BACKGROUND

1.1 Template Reactions

Although examples of template reactions have been known for over a century, the term “template reaction” was not defined in the literature until 1964 by Thompson and

Busch. A template reaction is described as a reaction in which an ion holds reactive groups within a substitution-inert complex in proper geometric arrangement to facilitate a stereochemically selective multistep reaction.1,2 Although in some cases a compound can form without a template present, it is often preferred to synthesize the desired product through a template reaction to increase yield, to directly obtain a metal complex, and to run the reaction under mild conditions.3,4 In a template reaction, small molecules coordinate to a central atom or molecule, often a metal center, arranging them in a geometrically prefixed manner. After initial coordination, the geometry allows ligand to form.1,3,4 The pre- arrangement of reactants around a metal center can speed up reaction times because they are located in close proximity to each other and can react in an intramolecular fashion. Two of the earliest observed template reactions were the syntheses of cyclam, a tetraazine macrocycle, and phthalocyanine (Pc).3,4

1,4,8,11-Tetraazacyclotetradecane, also known as cyclam, was first synthesized in

1937 by van Alphen based on the reaction of 1,3-dibromopropane with ethylene diamine in the presence of an alkali metal cation (Scheme 1.1.1).5 This reaction was uncovered

1 while working on the synthesis of alkylated ethane diamine and tri-ethylene tetramine derivatives.4–6 In its neutral form, cyclam adopts an endodentate conformation (Figure

1.1.1), where two opposite NH groups form an intramolecular hydrogen bond across the center of the macrocycle. The other two NH groups are pointed in opposite directions, perpendicular to the plane of the macrocycle, forming intermolecular hydrogen bonds.7 It was not until 1965 that Bosnich, Poon, and Tobe reported the first metal cyclam complexes.8

Scheme 1.1: Synthesis of 1,4,8,11-tetraazacyclotetradecane (cyclam).5

Figure 1.1.1: Solid state structure of cyclam (1,4,8,11-tetraazacyclotetradecane) free base with intramolecular hydrogen bonds (left) and intermolecular hydrogen bonds (right) shown in blue. Gray, light blue, and white spheres represent carbon, nitrogen and hydrogen atoms respectively. All non-ionizable hydrogens have been removed for clarity.7

Presenting chemistry similar to that of cyclam, Curtis reported that tris(ethylenediamine)nickel (II) perchlorate would react to form yellow macrocyclic Schiff base products when stirred in dry acetone at room temperature (Scheme 1.1.2, top) 9 It was later found that a cyclization had occurred, and the product shown in the bottom of Scheme

1.1.2 was formed during the reaction.4,10

Scheme 1.1.2: Synthesis of Ni(II) 1,4,8,11-tetraazacyclotetradecane from Ni(II) ethylenediamine and acetone.11 In 1964, Thompson and Busch reported the reaction of a divalent nickel halide salt with β-mercaptoethylamine followed by the addition of an α-diketone which resulted in the formation of a Schiff base chelating ligand. Previous attempts to isolate α-diimines through non-template synthesis methodologies resulted in either extremely low yields or in the formation of thiazolines.12 To fully test their template method, Thompson and Busch reacted nickel (II) α-diketobismercaptoethylimine with the difunctional alkylating agent

α,α′-dibromo-o-xylene to form a macrocycle where the nitrogen and sulfur atoms are coordinated to the Ni(II) center (Scheme 1.1.3).2 Through the 1960s and early 1970s,

Busch, Curtis, and others published many synthetic reports using the template method to synthesize previously difficult to obtain products.2,9,10,12–17

2,12 Scheme 1.1.3: Template synthesis of a N2S2 macrocycle.

Phthalocyanine

One of the earliest examples of a template reaction is the synthesis of phthalocyanine (Pc). Phthalocyanine was accidentally discovered in 1907 as an insoluble blue side product during the reaction of acetic anhydride and phthalimide in a cracked reaction vessel.18 The same insoluble blue product was later reported in 1927 by de

Diesbach and von der Weid following the reaction of ortho-dibromobenzene and copper cyanide.19 While the lack of solubility made the unknown product difficult to characterize, this blue material was an ideal candidate for dye applications. In 1928, Scottish Dyes Ltd. filed a patent on phthalocyanine for its development as a colorant.20 To further probe the structure of phthalocyanine, a sample was given to R.P. Linstead at Imperial College,

London. Linstead worked on synthetic methods and correctly predicted the structure of phthalocyanine in a series of reports in 1934.21–25 The structure was confirmed by J.

Moneath Robertson a year later via X-ray crystallography.26 Unsubstituted phthalocyanine

(Figure 1.1.2, left) is an 18π- electron aromatic macrocycle that is composed of four isoindoline units linked via bridging nitrogen atoms and is structurally similar to porphyrin

(Figure 1.1.2, right). 27

Figure 1.1.2: Metal free phthalocyanine (left) and metal free porphyrin (right).

Phthalocyanines can be synthesized from a variety of starting materials, as shown in Figure 1.1.3. In most reactions, the starting reagent is refluxed with a transition metal salt in a high boiling point solvent. Phthalonitrile and 1,3-diiminoisoindoline (DII) are the two most common precursors.27 Figure 1.1.4 shows the template reaction of phthalocyanine from DII with a divalent metal cation ion as the template. After an initial dimerization of diiminoisoindoline, the indole nitrogen atoms of the two resultant dimers coordinate to a metal, bringing them into close enough proximity to allow for the formation of the macrocycle.27

Figure 1.1.3: Common starting materials for PC synthesis.27

Figure 1.1.4: Template synthesis of Pc.27

When characterizing metallated phthalocyanines, Linstead and Robertson noted that the BeII, MnII, FeII, CoII, NiII, and CuII structures (Figure 1.1.5) all retained a square planar geometry with the metal ion residing in the core of the Pc macrocycle. The macrocycle can distort to allow ions of varying radii to fit into the central cavity.26,28,29

When metallated with the larger transition metal ion PtII, it was discovered that the macrocycle has a ~44° bend, showing that the Pt atom resides above the plane of the macrocycle.29

Figure 1.1.5: Nickel (II) phthalocyanine. Top view (left) and side view (right). Gray, light blue, and green spheres represent carbon, nitrogen and nickel atoms respectively. Hydrogen atoms have been removed for clarity.29 Both the metal free and metallated Pcs have strong Q-band absorbances in the visible region of the electromagnetic spectrum between 650 and 670 nm with extinction coefficients of ~105 M-1cm-1.30–33 Their absorbance spectra can undergo either bathochromic or hypsochromic shifts depending on the identity of the metal ion and the substitution on the benzene ring of the isoindoline. In addition to shifting the absorbance spectrum, when the macrocycle is asymmetric, the Q-band can split. When metallated with a closed shell metal cation such as Li(I), Mg(II), or Zn(II), the absorbance maxima is ~670 nm.30–35 When metallated with an open shell cation such as Fe(II), Co(II), or Ru(II), the Q-

7 band is blue shifted to ~630-650 nm.32,33,35,36 When substituted at the β position (Figure

1.1.6) with eleactron withdrawing substituents such as sulfonyl, carboxyl, or fluorinated groups, the Q-band has a tendency to shift bathochromically.31,32 When substituted with electron donating subsitutents such as amino, alkoxy and alkyl groups, there is a negligible effect on the absorption spectra.31,32

Figure 1.1.6: α and β positions on the phthalocyanine macrocycle.

When substituted with either electron withdrawing or electron donating groups at the α positions, the shift in the absorbance spectrum follows the same trend as the β positions; however, it is more pronounced.31,32,37 In addition to adding substituent groups at the α and β positions, extension of the π system and lowering the symmetry of the macrocycle also shifts the absorbance spectra to the red.38–43 In π extended naphthalocyanine (NPcs) there is a 20-30 nm red shift in the Q-band per each additional benzene ring (Figure

1.1.7).38–40

Figure 1.1.7: Uv-visible spectra of Pc and NPcs in THF.40 (Figure reprinted with permission from Inorg. Chem. 2012, 41 (21), 5350–5363 Copyright © 2002 American Chemical Society) The electronic properties of phthalocyanines can be easily modulated by varying the substituent groups on the α and β positions as well as lowering the symmetry of the macrocycle. Substituted phthalocyanines can be synthesized two ways: By using a modified starting material with a particular functional group, or by aromatic electrophilic substitution reaction post cyclotetramerization, including halogenation followed by palladium catalyzed coupling reactions.27,44–48 When condensing a modified starting material to make a Pc, positional isomers that are difficult to separate are formed (Figure

1.1.8) if the starting material is not substituted symmetrically.44,49–52 To synthesize phthalocyanines of lower symmetry, a statistical condensation can be employed, where dinitriles with different substituents are condensed, resulting in a mixture of products

(Scheme 1.1.4).53

Figure 1.1.8: Four possible positional isomers of 1,8(11),15(18),22(25)-tetrasubstituted Pcs.44

Scheme 1.1.4: Products from statistical condensation reaction of two phthalonitriles.53

In 1988, and 1990, Ando, Mori,54,55 and, in a separate report, Kobayashi56 reported the ring expansion reaction of subphthalocyanine, reacting SubPc with one equivalent of 1,3- diiminoisoindolne as a relatively high yield and selective method to form A3B phthalocyanines. The ring expansion reaction of SubPc will be discussed in depth later in this chapter.

With new synthetic methods and better purification methods, phthalocyanines have become easily modifiable materials for applications beyond their traditional uses as

11 dyes. Modulation of the electronic, physical, and optical properties has allowed for its use in photovoltaics and light harvesting devices,31,57–59as a photosensitizers for photodynamic therapy,60–64 printing materials,65 sensors,66–69 catalysts,60,70–72 biological imaging regents,73,74 non-linear optics,75–78 polymers, and liquid crystal applications.79–84

In addition to varying the exterior of the phthalcyanine ring, more than 60 metal ions can be inserted into the central cavity to optimize their properties.31,57

After the initial synthesis of Pc with transition metal ions, ions from other areas of the periodic table were soon used as templates in effort to develop phthalocyanines with novel properties. However, some reactions resulted in alternate structures. In the 1960s, the uranyl cation was investigated as a template, resulting in a cyclopentamerization, forming superphthalocyanine (vide infra).32,85,86 In the early 1970s, Kirin and coworkers reported the reaction of phthalonitrile with lanthanide cations formed a sandwich complex where two phthalocyanine rings would coordinate to a single rare-earth cation

(Figure 1.1.9).18,87–90 When templating the reaction with the small boron (III) cation,

Meller and Ossko found that a cyclotrimerization occurs, forming subphthalocyanine

(vide infra).91,92

Figure 1.1.9: Bis(phthalocyanato)-lutetium(III). Top view (left) and side view (right). Gray, light blue, and green spheres represent carbon, nitrogen, and luteium respectively. Hydrogen atoms have been removed for clarity.93 Superphthalocyanine

When the large uranyl cation is used to template the condensation of phthalonitrile, a 22 π electron aromatic superphthalocyanine (SuperPc) is formed. Uranyl superphthalocyanine was first prepared in 1964 by Bloor and coworkers by the condensation of phthalonitrile around the uranyl cation in dry dimethyl formamide

(Scheme 1.1.5).85

Scheme 1.1.5: Projected cyclotetramerization raction (top) and actual cyclopentamerization reaction (bottom)

In comparison to known metallated Pc, the absorbance spectrum of the assumed cyclotetramerization product shifted from 665 nm (ZnPc) to 910-940 nm.43 The authors of the initial report on this compound attributed the significant red shift to interactions of the

Pc orbitals and the uranium orbitals.85 It was not until 1975 that the true structure of uranyl superPC was correctly determined by Day and coworkers upon elucidation of the structure by X-ray crystallography (Figure 1.1.10).86 Unlike phthalocyanine, superphthalocyanine is buckled rather than planar in structure and the uranyl cation adopts pentagonal bipyramidal geometry.

Figure 1.1.10: Crystal structure of superphthalocyanine. Top view (top) and side view (bottom).Gray, light blue, red, and blue spheres represent carbon, nitrogen, oxygen, and uranium respectively. Hydrogen atoms have been removed for clarity. 94

In the mid-1970s, it was discovered that superPC could undergo a ring contraction to form metal phthalocyanine in high yield when refluxed in dry dimethyl formamide with a metal chloride or metal acetate.94,95 SuperPc has neither been made with cations other than uranium, nor has evidence of the de-metallated macrocycle been found. These factors, coupled with its low solubility limits the uses for this macrocycle.96

Subphthalocyanine

In 1972, Meller and Ossko carried out a reaction using BCl3 to template the formation of boron phthalocyanine using phthalonitrile as the precursor.91,92 Instead of the expected blue product, a fuchsia product was observed. After analysis, the results showed that a cyclotetramerization had not taken place, but the small size of the boron atom allowed for a cyclotrimerization of phthalonitrile (Scheme 1.1.5). Whereas phthalocyanines are planar 18 π-electron aromatic systems, SubPcs comprise 14 π-electron aromatic systems that are bowl shaped with the boron center sitting above the plane of the three isoindole nitrogen atoms (Figure 1.1.11).43,92,97,98 Little work was done on the chemistry of subphthalocyanines until the early 1990s when Kobayashi used SubPc as a synthon for the synthesis of asymmetric phthalocyanines. 43,56

Scheme 1.1.5: The synthesis of chloro-SubPc.92

Figure 1.1.11: Chloro-SubPc. Top view (left) and side view (right). Gray, light blue, pink, and green spheres represent carbon, nitrogen, boron, and chlorine respectively. Hydrogen atoms have been removed for clarity.99 The absorbance spectrum of SubPc is hypsochromically shifted in comparison to phthalocyanine, and the extinction coefficients of these compounds are smaller (5-6 x 104

M-1cm-1 for SubPc, 8-24 x 104 M-1cm-1 for Pc, Figure 1.1.12). This can be attributed to the non-planar nature of SubPc. The SubPc core is robust and can tolerate post synthetic modifications at both the axial position and on the periphery. Substitution of the exterior of SubPc tends to red shift the absorbance spectrum. The exchange of the axial group has little to no effect on the energy of UV-visible absorption, however.92,98,100,101 Ring expansion reactions are an easy method to obtain A3B type phthalocyanines, which can be difficult to obtain through traditional synthetic routes.54,55,92,98,102

Figure 1.1.12: UV-visible spectrum of Cl-SubPc (bold line) and NiPc (thin line).98 (Figure reprinted with permission from Chem. Rev. 2002, 102 (3), 835–854. Copyright © 2012 American Chemical Society) Axial modification of SubPc

Axial modification is one of the easiest methods to incorporate SubPc into more complex molecular sytems.92,103104 The first example of modifications at the axial position was replacing the halogen with a phenyl ring. The synthesis of SubPcs with an axial phenyl ring was first reported by Hanack in 1994 and was accomplished by refluxing triphenylborane with phthalonitrile in naphthalene with a stoichiometric amount of 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU).105 A few years later, Torres, Hannack, and coworkers reported the replacement of an axial chloride with a phenyl ring. Upon reacting substituted phthalonitriles or DII with triphenylborane, only a small amount of product forms unless the super base 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-

5 5 bis[tris(dimethylamino)-phosphoranylidenamino]-2λ ,4λ -catenadi(phosphazene) (P4-t-

Bu) was present in catalytic amounts. Products formed with yields of ~15-20%. To increase the yield, Torres and Hannack synthesized peripherally substituted Cl-SubPc and reacted it with an excess of phenyllithium at -70ᵒC to afford the Ph-SubPc in ~17% yield.106

A similar procedure was also reported by Potz in 2000.97 In 2008, Ziessel presented arylethynyl-substituted SubPcs through the reaction of Cl-SubPC with Grignard reagents.107 More recently, Bender et al. reported the synthesis of a series of phenyl substituted SubPcs with para substituents (Scheme 1.1.6), based Ziessel’s 2008 report.101,107

Scheme 1.1.6: Synthesis of axially substituted SubPcs with Grignard reagents.101

The most common axial substitution is the replacement of the halide with alcohols, forming boronic esters.92,100,104 The first report of a SubPc boronic ester appeared in 1996 by Kasuga et al. The alkoxy and phenoxy SubPcs were synthesized by refluxing the appropriate alcohol with Br-SubPC. 108 In 2002, Potz and coworkers reacted carboxylic acids with Br-SubPc, finding that they react more readily than alcohols.97 Whereas the reaction of alcohols with SubPc has been known for over 20 years, the mechanism was not proposed until 2014 by Torres et al. 103 The proposed mechanism is shown in Scheme 1.1.7.

Scheme 1.1.7: Proposed mechanism of the formation of phenol substituted SubPc from Cl- SubPc.103

In the proposed mechanism, a phenol approaches the subPc and the proton hydrogen bonds to the chloride to form an intermediate where the B-Cl bond is lengthened. In the proposed transition state (TS), the B-Cl and O-H σ bonds are broken and the B-O and H-Cl bonds are formed concertedly. After bond formation, the hydrogen from the HCl remains coordinated to the oxygen through hydrogen bonding (Prod2), dissociating to form the phenoxy-SubPc (Prod1) and HCl.

Few other examples of axial substitutions have been reported. In 2006, Kato et al. reported the synthesis and crystal structure of a coordinatively unsaturated SubPc with a weakly coordinating anion, shown in Figure 1.1.13.109 Similar to Kato’s work, Torres and coworkers presented the synthesis of a SubPc with an axial triflate (OTf) in a two-step, one-pot reaction as an intermediate for substitution reactions of nucleophiles containing

19 oxygen, sulfur, nitrogen, or carbon.110 The triflate intermediate was synthesized by stirring silver triflate at 20ᵒC or refluxing trimethylsilyl triflate with Cl-SubPc to irreversibly remove the chloride. After the formation of the OTf-SubPc intermediate, a nucleophile and

N-ethyldiisopropylamine (DIPEA) are both added to the reaction mixture to synthesize a variety of axially substituted products. In 2017, Wang and Fu isolated the OTf-SubPc intermediate and explored its reactivity with ethers, amides, and ketones.111 In 2012,

Bender et al. used AlCl3 to activate the B-Cl bond followed by nucleophilic substitution at the axial position.112

Figure 1.1.13: Coordinatively unsaturated SubPc with CHB11Me5 Br6 anion. Gray, light blue, pink, and bronze spheres represent carbon, nitrogen, boron, and bromine respectively. Hydrogen atoms have been removed for clarity.109 Peripheral modification of SubPc

Peripheral modification of SubPc can be defined as any modification to the indole rings and axial substituents (leaving the B-X bond intact). Due to the inherent instability of SubPc, the method used for peripheral modification must be carefully selected to avoid decomposition of the macrocycle.92,98 Palladium catalyzed cross coupling reactions such

20 as Sonogashira,107,113–123 Suzuki, 123–130 and Stille 127,131 transformations are often used for

C-C bond formation, starting from the mono or diiodo-substituted phthalonitrile. In the case of the tri-iodo SubPc, the C1 and C3 isomers (Figure 1.1.14) can be isolated via

HPLC.132 The periphery can also be modified via Buchwald-Hartwig amination 127,133,134 and borylation.127 Water soluble SubPcs have been synthesized by the conversion of tertiary amines into quaternary salts through alkylation reactions, 135–137 or the addition of sulfonate salts. 135,137138 Acylation reactions have been used to form water soluble products139 and ester functionalization.124,128,139 Cyclopropanation and 1,3-dipolar cyclo- addition reactions have also been used to append C60 fullerene to SubPc to study photoinduced processes in the resultant conjugates.117,124,125,133,134,140–143

132 Figure 1.1.14: C1 (left) and C3 (right) isomers of triiodo SubPc.

Ring expansion to form phthalocyanine

Prior to 1990, there were few reports of asymmetric phthalocyanines due to the difficulties encountered in synthesis and purification. Two reports by Ando and Mori 54,55 in 1988 and 1990 and one by Kobayashi in 1990 presented the ring expansion of SubPc to form phthalocyanine (Figure 1.1.15).56 Tri-tert-butylated SubPc was reacted with an equivalent of modified DII in a solution of DMF and either chlorobenzene, o-

21 dichlorobenzene, 1-chloronaphthalene, or 2-chloronaphthalene in a 2:1 ratio. Kobayashi showed that the ring expansion method was a facile way to synthesize metal free A3B Pc.

92,98,102

56 Figure 1.1.15: Ring expansion of SubPc to make A3B Pc.

In 1992, Kasuga and coworkers reported the sensitivity of SubPc ring expansion to the solvent used in the reaction. When synthesizing the A3B dipropoxy derivative of phthalocyanine (Figure 1.1.16), the SubPc decomposed and there was no formation of the asymmetric A3B product if reacted in DMSO. When reacted in pure chloronapthalene, octapropoxy phthalocyanine was formed. When reacted in 1:2 DMSO:chloronapthalene, the desired 2,3-dipropoxyphthalocyanine was formed.144

solvent conditions result DMSO decomposition of SubPC

chloronaphthalene formation of octapropoxy Pc

DMSO: chloronaphthalene (1:2) formation of 2,3- dipropoxy phthalocyanine Figure 1.1.16: Reaction conditions for the synthesis of A3B 2,3-dipropoxy phthalocyanine from SubPc.144

In 1995, Torres et al. described the differences in reactivity of 1,3- diiminoisoindoline derivatives. When 5-amino-1,3-diiminoisoindoline was refluxed with

SubPc in N,N-dimethylaminoethanol a mixture of monoamino phthalocyanine and unsubstituted Pc was formed. The reaction of SubPc with 5-nitro-1,3-diiminoisoindoline resulted in the formation of mononitro Pc along with a statistical mixture of phthalocyanines with zero, two, three, and four nitro groups regardless of the solvent system used in the reaction.145 Soon after, Wöhrle and coworkers reported an improved method for the ring expansion of SubPc by using Zn(II) as a template in the reaction to afford the metallated monosubstituted adduct in a one pot reaction. The monosubstituted

Pc was formed in >40% yield, with unsubstituted Pc formed in >50%, and the di, tri, and

23 tetra substituted Pc’s were formed in <10%.146 Since the initial reports in the early 1990s, there have been several reports on the synthesis of A3B phthalocyanines via a ring expansion from SubPc; however, the statistical condensation method is still employed.147–

158

Due to their relative ease of synthesis and modification, SubPcs have become versatile compounds where the physical properties can be easily changed for desired applications as well as facile incorporation into modular systems. Similar to the chemistry seen with SuperPc, only one cation,(B(III)), can template formation of SubPc. The ease of modification allow for use as photodynamic therapy agents,136,159 biological imaging,137,139 models for active sites in enzymes,160 artificial photosynthesis systems,113 sensors,161,162 and photovoltaics.104,126,142

The Hemiporphyrazines

In addition to investigating the synthesis of phthalocyanines, Linstead and coworkers synthesized modified phthalocyanines in the early 1950s by reacting DII with either monoamines to synthesize bis-aryl modified DIIs (Figure 1.1.17) or diamines (2,6- diaminopyridine, 1,3-diaminobenzene, 2,7-diaminonapthalene, 2,8-diaminoacridine, and

3,5-diaminopyridine) to form compounds later called hemiporphyrazines (Figure 1.1.18).

Like phthalocyanine, hemiporphyrazine is a four unit macrocycles where two opposite facing DII units or a single DII unit have been replaced with an alternate ring.

Hemiporphyrazines are 20 π-electron macrocycles, and unlike phthalocyanine, they are not aromatic.34,163–168

Figure 1.1.17: 1,3-bis(arylimino)isoindoline.

Figure 1.1.18: Examples of various hemiporphyrazines.34

In the 1970s, W.O. Siegl used calcium chloride to template the reaction of diamines or monoamines with phthalonitrile to synthesize metal free 1,3-bis(arylimino)isoindoline and hemiporphyrazine (Figure 1.1.19) from the monoamines and diamines respectively.34,169,170

While many diamines have been incorporated into the hemiporphyrazine, bis-pyridyl hemiporphyrazine has received the most attention.34

169 Scheme 1.1.8: CaCl2 templated synthesis of hemiporphyrazine and BPI.

In the solid state, bis-pyridylhemiporphyrazine is planar when there are no other molecules in the crystal lattice. When a single molecule of water co-crystallizes, the macrocycle adopts a saddle conformation (Figure 1.1.20).34,171,172 The water molecule in the hydrated hemiporphyrazine hydrogen bonds to the nitrogen atoms of the pyridine rings and the isoindoline units, distorting the geometry. The lack of delocalization of the π system is seen in the bond lengths of the hydrated and anhydrous structures, where there are distinct double and single bond lengths on either side of the bridging imine nitrogens.

The C-N single bonds range from ~1.40 and ~1.41 Å and the C-N double bonds are between ~1.29 and ~1.31 Å.171 The flexibility in the backbone and lack of delocalization of the π system is also seen in the dicarbahemiporphyrazine X-ray crystal structure (vide infra).

Figure 1.1.19: Crystal structures of anhydrous bis-pyridyl hemiporphyrazine (top) and monohydrate (bottom, side view left, top view right). Gray, light blue, white, and red spheres represent carbon, nitrogen, hydrogen, and oxygen respectively. Non-ionizable hydrogen atoms have been removed for clarity.171,172

Whereas most of the work on hemiporphyrazine systems has been on the bis- pyridyl variant, some work on dicarbahemiporphyrazine (dchp) have been reported. In

2001, Islyaikin et al. reported the first crystal structures of dicarbahemiporphyrazine

(Figure 1.1.21).173 They found that the macrocycle adopted a saddle shape conformation due to the hydrogen bonding between dimethylformamide and the isoindoline central nitrogen atoms of the macrocycle. Similar results were reported by Ziegler et al. when dicarbahemiporphyrazine was crystallized from various solvents (Figure 1.1.21). In all structures, there was a distinct difference between the Schiff base C-N bonds with length were approximately 1.40 Å and the shorter C=N bonds at ~1.27 Å. The bis-protonated

27 species was also isolated from a solution of formic acid. Interestingly, the bis-protonated dicationic adduct is planar, there is some electron delocalization between the meso nitrogens and the cyclic nitrogen of DII, and all ionizable hydrogen atoms reside at the meso nitrogen positions.174

Figure 1.1.20: Top (top left) and side view (top right) of free base dicarbahemiporphyrazine crystallized with dimethylsulfoxide and the dication of dicarbahemiporphyrazine (top view bottom left, side view bottom right). Gray, light blue, white, yellow, and red spheres represent carbon, nitrogen, hydrogen, sulfur, and oxygen respectively. Non-ionizable hydrogen atoms have been removed for clarity.174

Whereas most work has been done on the unsubstituted hemiporphyrazines, some work has been done on peripherally modified systems. The peripherally modified bis- pyridylhemiporphyrazine macrocycles are typically synthesized by reacting substituted

2,6-diaminopyridines and substituted DIIs or phthalonitriles.167,169,170,175–178 When 1,3- diiminoisoindolines with bulky substituent groups are used to synthesize hemiporphyrzines, a two-step reaction takes place where a trimer of two DII molecules linked by a diamino pyridine forms. The trimer then undergoes a template reaction with a divalent metal ion and a second equivalent of 2,6-diaminopyridine to close the macrocycle.170,179 Ziegler and coworkers presented the synthesis of a dihydroxy and tetrahydroxydicarbahemiporphyrazine in 2010 and trifluoromethyl substituted carbahemiporphyrazines in 2012 (Figure 1.1.22) through the reaction of catechol and resorcinol diamines with DII.180,181 In 2010, Muranaka and coworkers presented the synthesis of a tetrahydroxy dcph where 5,6-bis(2,6-dimethylphenyloxy)-1,3- diiminoisoindoline was used as the DII.182 In 2010, the first aliphatic hemiporphyrazine, cyclohexylcyanine, was presented. In cyclohexylcyanine, the benzene ring is replaced with a cyclohexane (Figure 1.1.22).183

Figure 1.1.21: Modified dicarbahemiporphyrazines.180,181,183

The localized electronic structures in the hemiporphyrazines result in broad absorbance transitions between 300-400 nm (for bis-pyridyl hemiporphyrazine, 1.1.23) and an absence of low energy transitions as is seen in phthalocyanines. This is the direct result of removing two opposing DII units and abrogating the aromaticity.184 In 2012, Muranaka and coworkers reported the first 18 π-electron aromatic dicarbahemiporphyrazine (Figure

1.1.24).182 Upon oxidation of the two resorcinol units by 2,3-dichloro-5,6- dicyanobenzoquinone (DDQ) to quinones, two new intense peaks appeared in the UV- visible spectrum (Figure 1.1.25) at 653 and 852 nm. In addition to a shift in the UV-visible spectrum, the chemical shift of the interior proton on the benzene ring moved upfield to

-0.49 ppm, indicating a diatropic ring current.

Scheme 1.1.9: Synthesis of 18 π-electron aromatic dicarbahemiporphyrazine (2) from dicarbahemiporphyrazine 1.182

The metalation chemistry of hemiporphyrazines has also been investigated.

Elvidge and Linstead proposed that upon metalation of bis-pyridyl hemiporphyrazine, the ionizable hydrogen atoms on the isoindoline units would be removed, resulting in a dianionic planar macrocycle. In 1952, they reported the metalation of bis-pyridyl hemiporphyrazine with Ni(II) and Pb(II), however, the nickel complex was not structurally characterized by single crystal X-ray diffraction until 1953 by Speakman.185,186 It was found that in the Ni(II) bis-pyridyl hemiporphyrazine structure was saddle shaped, not planar as Elvidge and Linstead had predicted (Figure 1.1.26). Several other research groups have published structures of Ni(II) bis-pyridyl hemiporphyrazine, all of which exhibit similar shapes in the macrocycles.172,187 Collamati et al. and Ziegler and coworkers reported the crystal structure of Ni(II) bis-pyridyl hemiporphyrazine upon exposure to pyridine. In these compounds, two pyridines coordinated to the axial position at the nickel

32 center, and the bis-pyridyl hemiporphyrazine was more planar than the previous unligated structures but maintained a ruffled geometry.188,189 In all structures, there was no indication of aromaticity in the C-N bonds in the backbone of the macrocycle. Additionally, in both the pyridine bound and planar adducts, the nickel center was bound asymmetrically to the macrocycle with the Ni-Npyridine bonds being slightly longer (~2.18 Å pyridine; ~1.98

171,186,188,190 Å free) than the Ni-Nindole bonds (~1.97 Å pyridine; ~1.90 Å free). The axial pyridine N-Ni bonds in the pyridine bound structure were significantly longer than the Ni-

N bonds to the macrocycle at ~2.20 Å.188,190

Figure 1.1.24: Ni(II) bis-pyridyl hemiporphyrazine. Top view (left) and side view (right). Gray, light blue, and green spheres represent carbon, nitrogen, and nickel respectively. Hydrogen atoms have been removed for clarity.186

Significant contributions to the metalation of bis-pyridyl hemiporphyrazine were made by Kenny and coworkers in the 1960s, who metallated the macrocycle with the elements sodium, potassium, tin, and germaium.175,191,192 Metalations of bis-pyridyl

33 hemiporphyrazine with transition metal ions (Co(II), Cu(II), Zn(II), Cd(II)) were reported by Smirnov in the late 1960s, along with some spectroscopy (UV-visible absorbance and

EPR for the Cu(II) adduct), decomposition, metal insertion kinetics, and purification.193–

197 Electrochemical investigations of the metal free bis-pyridyl hemiporphyrazine and metal complexes with Co(II), Ni(II), and Cu(II) were reported in 1972.198 Through the mid-

1970s to the early 2000s, more detailed studies of magnetic susceptibility, spectroscopy, and structure determinations were also published.171,172,188,199–206

The metalation chemistry of the dicarbahemiporphyrazines has been investigated, although not to the extent of the bis-pyridylhemiporphyrazine. The first reports of metallated dicarbahemiporphyrazines (dchp) came from the former Soviet Union in 1963.

After Borodkin and Gnedina’s initial report on the metalation of dchp with copper,

Smirnov later presented the metalation chemistry of Co(II), Ni(II), Cu(II), Zn(II), and

Cd(II).207 Through the 1960s to the early 2000s, there were multiple reports of on the synthesis of metallated dchp, their electronic spectra, conductivity, electrochemistry, spectroscopy, catalytic properties, metalation kinetics, solubility, and use as a polymer additive.195,207–226 Although there was a large amount of research on metalated dicarbahemiporphyrazines, structural characterization was lacking for these compounds.34

Ziegler and coworkers revisited the metalation of dchp with silver and copper in 2006.227

When dchp was reacted with AgNO3, the dchp coordinates the Ag(I) cation through the cyclic imine nitrogen of the DII (Figure 1.1.27). The presence of a nitrate anion in the crystal structure confirmed that the dchp was neutral when bound to the Ag(I) cation, and the authors proposed that the cyclic protons moved to the bridging nitrogen positions. The

Ag-Nimine bond lengths were 2.262(2) and 2.453(3) Å while the Ag-C distance was 2.709(3)

34 and 2.625(4) Å. In contrast, when reacted with copper salts, the expected copper (II) adduct did not form, but a copper (I) complex where a pyridine forms a C-N bond to the interior carbon position on one of the phenylene units (Figure 1.1.27). The Cu-Nimine bond lengths were 2.033(1) and 2.079(2) Å while the Cu-C(H) distance was 2.416(2) Å and the Cu-C(N) distance was ~2.74 Å. In both cases, the metal ions are coordinated at the axial position by a pyridine and reside above the plane of the macrocycle (~1.35 Å for the Ag(I) complex and ~0.77 Å for the Cu(I) complex), there is an agostic type interaction between the metal ion and the internal C-H, and the macrocycle maintains a saddle conformation.

Figure 1.1.25: Ag(I) dicarbahemiporphyrazine (left) and Cu(II) dicarbahemiporphyrazine (right). Gray, light blue, white, silver, and orange spheres represent carbon, nitrogen, hydrogen, silver and iron respectively. Non-ionizable hydrogen atoms have been removed for clarity. 227,228

The metal binding chemistry of unsubstituted dchp was also explored with cobalt, iron, zinc, manganese, lithium, nickel and palladium.181,189,228,229 The Co(II), Fe(II), and

Mn(II) complexes were synthesized by refluxing the appropriate metal carbonyl and dchp in pyridine under argon. In the Co(II) and Mn(II) complexes, the macrocycle was doubly

35 deprotonated to for charge balance. In the Fe(II) complex, the macrocycle ring is reduced at one of the α-isoindoline carbon positions and a neighboring meso nitrogen positions. 228

The neutral zinc complex was synthesized by reacting diethyl zinc with free base dchp in pyridine at room temperature under an argon atmosphere. The lithium adduct was formed through the reaction of lithium bis(trimethylsilyl)amide with free base dchp in tetrahydrofuran. Unlike the previous structures, the macrocycle in the lithium adduct is mono deprotonated with a single proton residing on one of the meso nitrogen atom positions. As was seen in the silver and copper complexes, the axial positions of the metal ions are coordinated by a pyridine, with the exception of the lithium adduct which is coordinated by a THF unless recrystallized from pyridine, and the complexes are saddle shaped.189

Unlike the other metal dicarbahemiporphyrazine complexes, when bis(1,5- cylcooctadiene)- nickel(0) was used as the metal source, the nickel activated the internal

C-H bonds of the benzene rings upon insertion. This results in a square planar coordination environment (Figure 1.1.28, top) around the Ni(II) center. The Ni-C bonds are 2.002(3)

190 and 2.004(3) Å while the Ni-Nindole bonds are 1.908(2) and 1.911(2) Å. The activation of internal C-H bonds was also reported by Muranaka and coworkers in 2014 when they inserted palladium into dchp (Figure 1.1.28, bottom).229 The Pd-C distances are 2.051 (4)

Å and the Pd-Nimine bond lengths are 2.012(3) Å. In both structures, the metal cation resides slightly above the plane of the macrocycle, with the Ni(II) center residing ~0.21 above the dchp plane.190 The distortion in the Pd(II) structure is effectively zero.229

Figure 1.1.26: Ni(II) dchp (top) and Pt(II) dchp (bottom). Gray, light blue, white, red, green and blue spheres represent carbon, nitrogen, hydrogen, and oxygen, nickel, and platinum respectively. Non-ionizable hydrogen atoms have been removed for clarity.190,229

Hemiporphyrazine is a non-aromatic analogue of phthalocyanine that has not been fully explored. Although they are easy to synthesize via Schiff base type condensations of

DII with diamines, the resultant products can suffer from poor solubility without peripheral modification.170 Although hemiporphyrazine has been known for over 50 years, a relatively small amount of work has been done in comparison to phthalocyanine, leaving it an open area of investigation.

1.2 Luminescence

Luminescence is the emission of light by a compound that is in an electronically excited state, allowing the compound to relax to lower energy state. Luminescence can typically be further divided into two subcategories, fluorescence and phosphorescence. The mechanism of both fluorescence and phosphorescence are described by the Jablonski diagram (Figure 1.2.1). Upon absorption of a photon an electron is promoted from the ground state (S0) to an excited state (S1, S2, etc.) as shown by the blue arrow in the figure.

The promoted electron can then undergo internal conversion, relaxing to a lower excited state such as S1. The electron then returns to the ground state through radiative decay

(orange arrow). This process does not involve a spin change, and thus is an allowed transition. They typical lifetime for an organic fluorophore is on the order of ~10-9 seconds.230

In phosphorescence, upon formation of the excited state and internal conversion, the electron undergoes a spin flip, a conversion from a singlet state to a triplet state, which is known as intersystem crossing. After internal conversion, the electron undergoes radiative relaxation, releasing light as it returns to the ground state (green arrow). In phosphorescence, the additional process of transitioning from the triplet state (T1) to the singlet ground state is symmetry forbidden, which results in longer lifetimes (~10-3-100 seconds).230

Figure 1.2.1: Simplified Jablonski Diagram.230

Fluorophores are selected for applications based on their lifetimes, quantum yields of emission, and Stokes shifts. The lifetime (τ) is the average time between excitation of a molecule and the return to the ground state.230 The lifetime of a molecule can be calculated from Equation 1.2.1, where τ is the lifetime, Γ is the radiative decay rate to S0, and knr is the non-radiative decay rate to S0.

1 τ = Equation 1.2.1 Γ+푘푛푟

The quantum yield of emission is the ratio of photons absorbed to photons emitted and can be calculated by Equation 1.2.2,

2 퐺푟푎푑푥 휂 푥 ∅푥 = ∅푆푇 ( ) ( 2 ) Equation 1.2.2 퐺푟푎푑푆푇 휂 푆푇 where ∅ is the quantum yield of emission of the standard (ST) and the Grad is the gradient from the plot of integrated fluorescence intensity vs absorbance of the standard (ST) and the analyte (x) The quantity 휂 is the refractive index of the solvent used.231 The Stokes shift is defined as the difference in the wavelength of maximum absorbance (λmax) and

232 wavelength of emission (λem).

Organic fluorophores have found broad utility in biological applications, forensics materials, as sensors, and as imaging molecules since thier discovery in the late

1800s.230,232,233 In the biological sciences, organic fluorophores can be appended to a targeting moieties for cellular imaging.230,233 Some of the most important classes of fluorophores (Figure 1.2.2) include the xanthene dyes (rhodamine and fluorescein),232–239

232,235,236,239–242 35,232,239,242 coumarin dyes, porphyrinoids, mono BF2 containing dyes such as

BODIPY (BOron-DIPYrromethene),232,235,238,239,242–247 aza-BODIPY (aza- BOron chelated

238,239,243,244,248,249 -DIPYrromethene), and more recently, bis BF2 dyes such as BOPHY

250–253 (bis(difluoroboron)1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine). The BF2 containing dyes will be discussed later in this chapter.

Figure 1.2.2: Structures of common fluorophores.

Fluorescein and rhodamine compounds absorb in the green region (~500 nm) of the visible light spectrum, have high extinction coefficients, and exhibit large quantum yields of emission. These characteristics render them ideal for biological applications.254

Fluorescein is a pH sensitive fluorophore that can ionize (+1 to -2, Figure 1.2.3), becoming more fluorescent in basic conditions as it deprotonates. 232,254,255 Although fluorescein has found broad use in applications and its electronic properties can be tuned by changing the substitution on the periphery, this fluorophore also has the disadvantages of photobleaching, broad emission that limits its use in multi-color arrays, and self-quenching in some chemical environments.254 Like fluorescein, rhodamine can be cationic in acidic media or exist in equilibrium between the zwitterionic and lactone conformations with the absorbance and emission properties being directly dependent on its protonation state.256

Figure 1.2.3: Protonation states of fluorescein.255 Coumarin is a naturally occurring highly fluorescent dye that was first isolated from the tonka bean (Dipteryx odorata).254,257 The prototypical coumarin, 4-methyl-7- hydroxycoumarin (Figure 1.2.4), absorbs in the UV at 360 nm (ε = 1.7 x104M-1cm-1) and emits blue light at 450 nm with a quantum yield of ~ 60%. The pKa of 4-methyl-7- hydroxycoumarin is 7.8, making it sensitive to changes in pH under physiological conditions; however, halogenating this compound reduces the pKa, making it less sensitive.235 In addition to being of interest for its fluorescent properties, coumarin derivatives can be used in pharmacological applications.257

Figure 1.2.4: 4-methyl-7-hydroxycoumarin.235

Cyanine dyes are cationic fluorophores that were first synthesized in 1856.235,258 It was not until after 1993 that the cyanine dyes were used for applications other than staining cell membranes and DNA.235 Cyanine dyes have large extinction coefficients, high quantum yields of emission, and narrow emission profiles.258 In addition to controlling the electronic properties through substitution at the periphery of the molecule, increasing the length of the polymethene chain causes a red shift in absorbance.235

Phthalocyanine dyes absorb at wavelengths <600 nm (λmax = 665 for ZnPc, emission

43 232 at 670 nm, φ = 0.321 in CHCl3) and into the IR region. The spectra can be further red shifted by expanding the π system.259 While Pcs are photostable, the Stokes shift can be relatively small in these compounds.43,232 With the absorbance and emission spectra of being in the red to near IR region of the spectrum, Pcs are good candidates for biological imaging and photosensitizers for photodynamic therapy.232,260,261 Pcs have been encapsulated in nanoparticles, micelles, liposomes, surfactants, and modified to be water soluble and used for detection of DNA, bioimaging of tumors, and photodynamic therapy.262–268 In addition to having desirable absorbance properties, phthalocyanines are non-toxic (when used for imaging) and have a low to no dark toxicity (when used for photodynamic therapy).35,267,268

BF2 fluorophores: BODIPY Dyes

Since its synthesis in 1968 by Treibs and Kreuzer, 4,4-difluoro-4-bora-3a,4a-diaza- s-indacene (BODIPY, Figure 1.2.5) had been modified for use as chemical sensors, biological imaging agents, dyes, OLEDs, and energy harvesting molecules.243,269

Figure 1.2.5: BODIPY core with numbering (left) and crystal structure of unsubstituted BODIPY (right). Gray, light blue, pink and green atoms represent carbon, nitrogen, boron, and fluorine respectively. Hydrogen atoms have been removed for clarity.270

While BODIPYs has been known since their initial synthesis in the 1960s, unsubstituted

BODIPY (Figure 1.2.5) was not synthesized until 2009.270–272 BODIPY can be classified as a rigid monomethine cyanine (1.2.6), where the boron center chelated by the two nitrogen atoms of the pyrrole rings, forming a highly conjugated, rigid, planar backbone.273

In addition to being a rigified cyanine, the BODIPY structure is structurally similar to s- indicine (1.2.6), where two cyclopentadiene rings are linked by a benzene ring.273 In unsubstituted BODIPY, the B-N bond is 1.5450(14) Å and the B-F bonds measure

1.3875(12) Å and 1.3958(13) Å. The backbone of the complex is nearly planar, with the boron deviating out of the plane of the pyrroles by only ~ 4.3°.271

BODIPY is an ideal molecule for fluorescence applications due to its strong UV- visible absorbance, high quantum yields of emission, photostability, ease of synthesis, and ready modification. Recent research has focused on bathochromically shifting the maximum absorbance and emission wavelengths as well as increasing the Stokes shift.243,274 BODIPYs are typically synthesized via the condensation of two pyrrole units with either acyl chlorides or aldehydes followed by oxidation and complexation with

BF3•OEt2 (Scheme 1.2.1).

Figure 1.2.6: Cyanine (left), rigified cyanine (middle left), s-indicine (middle right) and BODIPY core (left).273

Scheme 1.2.1: Synthesis of symmetric BODIPY from pyrroles and an aldehyde.243

These methods are commonly used for the synthesis of symmetric BODIPYs; however, for an asymmetrically substituted product, a ketopyrrole intermediate can first be formed, followed by a Lewis acid mediated condensation with another equivalent of pyrrole

(Scheme 1.2.2).243,245,275 The BODIPY core is robust and can tolerate modification after the BF2 adduct has been formed. One of the most common modifications of BODIPY is

45 halogenation, which can be followed by palladium cross coupling reactions. In addition to halogenation, when methyl groups are present at the 3 and 5 positions, BODIPYs can be condensed with aldehydes in Knoevenagel reactions to form C=C bonds.243,245,274

Scheme 1.2.2: Synthesis of BODIPY from ketopyrroles.243

The BODIPY pyrrole ring can be easily halogenated at each position (Scheme

1.2.3) by using Cl2, Br2, N-bromosuccinimide (NBS), N-chlorosuccinimide (NCS), or

I2/HIO3. The most reliable procedure for halogenation at the 3 and 5 positions is treatment of dipyrromethane with either NBS or NCS at -78°C followed by the addition of

276 BF3•OEt2. To halogenate at the 2 and 6 positions, BODIPY can be reacted with Cl2, Br2,

276 I2, or the appropriate N-halosuccinimide (NXS) at room temperature. Unlike substitution at the 3,5 or 2,6 positions, halogenation at the 1,7 positions can only take place when all other pyrrolic carbon positions are substituted.277 Treatment of an appropriate pyrrole with

NXS or 1,2,5,6 substituted BODPY with Br2 yields the 1,7-halogenated species. After halogenation of the BODIPY core, further modification can be carried out with palladium catalyzed cross coupling reactions such as Stille, Suzuki, Heck, and Sonogashira methods

(Figure 1.2.7).243,245,274,278,279

Scheme 1.2.3: Halogenation of BODIPY core.278

Figure 1.2.7: Palladium cross coupling reactions of BODIPY.280

Substitution at each of the eight positions has a different effect on the electronic properties of BODIPY (Figure 1.2.8), allowing them to be tuned for particular applications.

When substituted at the 3 and 5 positions, BODIPY absorption and emission maximum tends to have larger red shifts than those with substituents at the 1 and 7 positions. When substituted at the 2 and 6 positons, a larger stokes shift is generally observed versus with other substitution patterns. Substitution at the 8 position has little effect on the absorption and emission spectrum in comparison to substitution on the pyrrole carbons.245,274

Figure 1.2.8: Absorption and emission data for various BODIPY substitution patterns.243,270,274,281 Aza-BODIPY

Aza-BODIPY (Figure 1.2.9) is a BODIPY analog where the meso carbon is replaced with nitrogen. The aza-dipyrromethene ligand was first reported well before the synthesis of BODIPY in the 1940s by Rogers, who reported the appearance of an intensely dark blue product upon heating nitrobutyrophenone in the presence of ammonium formamate and formamide.282–284 The aza-dipyrromethene (ADPM) ligand was first reacted with boron in

1993 by Boyer and coworkers.285

Figure 1.2.9: Aza-BODIPY core.

In the early 2000s, O’Shea and coworkers reported the synthesis of aza-BODIPYs and investigated their use as a photodynamic therapy agent in cell studies (Figure 1.2.10).

They demonstrated that both the brominated and non-brominated compounds could produce singlet oxygen upon irradiation, with aza-BODIPY 4 being more efficient than 2b.

When a non-brominated aza-BODIPY was dissolved in a water–cremophor solution and incubated with HeLa cells, it was shown that the complex accumulated in the cytoplasm.248

Figure 1.2.10: First aza-BODIPYS tested as PDT agents.248

O’Shea’s 2002 report included the crystal structure of complex 2b (Figure 1.2.11).

The B-N bond lengths were 1.563(7) and 1.562(5) Å while the B-F bond lengths were

1.365(6) and 1.376(6) Å. In the structure, the pyrrole backbone is approximately planar with the boron deviating out of the plane of the pyrroles by ~ 4.5ᵒ.248 This is consistent with the binding motif that is seen in BODIPY structures. As with BODIPY complexes, aza-

BODIPYs have high extinction coefficients, narrow absorbance and emission bands, high quantum yields of emission, and good photostablities.244,286 O’Shea’s 2002 report included the crystal structure of complex 2b (Figure 1.2.11). The B-N bond lengths were 1.563(7) and 1.562(5) Å while the B-F bond lengths were 1.365(6) and 1.376(6) Å. In the structure, the pyrrole backbone is approximately planar with the boron deviating out of the plane of the pyrroles by only ~ 4.5ᵒ.248 This is consistent with the binding motif that is seen in

BODIPY structures. As with BODIPY complexes, aza-BODIPYs have high extinction coefficients, narrow absorbance and emission bands, high quantum yields of emission, and good photostablities.244,286

Figure 1.2.11: Crystal structure of aza-BODIPY 2b. Gray, light blue, pink, green, and red spheres represent carbon, nitrogen, boron, fluorine, and oxygen respectively. Hydrogen atoms have been removed for clarity.248

In 2016, Karlsson and Harriman investigated the photophysical differences between

BODIPY and aza-BODIPY experimentally and through calculations by investigating

BODIPY A and aza-BODIPY B (Figure 1.2.12). It was shown experimentally that the absorbance and emission spectra of aza-BODIPY B is red-shifted in comparison to

BODIPY A. The calculations showed that the bathochromic shift in aza-BODIPY arises from the meso nitrogen atom, which reduces the HOMO-LUMO gap to 1.86 eV, in contrast to a gap of 2.27 eV in BODIPY.287

Figure 1.2.12: Absorbance (black line) and emission spectra (gray line) for BODIPY A and aza-BODIPY B.287 (Figure reprinted with permission from J. Phys. Chem. A. 2016, 120 (16), 2537–2546. Copyright © 2012 American Chemical Society)

Today, there are two common methods for ADPM synthesis. In the first route, 2,4- diarylpyrroles are converted into their 5-nitroso derivatives, then condensed with a second equivalent of pyrrole (Scheme 1.2.4).243 The second method, presented by O’Shea and coworkers, consists of a Michael addition of nitromethane to diaryl α,β-unsaturated

52 ketones, also known as chalcones, in the presence of the base diethylamine (DEA) to afford

1,3-diaryl-4-nitrobutan-1-one compounds. The nitroketone is then refluxed in alcololic solvents in the presence of an excess of ammonium acetate to form aza-dipyrromethene in good yields (Scheme 1.2.5).249 Chalcones can be obtained from commercial sources or easily synthesized from the condensation of aldehydes and ketones in the presence of sodium hydroxide in ethanol.249,288 After the synthesis of the free ligand, it is reacted with

243,248,274,285 BF3•OEt2 in the presence of a base to afford aza-BODIPY.

Scheme 1.2.4: Synthesis of ADPM from 5-nitroso pyrrole.243

Scheme 1.2.5: Synthesis of ADPM from chalcones.249

BF2 complexes of 3,3’-diaryldiisoindolylmethene

In 1972, Bredereck and Vollman presented the synthesis of π-extended 3,3’- diaryldiisoindolylmethenes through the reaction of phthalonitrile with aryl Grignard reagents (Scheme 1.2.6, top). Although they were unable to isolate the alkali complexes of

3,3’-diaryldiisoindolylmethene, they were able to isolate the copper complex (Scheme

1.2.6, bottom).289

Scheme 1.2.6: Synthesis of 3,3’-diaryldiisoindolylmethene (top) and the Cu(II) complex of 3,3’-diaryldiisoindolylmethene. 289 As an extension of their work on phthalocyanines, Kobayashi and coworkers revisited the synthesis of π-extended 3,3’-diaryldiisoindolylmethenes that were reported by Bredereck and Vollman.289 After the ligand was synthesized, it was reacted with

BF3•OEt2 in the presence of DIPEA (Scheme 1.2.7). The resultant difluoroboron complexes had significantly red shifted absorbance bands (~720 nm). The compounds were also fluorescent, emitting light around 740 nm with quantum yields of ~13%.

Scheme 1.2.7: Synthesis of difluoroboryl complexes of 3,3’-diaryldiisoindolylmethene.290

Crystals of the difluoroboryl complex of 3,3’-diaryldiisoindolylmethene (R=H) were analyzed by single crystal X-ray diffraction. In the difluoroboryl complex of 3,3’- diaryldiisoindolylmethene (R=H), it was found that the boron center had a tetrahedral geometry, where the two isoindole moieties maintained a planar conformation with B-N bond lengths of 1.573(2) and 1.579(2) Å and B-F bond distances of 1.372(2) and 1.380(2)

Å.(ref) The bond distances and coordination geometry of the boron center are consistent with what is seen in analogous aza-BODIPY compounds.290

Aza-(dibenzo)dipyrromethene

While Cammidge and coworkers were working on synthesizing a class of phthalocyanine/ porphyrin hybrids, the tetrabenzotriazaporphyrins (TBTAB), they noticed that in addition to the desired cyclotetramerization product, there was a significant amount of side product from the self-condensation of the starting material (Scheme 1.2.8).291 The synthesis was later modified to reflux an aminoalkeneisoindoline in toluene to obtain the aza-dibenzodipyrromethene (ADBM) in high yields (<80%). The resultant ADBM was then reacted with BF3•OEt2 in the presence of base to afford aza-(dibenzo)BODIPY.

Scheme 1.2.8: First synthesis of aza-(dibenzo)dipyrromethene.291

The aza-(dibenzo)BODIPY adduct had a maximum absorbance at 469 nm, and emission at 560 nm with a quantum yield of <1%. Although the boron adducts were expected to have a larger quantum yield of emission, it was surmised that one mechanism of non- radiative decay was possible E/Z photoisomerization. As is seen with BODIPY and aza-

BODIPY compounds when analyzed by single crystal X-ray diffraction, the boron center has a tetrahedral geometry (Figure 1.2.13) with B-N bond lengths of 1.528(6) and 1.537(4)

Å and B-F bond lengths of 1.398(5) and 1.402(6) Å.

Figure 1.2.13: Crystal structure of the BF2 complex of aza-(dibenzo)dipyrromethene. Gray, light blue, pink, green, and red spheres represent carbon, nitrogen, boron, fluorine, and oxygen respectively. Hydrogen atoms have been removed for clarity.292

Bis Boron fluorophores

293–295 In addition to bis BODIPY dyes , several examples of bis boron dyes (Figure

1.2.14) can be found in the literature. Inspired by the ability of 1,8-naphthyridine to hydrogen bond to DNA, Fu and coworkers synthesized bis BF2 1,2-bis(5,7-dimethyl-1,8- naphthyridin-2-yl)hydrazine, which is fluorescent in both the solid state and in solution.

The bis BF2 compound had a high quantum yield of emission (0.965) in dichloromethane, however, in dimethylsulfoxide, the quantum yield was significantly lower (0.767).296 Hicks et al. transformed indigo into a diketimine and complexed the ligand with BF2. Although the bis BF2 complex was not stable in solution and decomposed to the mono BF2 complex over a few days, its absorbance and emission spectra were significantly redshifted (λmax =

297 ~740 nm/ λem = ~800 nm) with a weak emission. Umland and later Gudipati reported

298,299 the bis BF2 2,2’-pyridil and bis B(OEt)2 2,2’-pyridil respectively. Although first reported by Umland in 1973, the photophysical properties of BF2 2,2’-pyridil were not reported until 2014 by Xiao and coworkers (λmax = 410 nm/ λem = 486 nm/ Φ= 0.63 in

300 dichloromethane). Gomes and coworkers synthesized the bis BPh2 2-(N- aryl)formiminopyrrole complex. When fabricated into light emitting devices, the emission wavelength red shifted by ~20 nm.301 Based on the scaffold of pyrimidine, Kubota et al. synthesized a bis BF2 pyridimine β-iminoenolate complex. The resultant complex was fluorescent and the emission spectra were red shifted in more polar solvents.302 Ladder- type (fully ring fused) BPh2 complexes have also shown promising photophysical properties for incorporation into organic light emitting devices.303–306

Figure 1.2.14: Structures, absorbance, and emission data of some bis BF2 fluorophores.

BF2 has also been coordinated to the salphen family of compounds. In 2001,

Kunkely and Volger explored the optical properties of a bimetallic boron salen complex

(Figure 1.2.15) that was previously synthesized by Wei and Atwood.307,308 The bis

B(OMe)2 salen complex had a broad absorbance at 348 nm with an extinction coefficient of 5,400 M-1cm-1. When irradiated at 350 nm, the compound fluoresced with emission at

460 nm and a quantum yield of 0.51 in acetonitrile.308 In 2007, Jiang and coworkers incorporated two BF2 units into N,N’-o-phenylenebis(salicylideneimine) and N,N’-p- phenylenebis(salicylideneimine) (Figure 1.2.15) and evaluated their efficiency when incorporated into light emitting devices. Although the fabricated devices were functional, the efficiency was on par with current devices.309 More recently, Lu et al. found that when substituted at the 6 and 8 positions with t-butyl groups, the BF2 complexes of N,N’-o- phenylenebis(salicylideneimine) and N,N’-m-phenylenebis(salicylideneimine) exhibited reversible piezofluorochromism.310

Figure 1.2.15: Bimetallic boron complexes of salen (left) and N,N’-p- phenylenebis(salicylideneimine).308,309

BOPHY

Ziegler and coworkers presented the synthesis of a novel bis BF2 pyrrole based fluorophore, bis(difluoroboron)1,2-bis((pyrrol-2-yl)methylene)hydrazine (BOPHY) in

2014. The bis pyrrole azine scaffold was first reported in the early 1980s followed by subsequent reports coordinating it to various transition metal, lanthanide, and actinide

59 ions.311–321 The ligand was synthesized by condensing two equivalents of pyrrole carboxaldehyde with hydrazine in the present of an acid catalyst to afford the bis pyrrole

Schiff base product, which was then reacted with BF3•OEt2 (Scheme 1.2.9). The resultant product had quantum yields near unity (vide infra) and was photostable to air, light, and

UV irradiation for long periods of time.

250,253 Scheme 1.2.9: Synthesis of unsubstituted and Me4BOPHY.

Like BODIPY, the pyrrole BF2 backbone of BOPHY is planar six membered ring with the exception of the fluorine atoms (Figure 1.2.16). The unsubstituted BOPHY absorbs at 424 nm and 444 nm with extinction coefficients of 4.09 × 104 and 3.86 × 104

M−1 cm−1 respectively. When irradiated at 424 nm, unsubstituted BOPHY emits at 465 and

493 nm with a quantum yield of 95%. The tertamethyl BOPHY (Me4BOPHY) has a red shifted absorbance and emission profile in comparison to the unsubstituted variant, with

4 4 −1 λmax at 444 nm and 467 nm with extinction coefficients of 3.75 × 10 and 3.74 × 10 M cm−1, emission at 485 and 518 nm when irradiated at 444 nm with a quantum yield of 92%.

Figure 1.2.16: Crystal structure of Me4BOPHY. Gray, light blue, pink, and green spheres represent carbon, nitrogen, boron, and fluorine respectively. Hydrogen atoms have been removed for clarity.250

Shortly after the first report of BOPHY, Hao et al. published a series of modified

BOPHY adducts (Figure 1.2.17). They first condensed the appropriate pyrrole carboxaldehyde with hydrazine in the presence of acetic acid, followed by reaction with

BF3•OEt2 to afford the BF2 complexes. All synthesized adducts were red shifted in absorbance and emission in comparison to unsubstituted BOPHY. BOPHY 1c and 1d had high quantum yields of emission (100% in dichloromethane for 1c and 1d), however,

BOPHY 1e was significantly less at 6% in dichloromethane.253

Figure 1.2.17: Modified BOPHY adducts and their absorbance and emission data in dichloromethane.253

The pyrrole backbone of BOPHY can be easily modified using the methodologies established for BODIPY, modifying its electronic properties. The first reported post synthetic modification of BOPHY was also presented in Hao’s 2014 manuscript. In this report, they presented the Knoevenagel condensation of Me4BOPHY with 4-N,N- dimethylbenzadeldehyde (Scheme 1.2.10), and the resultant product had a red shifted absorbance and emission in comparison to unsubstituted BODIPY with λmax=557 nm (ε=

4 −1 −1 253 6.3x10 M cm ) and λem=667 nm (Q.Y.= 20%) in dichloromethane.

Scheme 1.2.10: Knovenagel condensation of Me4BOPHY with 4-N,N- dimethylbenzadeldehyde to form 4-N,N-dimethylbenzyl monostyryl-BOPHY .253

In the UV-vis spectra, the maximum absorbance undergoes a small hypsochromic shift when taken in polar solvents vs nonpolar solvents. The emission spectra and quantum yield measurements show strong polarity dependence. In nonpolar solvents, the emission is at 581 nm with a quantum yield of 45% (hexane); in polar solvents, the emission is red shifted to 721 nm and a quantum yield of 1% (acetonitrile) as shown in Figure 1.2.18. In addition to being solvent dependent, the absorbance and emission profile are pH dependent.

This effect of pH on 4-N,N-dimethylbenzyl monostyryl-BOPHY was further investigated by Jiang and coworkers.322 They found that in basic conditions, the complex was non- emissive, however, when titrated with HCl and subsequent protonation of the distal nitrogen, the absorbance shifted from a bimodal peak at 536 and 557 nm to a single broad peak at 504 nm. In addition, there was an increase in quantum yield from 0.1% to 98% in acidic conditions (Figure 1.2.18).

Figure 1.2.18: Normalized UV-vis (top left) and emission spectra (top right) of 4-N,N- dimethylbenzyl monostyryl-BOPHY in solvents of varying polarity and the absorbance spectra (bottom left) and emission spectra (bottom right) after the addition of HCl. 253,322 (Figures reprinted with permission from Org. Lett. 2014, 16 (11), 3048–3051. Copyright © 2014 American Chemical Society. RSC. Adv. 2015, 5, 16735–16739. Copyright © 2015 Royal Society of Chemistry)

In addition to a monostyryl BOPHY, there are a few reports of distyryl BOPHY adducts that were synthesized through double Knoevenagel reactions. Ziessel et al. reported the synthesis of a broadly absorbing thienyl appended BOPHY for the use in bulk heterojunction solar cell applications (Figure 1.2.19, left).323 Ziegler and coworkers reported first organometallic appended BOPHY which was synthesized through the double

Knoevenagel reaction of ferrocene carboxaldehyde with Me4BOPHY(Figure 1.2.18,

64 right).252 Unlike the previously reported BOPHY complexes, the bis-ferrocene BOPHY did not fluoresce in solution due to quenching by the ferrocene moiety.

Figure 1.2.18: Thienyl appended BOPHY (left) and bis-ferrocene BOPHY (right).252,323

Ziessel also reported the first post synthetic halogenation and palladium cross coupling reactions of BOPHY to tune the electronic properties.324 After halogenation of

Me4BOPDHY with ICl, followed by a Sonogashira coupling with 3- peryleneacetylene

(Scheme 1.2.11), the resultant complex was significantly redshifted with a λmax = 590 nm

(ε = 65,700 M-1cm-1) and a smaller absorbance at 430 nm from the BOPHY and perylene portions of the complex. When the perylene moiety was irradiated with light, there was a small emission band at 515 nm (perylene emission) and a large emission band at 631 nm

65 from BOPHY, showing an almost quantitative energy transfer from the perylene to

BOPHY.324 Using the same methods as Ziessel, Son et al. reported a series of mono and bis BOPHY derivatives that were modified at the 4 and 4’ postions that were fluorescent in solution an in the solid state (Scheme 1.2.12, Table 1.2.1) with good quantum yields of emission.325

Scheme 1.2.11: Synthesis of bis-styryl 4-ethynylperylene BOPHY.324

Scheme 1.2.12: Synthesis of mono and bis ethynyl BOPHYs 1a-c and 2a-c. 325

Table 1.2.1: Absorbance and emission data for 1a-c and 2a-c in dioxane.325

Compound λmax λem solution Φ solution λmax solid λem solid λem film solution (nm) (nm) (nm) (nm) (nm) (nm) / ε (x104 M- 1Cm-1) 1a 453/ 3.23 499 0.83 458 554 507 475/ 3.23 530 482 536 1b 456/ 5.49 509 0.70 462 567 520 477/ 5.49 836 485 544 1c 459/6.76 523 0.35 465 572 540 479/ 7.08 486 2a 464/ 6.31 512 0.73 469 561 520 484/ 6.71 544 494 542-550 2b 470/ 4.68 524 0.72 476 591 536 469/ 4.68 498 2c 468-495/ 536 0.46 483-503 599 547 2.63

Halogenated BOPHYs have also been investigated for use in triplet–triplet annihilation upconversion and singlet oxygen generation. Zhang and Zhao investigated the triplet–triplet annihilation upconversion and singlet oxygen producing abilities of a series of iodated monostyryl-BOPHYs (Figure 1.2.19).326 These BOPHYs were modified using a Knoevenagel reaction to extend the π-conjugation and tune the electronic properties. The addition of iodine at the 4 and 4’ positions enhanced intersystem crossing (ISC). When excited at 473 nm with no 9,10-diphenylanthracene (DPA) present, C-2 emitted at 502 nm.

When DPA was present, the emission was upconverted to 390-475 mn with a quantum

1 yield of 2.8%. All compounds were also examined for their singled oxygen ( O2)

1 generation (Table 1.2.2). It was found that most compounds had a significantly lower O2

1 quantum yield than BODIPY 4, with the exception of C-2 which had a O2 φ = 0.58.

Figure 1.2.19: BOPHY complexes tested for triplet–triplet annihilation upconversion and singlet oxygen production.326

Table 1.2.2: Quantum yields of singled oxygen generation for several BOPHY compounds.326

1 Compound O2 φ

C-2 0.58

C-3 0.35

C-4 0.43

C-5 0.41

C-6 0.49

BODIPY 4 0.85

Jiang and coworkers reported the synthesis and use of a brominated tetraphenyl BOPHY for its ability to produce singlet oxygen. The tetraphenyl BOPHY has a λmax = 508 nm (ε =

60,000 M-1cm-1) and emitted at 524 nm (Φ = 0.96). When the 4,4’ bromo tetraphenyl

BOPHY was in solution with the singlet oxygen scavenger 1,3-diphenylisobenzofuran

(DPBF) at concentrations of 5 x 10-6 M and 6 x 10-5M respectively, it was found that after irradiation at 500 nm for 6 minutes, 80% of the DPBF had been oxidized with complete oxidation after 26 minutes. In addition, there was no photobleaching of 4,4’ bromo tetraphenyl BOPHY.327

In addition to changing the periphery of the pyrrole rings, exchanging the fluorine atoms for phenyl rings changes the absorbance and emission profile. In 2016, Shen and Lu reported the reaction of the pyrrole diimine precursors with triphenylborane. In addition to the expected six membered ring in the backbone, the observed the formation of a five membered ring in the backbone of the tetramethyl adduct (Figure 1.2.20) which was not

253,328 seen in previous BF2 BOPHY systems. The unsubstituted BPh2 BOPHY has a slightly red shifted absorbance at 438 nm. In contrast, the BPh2 Me4BOPHY absorbed at 486 and

521 nm, a red shift of 42 nm in comparison to Me4BOPHY. Both compounds were emissive with quantum yields of 69% (unsubstituted BPh2 BOPHY) and 57% in dichloromethane

(BPh2 Me4BOPHY).

Figure 1.2.20: Crystal structures of BPh2BOPHY (left) and BPh2 Me4BOPHY (right). Gray, light blue, and pink sphers represent carbon, nitrogen, and boron respectively. Hydrogen atoms have been removed for clarity.328

BOPHY is a highly fluorescent, photostable molecule with quantum yields near unity in some cases. The periphery can be easily modified to tune the electronic properties by extending the π system as well as adding heavy atoms for use as a singlet oxygen generator and upconversion of light to higher energies. In addition to modification of the pyrrole rings, the substitution on the boron center can be changed, leading to a shift in the overall shape of the complex and a change in the absorbance and emission spectra.

Chapter II

RE(CO)3 TEMPLATED FORMATION OF AZA(DIBENZO)DIPYRROMETHENES

The text of this chapter is a reprint of the material as it appears in: Crandall, L.A.;

Bogdanowicz, C.A.; Hasheminasab, A.; Chanawanno, K.; Herrick, R.S.; Ziegler, C.J.

DOI: 10.1021/acs.inorgchem.5b02934

Introduction

The phthalocyanines are most typically synthesized via templating reactions, using metal ions to condense four equivalents of a precursor molecule. Phthalocyanine precursors include a variety of ortho substituted benzenes, such as phthalonitrile, or ortho cyanobenamide or bicyclics compounds such as phthalimide, and 1,3-diiminoisoindoline

(compound 1, Figure 2.1). For most metal ions, these templating reactions result in the formation of normal phthalocyanines.18,329–331 However there are two well-known reactions where large (the uranyl cation) and small (boron halide) templating agents produce expanded (superphthalocyanine) and contracted (subphthalocyanine) analogs,

71 respectively.85,91,92,94 In both cases, the radius of boron or uranium controls the type of macrocycle that forms.

Outside of this chemistry, there are few examples of alternate macrocycles or chelates being formed; a report by Siegl presented templating reactions proceeding by metal-based condensation of phthalonitriles and 2,6-diaminopyridines to afford metalated hemiporphyrazines and isoindoline based chelates.169 Outside of these few examples, the template synthesis of phthalocyanine analogues and phthalocyanine-like chelates remains largely unexplored.

In another area of investigation, there has been recent interest in the synthesis of aza(dibenzo)dipyrromethenes (ADBMs, Figure 2.1), which can be considered as a half of a phthalocyanine macrocycle.290 Much of the recent interest in this molecule is driven by work on the compounds BODIPY and aza-BODIPY (Figure 2.1), which have been extensively investigated as fluorescent chromophores.238,274,290 However, in spite of this interest, there has been little progress in the synthesis of ADBMs. Several years ago,

Lukyanets and Kobayashi presented the synthesis of aryl substituted ADBMs using

Grignard reagents and phthalonitrile,290 based on work by Bredereck and Vollmann.289

Since then, there has been several reports on the chemistry of aryl substituted ABDMs.332–

336 More recently, Cammidge and co-workers have synthesized an alkene terminated

ADBM via the condensation of two alkeneiminoisoindolines.292 Additionally, in 2015 Li and co-workers presented the synthesis of asymmetric isoindoline based chelates using phthalonitrile as the starting material.337 Based on this work, we surmised that a aza(dibenzo)dipyrromethene might also be produced from simple isoindoline starting

72 materials using a templating agent. In particular, we thought that we could avoid phthalocyanine or macrocycle formation by the use of metal ion templates that could prevent ring formation.

Figure 2.1. Templated synthesis of aza(dibenzo)dipyrro-methenes.

We have been investigating the fundamental chemistry of compounds that contain the Re(CO)3 unit, many of which can be readily synthesized from commercially available

+ 338–340 Re(CO)5X starting materials or via the Re(CO)3(H2O)3 ion. The Re(CO)3 unit has the potential to be a unique templating agent for two reasons: first, the carbonyl units are effectively non-labile in the presence of ligands that lack significant back bonding, and second, the three carbonyls retain a rigid facial geometry. Ligands such as nitrogenous bases exclusively adopt facial coordination modes when bound to the Re(CO)3 unit; we hypothesized that this characteristic might be useful for templating alternate geometries

73 from diiminisoindoline or other phthalocyanine precursor compounds, particularly because the standard square planar geometry adopted by many transition metal ions could not occur with the Re(CO)3 unit. In this report, we present the synthesis of bis(oxo) and bis(imino) terminated ADBMs using the Re(CO)3 moiety to condense two equivalents of the phthalocyanine precursor diiminoisoindoline (Figure 2.1).

Experimental

General Information

All reagents were purchased from TCI Chemical, Acros Organics or Sigma-

Aldrich and used as received. 1,3-Diiminoisoindoline (DII, 1) was prepared according to

Elvidge’s modified procedure.164 Column chromatography was performed on alumina

(Dynamic Adsorbents, Inc, 63-200 μm). Deuterated solvents were purchased from

Cambridge Isotope Laboratories and used as received.

NMR spectra were recorded on 300, 400 and 500 MHz Varian spectrometers.

Chemical shifts were given in ppm relative to residual solvent resonances (1H, 13C NMR spectra). High resolution mass spectrometry experiments were performed on a Micromass

ESI-Tof™ II (Micromass, Wythenshawe, UK) mass spectrometer equipped with an orthogonal electrospray source (Z-spray) operated in positive ion mode. Sodium iodide was used for mass calibration for a calibration range of m/z 100-2000. Samples were prepared in a solution containing acidified methanol and infused into the electrospray source at a rate of 5-10 μL min-1. Optimal ESI conditions were: capillary voltage 3000 V, source temperature 110oC and a cone voltage of 55 V. The ESI gas was nitrogen. Data was acquired in continuum mode until acceptable averaged data was obtained.

X-ray intensity data were measured on a Bruker CCD-based diffractometer with dual Cu/Mo ImuS microfocus optics (Cu Kα radiation, λ = 1.54178 Å, Mo Kα radiation, λ

=0.71073 Å). Crystals were mounted on a cryoloop using Paratone oil and placed under a steam of nitrogen at 100 K (Oxford Cryosystems). The detector was placed at a distance of

4.00 cm from the crystal. The data were corrected for absorption with the SADABS program. The structures were refined using the Bruker SHELXTL Software Package

(Version 6.1), and were solved using direct methods until the final anisotropic full-matrix, least squares refinement of F2 converged. UV-Vis spectra were recorded on a Hitachi UV-

Vis spectrophotometer (U-3010).

Synthesis of 2.2-2.7:Synthesis of 2.2: Re(CO)5Cl (40.4 mg, 0.111 mmol) and a solution of

1 (32.2 mg, 0.222 mmol) and pyridine (0.11 mL of a 1M chlorobenzene solution) were dissolved in dry chlorobenzene and refluxed with the solution turning from colorless to yellow orange with an orange precipitate forming after 30 minutes. After refluxing for 4 hours, the orange precipitate (2.2) was collected. Yield: 15.9 mg, 23.0%. 1H NMR (300

MHz, DMSO + 3 drops of trimethylamine which was added to inhibit decomposition) δ =

10.48 (s, 1H, imine proton, lower integration due to exchange), 8.19-8.21 (m, 1H), 7.96-

7.98 (m, 2H), 7.81-7.84 (m, 2H) ,7.60-7.62 (m, 4H), 7.53-7.56 (m, 2H), 7.38-7.40 (m, 2H).

MALDI mass spectroscopy (positive ion) [M+H-py]+ calculated m/z = 544.0419, found

-1 m/z=544.0413. IR spectrum: ν(CO) 2008, 1889 cm . UV-visible spectrum: λmax 428nm,

-1 -1 ε 1981 M cm . Elemental analysis C24H15N6O3Re1 3.7 H2O; found, C, 41.15%; H, 2.78%;

N, 12.99%; calculated C, 41.88%; H, 3.28%; N, 12.21%.

Synthesis of 2.3 and 2.4: Re(CO)5Cl (43.0 mg, 0.119 mmol) and 1 (33.7 mg , 0.232 mmol) were refluxed in wet chlorobenzene for 3 hours with the solution turning from colorless to yellow orange. Pyridine (0.11 mL of a 1M chlorobenzene solution) was added and the reaction refluxed for another 3 hours. The reaction was filtered and the solvent removed by rotary evaporation. The crude product mixture of 2.3 and 2.4 was then dissolved in

CH2Cl2, and eluted using CH2Cl2 on activity III basic alumina with the dioxo complex 2.4 eluting before the imino oxo complex 2.3. 2.3: Yield: 7.1 mg, 9.8%. 1H NMR (500 MHz,

CDCl3) δ = 9.93 (s, 1H), 8.80 (d, J = 6.0 Hz, 1H), 8.60 (d, J = 6.5 Hz, 1H), 8.05-8.00 (m,

1H), 7.91-7.85 (m, 2H), 7.71-7.66 (m, 5H), 7.36 (t, J = 6.5 Hz, 2H), 7.22 (t, J = 6.5 Hz,

1H). ESI mass spectroscopy (positive ion) [M+H]+ calculated m/z = 623.0603, found m/z

-1 = 623.9698. IR spectrum: ν(CO) 2011, 1874 cm . UV-visible spectrum: λmax 487 nm, ε

3 -1 -1 1 1.8 x 10 M cm . 2.4: Yield: 13.9 mg, 19.1%. H NMR (300MHz, CDCl3) δ = 8.79 (d, J

= 5.1 Hz, 2H), 8.01-7.96 (m, 2H), 7.89-7.83 (m, 2H), 7.73-7.63 (m, 4H), 7.36 (t, J =

7.5 Hz, 2H) 7.20 (t, J = 6.6 Hz, 1H). ESI mass spectroscopy (positive ion) [M+H]+ calculated m/z = 625.0522, found m/z = 625.0599 IR spectrum: ν(CO) 2007, 1871 cm-1.

3 -1 -1 UV-visible spectrum: λmax 518 nm, ε 2.4 x 10 M cm . Elemental analysis

C24H13N4O5Re10.9 H2O1.15 CH2Cl2 found, C, 40.77%; H, 2.12%; N, 7.81%; calculated

C, 40.96%; H, 2.34%; N, 7.60%.

Synthesis of 2.5: Compound 2.5 was produced and purified in an identical fashion as compound 2.2 but an N-methyl imidazole solution (0.11 mL of a 1M chlorobenzene solution) was used in place of pyridine. Yield: 7.9 mg, 11%. 1H NMR spectra were not obtained due to decomposition in solution. ESI mass spectroscopy (positive ion) [M+H-

MeIm]+ calculated m/z = 544.0419, found m/z = 544.0485 IR spectrum: ν(CO) 2004, 1896

-1 3 -1 -1 cm . UV-visible spectrum: λmax 428 nm, ε 1.6 x 10 M cm . Elemental analysis

C23H16N7O3Re1 0.7 C6H5Cl2.35 H2O found, C, 43.99%; H, 3.50%; N, 13.29%; calculated

C, 43.81%; H, 3.27%; N, 13.15%.

Synthesis of 2.6 and 2.7: Compounds 2.6 and 2.7 were produced in an identical fashion as compounds 2.3 and 2.4 but an N-methyl imidazole solution (0.11 mL of a 1M chlorobenzene solution) was used. 2.6: Yield: 5.6 mg, 7.7%. 1H NMR (300 MHz, DMSO)

δ = 11.55 (s, 1H), 8.15 (d, 1H), 8.05-7.89 (br m, 8H), 7.08 (br, 1H), 6.77 (br, 1H), 3.54 (s,

3H). ESI mass spectroscopy (positive ion) [M+H]+ calculated m/z = 627.0791, found m/z

-1 = 626.0685 IR spectrum: ν(CO) 2007, 1892 cm . UV-visible spectrum: λmax 488 nm, ε 1.8

3 -1 -1 1 x 10 M cm . 2.7: Yield: 19.2 mg, 26.3% . H NMR (300 MHz, CDCl3) δ = 8.04-7.99 (m,

2H), 7.84-7.81 (m, 2H), 7.67-7.62 (m, 4H), 7.57 (br, 1H), 6.93 (br, 1H), 6.66 (br, 1H), 3.59

(s, 3H). MALDI mass spectroscopy (positive ion) [M+H-MeIm]+ calculated m/z =

546.010, found m/z = 545.951. IR spectrum: ν(CO) 2010, 1878 cm-1. UV-visible spectrum:

3 -1 -1 λmax 520 nm, ε 1.9 x 10 M cm . Elemental analysis C23H14N5O5Re11.4 H2O0.2C4H7N2 found, C, 42.54%; H, 2.43%; N, 11.33%; calculated C, 42.82%; H, 2.73%; N, 11.33%.

Table 2.1: Crystal data and structure refinement for 2.2

Compound 2.2 Empirical formula C24 H15 N6 O3 Re Formula weight 631.62 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 a = 8.684(5) Å α =100.631(6)° Unit cell dimensions b = 11.159(7) Å β = 104.252(5)° c = 12.417(8) Å γ = 106.424(6)° Volume 548.61(15) Å3 Z 2 Density (calculated) 1.919 Mg/m3 Absorption coefficient 5.688 mm-1 F(000) 600 Crystal size 0.17 x 0.12 x 0.09 mm3 Theta range for data collection 1.76 to 25.13° Index ranges -10<=h<=10, -13<=k<=13, -14<=l<=14 Reflections collected 7840 Independent reflections 3786 [R(int) = 0.1166] Completeness to theta = 59.96° 98.2 % Absorption correction SADABS Max. and min. transmission 0.6285 and 0.4448 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3786 / 0 / 307 Goodness-of-fit on F2 1.062 Final R indices [I>2sigma(I)] R1 = 0.0371, wR2 = 0.0917 R indices (all data) R1 = 0.0441, wR2 = 0.0945 Largest diff. peak and hole 2.484 and -1.414 e.Å-3

Table 2.2: Crystal data and structure refinement for 2.4

Compound 2.4 Empirical formula C24 H13 N4 O5 Re Formula weight 623.58 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 a = 8.665(9) Å α =101.488(11)° Unit cell dimensions b = 11.112(11) Å β = 104.233(11)° c = 12.398(13) Å γ = 105.919(11)° Volume 1066.5(19) Å3 Z 2 Density (calculated) 1.942 Mg/m3 Absorption coefficient 5.743 mm-1 F(000) 600 Crystal size 0.25 x 0.22 x 0.14 mm3 Theta range for data collection 1.77 to 25.13° Index ranges -10<=h<=10, -13<=k<=13, -14<=l<=14 Reflections collected 7667 Independent reflections 3778 [R(int) = 0.0431] Completeness to theta = 59.96° 98.9 % Absorption correction SADABS Max. and min. transmission 0.7452 and 0.5438 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3778 / 0 / 307 Goodness-of-fit on F2 1.032 Final R indices [I>2sigma(I)] R1 = 0.0427, wR2 = 0.1052 R indices (all data) R1 = 0.0492, wR2 = 0.1097 Largest diff. peak and hole 3.365 and -2.110 e.Å-3

Table 2.3: Crystal data and structure refinement for 2.5

Compound 2.5 Empirical formula C46 H32 N14 O6 Re2 Formula weight 1249.26 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 a = 8.4924(3) Å α = 81.245(2)° Unit cell dimensions b = 13.9775(5) Å β = 86.660(2)° c = 18.5942(6) Å γ = 79.716(2)° Volume 2145.32(13) Å3 Z 2 Density (calculated) 1.934 Mg/m3 Absorption coefficient 5.707 mm-1 F(000) 1208 Crystal size 0.38 x 0.24 x 0.17 mm3 Theta range for data collection 1.50 to 25.09° Index ranges -10<=h<=10, -16<=k<=16, -22<=l<=22 Reflections collected 32040 Independent reflections 7584 [R(int) = 0.0350] Completeness to theta = 59.96° 99.6 % Absorption correction SADABS Max. and min. transmission 0.4509 and 0.2222 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 7584/ 12 / 619 Goodness-of-fit on F2 0.987 Final R indices [I>2sigma(I)] R1 = 0.0423, wR2 = 0.1072 R indices (all data) R1 = 0.0460, wR2 = 0.1101 Largest diff. peak and hole 6.632 and -2.199 e.Å-3

Table 2.4: Crystal data and structure refinement for 2.6

Compound 2.6 Empirical formula C46 H30 N12 O8 Re2 Formula weight 1251.22 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 a = 8.4650(8) Å α = 81.483(4)° Unit cell dimensions b = 13.9288(14) Å β = 86.727(4)° c =1 8.5509(19) Å γ = 79.979(4)° Volume 2127.8(4) Å3 Z 2 Density (calculated) 1.953 Mg/m3 Absorption coefficient 5.756 mm-1 F(000) 1208 Crystal size 0.21 x 0.12 x 0.09 mm3 Theta range for data collection 1.74 to 25.10° Index ranges -10<=h<=10, -16<=k<=16, -22<=l<=21 Reflections collected 34543 Independent reflections 7464[R(int) = 0.0320] Completeness to theta = 59.96° 98.7 % Absorption correction SADABS Max. and min. transmission 0.7452 and 0.5781 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 7584/ 12 / 619 Goodness-of-fit on F2 1.019 Final R indices [I>2sigma(I)] R1 = 0.0367, wR2 = 0.0933 R indices (all data) R1 = 0.0475, wR2 = 0.1047 Largest diff. peak and hole 3.431 and -2.296 e.Å-3

Table 2.5: Crystal data and structure refinement for 2.7

Compound 2.7 Empirical formula C23 H14 N5 O5 Re Formula weight 626.59 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P2(1)/c a = 8.4859(5) Å α = 90° Unit cell dimensions b = 11.2320(6) Å β = 97.282(2)° c = 22.2437(13) Å γ = 90° Volume 2127.8(4) Å3 Z 4 Density (calculated) 1.979 Mg/m3 Absorption coefficient 5.827 mm-1 F(000) 1208 Crystal size 0.21 x 0.12 x 0.09 mm3 Theta range for data collection 1.74 to 26.10° Index ranges -10<=h<=10, -13<=k<=13, -23<=l<=27 Reflections collected 16502 Independent reflections 4176 [R(int) = 0.0363] Completeness to theta = 59.96° 99.9 % Absorption correction SADABS Max. and min. transmission 0.6018 and 0.2120 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4176 / 0 / 308 Goodness-of-fit on F2 1.280 Final R indices [I>2sigma(I)] R1 = 0.0223, wR2 = 0.0437 R indices (all data) R1 = 0.0268, wR2 = 0.0450 Largest diff. peak and hole 1.173 and -1.154 e.Å-3

Results and Discussion

Re(CO)5Cl was reacted with two equivalents of diiminoisoindoline in refluxing wet

(i.e. not dried) chlorobenzene and the solution turns red-purple as the reaction proceeded

(Figure 2.1). Either pyridine or N-methyl imidazole was added to the reaction solution, resulting in the formation of colored (orange, red and purple) products that could be purified via chromatography using activity III basic alumina with dichloromethane as the eluent. The products (compounds 2.2-2.7) were characterized and five of the six were structurally elucidated by X-ray crystallography; their structures are shown in Figure 2.2.

As shown in the scheme, three types of aza(dibenzo)dipyrromethene ligands are formed: a bis(imino) terminated chelate, a bis(oxo) terminated chelate, and a mixed imino/oxo chelate. In all cases, the Re(I) ion is coordinated by the planar bidentate aza(dibenzo)dipyrromethene unit, and the remainder of the coordination sphere is occupied by three facial carbonyl ligands and either a pyridine (2.2-2.4) or N-methyl imidazole (2.5-2.7) unit in the remaining position. The formation of the oxo terminated products results from the presence of water in the solution; the use of distilled and dried chlorobenzene/methanol results in the production of only the imino terminated products

2.2 and 2.5. The imine terminated compounds were unstable to hydrolysis and subsequent decomposition. The N-methyl imidazole terminated compound 2.5 in particular is very unstable in solution, although we were able to characterize it in the solid state.

Figure 2.2: The crystal structures of 2.2-2.7 with 35% thermal ellipsoids. Hydrogen atoms have been omitted for clarity. The X-ray structures of the two pyridine and three N-methyl imidazole complexes reveal some diagnostic bond features as well as parameters that are common for Re(CO)3 complexes. The aza(dibenzo)dipyrromethene carbonyl bond lengths of compounds 2.4 and

2.7 are shorter than the imine bonds in 2.2 and 2.5. The aza(dibenzo)dipyrromethene unit is planar, and the chelate binds to the Re(I) centre symmetrically, with Re-N bond lengths of 2.165(7) Å and 2.166(6) Å for 2.2 and 2.164(3) Å and 2.161(2) Å for 2.5. The axial Re-

N distances are only slightly longer, measuring 2.221(7) Å for 2.2 and 2.193(2) Å for 2.4.

The Re-C and C-O distances of the metal carbonyl units are typical for Re(CO)3 complexes.339–342

I 6 Re (CO)3 complexes are low spin d metal systems, and thus these diamagnetic compounds can be readily characterized by NMR, although their solubilities are limited.

In the 1H NMR spectrum, we observed the expected complex splitting for the isoindoline units as well as the axial ligand signals for either pyridine in 2.2-2.4 or N-methyl imidazole in 2.5-2.7. In the compounds with the terminal imine groups (2.2, 2.3, 2.5 and 2.6), we observe the NH resonances as well. The IR spectra for compounds 2.2-2.7 show several diagnostic stretches for the terminal aza(dibenzo)dipyrromethene functional groups and the metal coordination geometry. The Re(CO)3 unit shows a1 and e type CO stretches that result from the local C3v environment of the facial arrangement of the carbonyl units, with frequencies that range from ~2005-2007 and ~1860-1880 cm-1, respectively. The identity of the terminal functional groups (oxo or imino) can also be determined from the IR spectrum; the oxo stretches appear at ~1740 cm-1 whereas the imino stretches appear at

~1630 cm-1.

Compounds 2.2-2.7 absorb light in the visible region, and the UV-visible spectra of

2.2-2.4 in dichloromethane are shown in Figure 2.3. Compounds 2.5-2.7 exhibit analogous spectra (Figure 2.4). The transitions are typical for metal-to-ligand charge transfer (MLCT) bands, and the nature of these transitions was confirmed by solvent polarity studies

(Appendix A). We observe a bathochromic shift of approximately 25 nm from highly nonpolar solvents, such as toluene, to polar solvents like DMSO. The extinction coefficients, which are in the range of 1500-2000 M-1-cm-1 are also consistent with a MLCT transition.

Figure 2.3: Uv-Visible spectra of 2.2-2.4 in dichloromethane.

Figure 2.4: Uv-Visible spectra of 2.5-2.7 in dichloromethane.

Compounds 2.2-2.7 were also investigated via cyclic voltammetry, and we observe some notable differences between the bis(imino) compounds 2.2 and 2.5 versus the oxo/imino (2.3 and 2.6) and bis(oxo) compounds (2.4 and 2.7). Cyclic voltammetry experiments were carried out in DMF using tetrabutylammonium hexafluorophosate as the electrolyte. Figure 2.5 shows the votammagrams for compounds 2.2-2.4; compounds 2.4-

2.7 show identical features and trends (Figure 2.6). We observe semi-reversible reductions that become more negative as one goes from bis(imine) 2.2 to imino/oxo compound 2.3.

Bis(oxo) compound 2.4 shows a further progression of this reduction wave and exhibits an additional semi-reversible reduction at more positive potential, (approximately -0.45 V) which we hypothesize is a ligand-based reduction. The conversion of imine to oxo functional groups moves the reduction potential to more negative values, which corresponds to stabilization of the HOMO orbitals in these compounds. This phenomenon corresponds well to the red shifts observed in the UV-visible spectra (Figures 2.3 and 2.4).

Figure 2.5: Cyclic volatmmograms of compounds 2.2-2.4 in DMF.

Figure 2.5: Cyclic volatmmograms of compounds 2.5-2.7 in DMF.

Conclusion

In conclusion, we have shown that half phthalocyanine-like chelates can be produced by condensing two equivalents of the phthalocyanine precursor diiminoisoindoline with Re(CO)5Cl as a templating agent. The resultant products show

MLCT type absorptions in their UV-visible spectra, as seen in Re(CO)3 diimine complexes.

The wavelengths of absorption are dependent on the identity of the terminal groups, with red shifts observed when an oxo group replaces an imine group. We are continuing our work on developing new methods for the synthesis of novel compounds based upon diiminoisoindoline, including both macrocycles and chelates.

CHAPTER III

BORON TEMPLATED SYNTHESIS OF A BODIPY ANALOGUE FROM A PHTHALOCYANINE PRECURSOR

DOI: 10.1039/c6nj00085a

Introduction

As research into the BODIPY class of compounds (Figure 3.1) progresses with continued interest, many groups have begun to investigate the synthesis of alternate boron-based fluorophores.243,247,274,278,286 Much of this chemistry remains unexplored, although significant work has been carried out on aza-BODIPY systems, also shown in Figure 3.1.

One basic modification of the BODIPY molecule is to replace the pyrrole ring with an isoindoline; this simple modification along with the introduction of a nitrogen atom at a meso-position results in a “phthalocyanine-like” BODIPY analog. In this communication, we present a simple boron template method for the construction of aza(dibenzopyrro)methane diphenylboron complexes (Scheme 3.1). Under dry conditions, a bis(imino) terminated complex 1 is produced, but under non-anhydrous conditions a mixture of the bis imino, bis oxo and mixed iminooxo compounds (1-3) form. The resultant

89 complexes have been fully characterized, the photophysics probed, and DFT/TDDFT calculations done in order to gain insight into their unique properties. Most notably, compounds 3.1-3.3 exhibit very large Stokes shifts in their emission spectra.

Figure 3.1: The structures of BODIPY (left) and aza-BODIPY (right).

Scheme 3.1: The reaction to form compounds 3.1-3.3.

Unlike the BODIPY and azaBODIPY classes of compounds, there has been much less study into the isoindoline based aza(dibenzopyrro)methene (ADBM) family of molecules. Several years ago, Lukyanets and Kobayashi 290 presented the synthesis of aryl substituted ADBMs using Grignard reagents and phthalonitrile, based on work by

Bredereck and Vollmann.289 Since then, there has been several reports on the chemistry of

297,333–336,343–353 aryl substituted ABDMs as well as their BF2 and metal complexes. Since then, Cammidge and coworkers synthesized an alkene terminated ADBM via the condensation of two alkeneiminoisoindolines.292 More recently, Li and co-workers presented the synthesis of asymmetric isoindoline based chelates using phthalonitrile as the starting material.337 For several years, we worked on the chemistry of phthalocyanine

90 analogs and chelate systems incorporating diiminoisoindoline

(DII).169,174,189,190,227,228,339,354,355 Both types of compounds can be synthesized using template methods. Therefore, we surmised that a ADBM might also be produced from simple isoindoline starting materials using a templating agent that prevented ring formation.

Experimental

General Information

All reagents and starting materials were purchased from commercial vendors and used without further purification. 1,3-diiminoisoindoline was synthesized according to a previously published procedure.164 Chlorobenzene was stored over 3 Å molecular sieves.

Column chromatography was performed on silica gel (Dynamic Adsorbents, Inc, 63-200

μm). Deuterated solvents were purchased from Cambridge Isotope Laboratories and used as received.

NMR spectra were recorded on 300 or 500 MHz spectrometers, Chemical shifts were given in ppm relative to residual solvent resonances (1H, 13C NMR spectra). High resolution mass spectrometry experiments were performed on a Bruker MicroTOF-III instrument. Infrared spectra were collected on Thermo Scientific Nicolet iS5 which was equipped with an iD5 ATR.

X-ray intensity data were measured on a Bruker CCD-based diffractometer with dual Cu/Mo ImuS microfocus optics (Cu Kα radiation, λ = 1.54178 Å, Mo Kα radiation, λ

=0.71073 Å). Crystals were mounted on a cryoloop using Paratone oil and placed under a steam of nitrogen at 100 K (Oxford Cryosystems). The detector was placed at a distance of

5.00 cm from the crystal. The data were corrected for absorption with the SADABS

91 program. The structures were refined using the Bruker SHELXTL Software Package

(Version 6.1), and were solved using direct methods until the final anisotropic full-matrix, least squares refinement of F2 converged.

UV-Vis spectra were recorded on a Hitachi UV-Vis spectrophotometer (U-3010).

Fluorescence excitation and emission data in solution were recorded on a Horiba Jobin-

Yvon FluoroMax-4 fluorescence spectrophotometer using Coumarin 540 in methanol as a standard. All slit widths were held constant at 5 nm. The quantum yields in solution were

2 퐺푟푎푑푥 휂푥 calculated using the following equation: 훷푥 = 훷푠푡 2 ; ηx = 1.324, ηst = 1.329; Φst = 퐺푟푎푑푠푡 휂푠푡

0.46 and Grad the gradient from the plot of integrated fluorescence intensity vs absorbance.231

Cyclic voltammograms were obtained using a standard three electrode cell and electrochemical analyser BAS 100B from Bioanalytical systems and were recorded at 298

K under the following conditions: 10-3 M samples in dried acetonitrile in the presence of

0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as a supporting electrolyte,

Ag/Ag+ reference electrode, 0.79 mm2 gold working electrode, and platinum wire auxiliary electrode. The working electrode was polished first with 3 µm fine diamond, then 0.05 µm alumina. The electrode was rinsed with ethanol and deionized water after each polishing and wiped with a Kimwipe. The non-aqueous Ag/Ag+ reference was prepared by soaking the silver wire in the degassed and dried THF solution of 5% Acetonitrile: 0.01M AgClO4:

+ 0.1M TBAPF6. At a 0.10 V/s sweep rate, the Fc/Fc occurs at 0.060 ±0.005 V (∆Ep =

119mV; ipa/ipc = 0.99).

All DFT calculations were conducted using the Gaussian 09 software.356 All of the geometries were optimized at the DFT level using the TPSSh exchange-correlation

92 functional and the 6-31G(d) basis set was used for all atoms.357,358 The PCM method was used to calculate the solvent effects for all the DFT and TDDFT calculations using DCM as a solvent.359–361 The first 40 states were calculated for the TDDFT calculations.

Molecular orbital contributions were compiled from single-point calculations using the

QMForge program.362

Synthesis of 3.1-3.3:

Synthesis of 3.1 and 3.2:Ph3B (0.097 g ,0.401 mmol) and 1,3-diiminoisoindoline

(DII) (0.111 g, 0.765 mmol) were refluxed in dry chlorobenzene for 12 hours with the solution turning from clear to yellow-green. The chlorobenzene was removed, and the remaining solid purified via column chromatography on silica using CH2Cl2 as the eluting

-1 -1 solvent. 3.1: Yield: 77 mg, 46%. λmax = 333 nm, ε = 23,000 M cm , λmax = 426 nm, ε =

-1 -1 -2 6,700 M cm , excitation at 426 nm ,λem = 482 nm, 512 nm Φ = 2.5×10 . IR: ν C=N 1657

-1 1 cm . H NMR (300 MHz, CDCl3) δ = 9.06 (s, 2H), 8.15-8.12 (m, 2H), 7.96-7.93 (m, 2H),

13 7.76-7.68 (m, 5H), 7.54-7.52 (m, 4H), δ = 7.36-7.26 (m, 6H). C NMR (300 MHz, CDCl3)

δ = 184.54, 180.37, 169.38, 161.10, 136.10, 134.23, 133.68, 132.15, 132.36, 127.55,

123.99, 123.16. ESI MS calcd for C28H22BN5 m/z = 439.1963, found 439.1968. 3.2: Yield:

-1 -1 -1 -1 23 mg, 13.7%, λmax = 340 nm, ε = 25,000 M cm , λmax = 433 nm, ε = 5,300 M cm .

-2 -1 Excitation at 433 nm, λem = 481 nm, 511 nm, Φ = 5.8×10 . IR: ν C=O 1760 cm , C=N

1659 cm-1, 1H NMR (300 MHz, d6-DMSO) δ = 11.69(s, 1H), 8.17 (t, J= 5.40 Hz, 2H),

8.08 (d, J = 6.90 Hz, 1H), 7.90-7.77 (m, 5H), 7.52 (d, J = 7.5Hz, 4H), 7.28-7.06 (m, 6H).

13 C NMR (300 MHz, CDCl3) δ = 134.86, 133.68, 133.77, 133.7, 132.31, 127.65, 126.93,

124.46, 124.38, 124.20. ESI MS calcd for C28H20BN4O m/z = 439.1725, found m/z =

439.1730.

Synthesis of 3.3: PhB(OH)2 (0.241g, 1.98 mmol) and DII (0.274g, 1.89 mmol) were refluxed in chlorobenzene that had not been dried over molecular sieves for 72 h. The chlorobenzene was removed and the residue was purified by column chromatography on silica, using CH2Cl2 as the elution solvent. This reaction also produces compounds 3.1 and

-1 -1 3.2, but in lower yield. Yield: 3.0 mg, 0.36%, λmax = 348 nm, ε = 25,000 M cm , λmax =

-1 -1 -3 440 nm, ε = 5,100 M cm . Excitation at 440 nm, λem = 492 nm, 515nm Φ = 5.6×10 IR:

-1 1 ν C=O 1759 cm , H NMR (300 MHz, CDCl3) δ = 8.18-8.15 (m, 2H), 7.81-7.77 (m, 6H),

13 7.61 (dd, J = 4.50, 7.80, 4H), 7.31-7.19 (m, 6 H). ). C NMR (500 MHz, CDCl3) δ =

164.39, 164.15, 164.08, 164.02, 134.46, 134.22, 134.12, 133.77, 133.53, 133.29, 133.26,

133.15, 132.65. ESI MS calcd for C28H18BN3O2 m/z = 440.1565, found m/z = 440.1570.

Table 3.1: Crystal data and structure refinement for 3.1

Compound 3.1

Empirical formula C28 H20 B N5 Formula weight 437.30 Temperature 100(2) K Wavelength 1.54718 Å Crystal system Monoclinic Space group P2(1)/c a = 16.5717(10) Å α = 90° Unit cell dimensions b = 22.3081(13) Å β = 99.701(4)° c = 11.7698(7) Å γ = 90° 3 Volume 4288.9(4) Å Z 8 Density (calculated) 1.354 Mg/m3 Absorption coefficient 0.641 mm-1 F(000) 1824 Crystal size 0.27× 0.18 × 0.11 mm3 Theta range for data collection 2.70 to 62.99° Index ranges -17<=h<=19, -12<=k<=25,-13<=l<=13 Reflections collected 25267 Independent reflections 6842 [R(int) = 0.0337] Completeness to theta 98.6 % Absorption correction SADABS Max. and min. transmission 0.7527 and 0.6871 Refinement method Full-matrix least-squares on F2 Data / restraints / 6842 / 0 / 613 parameters Goodness-of-fit on F2 0.962 Final R indices R1 = 0.0403, [I>2sigma(I)] wR2 = 0.0898 R1 = 0.0563, R indices (all data) wR2 = 0.0993 Largest diff. peak and hole 0.514 and -0.392 e.Å-3

Table 3.2: Crystal data and structure refinement for 3.2

Compound 3.2 Empirical formula C29 H21 B Cl2 N4 O Formula weight 524.19 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 a = 8.8161(5)Å α = 78.972(2)° Unit cell dimensions b = 10.6099(6) Å β = 86.357(3)° c = 13.5285(8) Å γ = 84.254(4)° Volume 1235.06(12) Å3 Z 2 Density (calculated) 1.407 Mg/m3 Absorption coefficient 0.295 mm-1 F(000) 540 Crystal size 0.29 × 0.18 × 0.09 mm3 Theta range for data 1.53 to 26.167° collection Index ranges -10<=h<=10, -13<=k<=12,-16<=l<=16 Reflections collected 14690 Independent reflections 4687 [R(int) = 0.0833] Completeness to theta 97.9 % Absorption correction SADABS Max. and min. transmission 0.7452 and 0.5357 Refinement method Full-matrix least-squares on F2 Data / restraints / 4687 / 0 / 335 parameters Goodness-of-fit on F2 1.043 Final R indices R1 = 0.0621, [I>2sigma(I)] wR2 = 0.1549 R1 = 0.1941, R indices (all data) wR2 = 0.1732 Largest diff. peak and hole 1.045 and -1.093 e.Å-3

Table 3.3: Crystal data and structure refinement for 3.3

Compound 3.3 Empirical formula C29 H20 B Cl2 N3 O2 Formula weight 524.19 Temperature 100 (2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 a = 8.7931(11) Å α = 78.771(5)° Unit cell dimensions b = 10.5963(13) Å β = 86.503(6)° c = 13.5308(18) Å γ = 84.592(6)° Volume 1229.9(3) Å3 Z 2 Density (calculated) 1.415 Mg/m3 Absorption coefficient 0.298 mm-1 F(000) 540 Crystal size 0.27 × 0.24 × 0.21 mm3 Theta range for data 1.99 to 26.376° collection Index ranges -10<=h<=10, -13<=k<=11, -15<=l<=16 Reflections collected 16216 Independent reflections 4790 [R(int) = 0.0355] Completeness to theta 97.4 % Absorption correction SADABS Max. and min. transmission 0.7454 and 0.6416 Refinement method Full-matrix least-squares on F2 Data / restraints /parameters 4790 / 0 / 334 Goodness-of-fit on F2 1.080 Final R indices R1 = 0.0572, [I>2sigma(I)] wR2 = 0.1466 R1 = 0.0734, R indices (all data) wR2 = 0.1611 Largest diff. peak and hole 1.033 and -0.910 e.Å-3

Results and Discussion

For our study, we decided to use the phthalocyanine precursor DII and phenylboronic acid as a boron-centered template. The boron halides BCl3 and BBr3 are used as templates for the formation of subphthalocyanine from phthalonitrile.91,97,98,363 This contracted phthalocyanine analog forms due to the lability of the boron-halide bonds and is isolated after long reaction times; we wanted to avoid subphthalocyanine formation in our reactions. Therefore, we decided to employ a boron-based template with a more covalent (B-C) bond as well as a pre-activated form of phthalonitrile (DII). The reaction of two equivalents of

DII with phenylboronic acid produces the products shown in Scheme 3.1, where the boron has disproportionated to afford bisphenyl ADBM products as well as boronic acid. Reducing the amount of DII to one equivalent increases the yields of the three products. Alternatively, we can avoid the disproportionation reaction entirely if we use triphenylboron as the source of the main group element; reaction of this species with two equivalents of DII produces the same products as observed for the phenylboronic acid. For both reactions, we can isolate the products via column chromatography using silica as the solid phase and methylene chloride as the eluent.

The reaction with triphenyl boron produces compounds 3.1 and 3.2, while the phenylboronic acid affords all three compounds. Yields decrease as the terminal nitrogen atoms are replaced with oxygen atoms.

We were able to structurally characterize compounds 3.1-3.3 using single crystal X-ray diffraction and their structures are shown in Figure 3.2. As can be seen in the figure, the three compounds are identical with the exception of the

98 terminal heteroatom positions. The chelate itself is composed of two isoindoline rings linked by a bridging nitrogen atom. The ABDM ligand itself is planar and bidentate, with the central isoindoline nitrogen atoms bound to the metal centre. The observed planarity is in good agreement with the proposed delocalized electronic structure of the chelate. All three compounds have an identical coordination environment immediately around the boron centre, with two phenyl rings and two nitrogen atoms from the ABDM ligand. Compound 3.1 shows the greatest variance in B-N bond lengths, ranging from 1.584(3) to 1.595(3) Å, but in all three the average B-N length is observed to be ~1.590 Å. The C-N bonds of the six membered chelate ring with the B(Ph)2 unit are on the range of ~1.34 Å, and the phenyl rings of the isoindoline units exhibit expected bond lengths for an aromatic ring system of ~1.39 Å.

Figure 3.2: The structures of 2-7 with 35% thermal ellipsoids. Hydrogen atoms have been omitted for clarity.

Compounds 3.1-3.3 were investigated for both their absorption and emission, which are shown in Figure 3.3. The absorption spectra in acetonitrile exhibit two features: an intense (ε ~25,000 M-1·cm-1) absorption in the UV and a weaker (ε

~5000-6000 M-1·cm-1) band in the visible region. These two bands bathochromically shift as the terminal heteroatom positions change from nitrogen to oxygen. The more intense band shifts from 333 to 340 to 348 nm as the terminal atoms change from N,N, to N,O and finally O,O groups with a similar progression observed in the lower energy bands (426, 433, 440 nm) for 3.1, 3.2 and 3.3 respectively. All three compounds are fluorescent when irradiated at the lower energy band, although they show modest but greatly varying quantum yields of emission depending on the identity of the terminal heteroatoms. Compound 3.2, with terminal N,O groups, displays the highest quantum yield at 5.8%, followed by

3.1 (N,N) at 2.5% and 3.3 (O,O) at 0.56%. The Stokes shifts for these compounds are much larger than those seen for the BODIPY class of fluorophores; we observe shifts of 56, 48, and 52 nm for 3.1, 3.2 and 3.3 respectively. These values are intermediate between those seen in Lukyanets and Kobayashi290 ADBMs and those observed by Cammidge in the alkene terminated systems.292 Additionally, the emission profiles for 3.1-3.3 are not the mirror images of the absorption spectra. We observed this phenomenon in the BOPHY chromophore,250 and this lack of symmetry could be indicative of a vibrational cooling process in the excited state dynamics.251 Compounds 3.1-3.3 are sensitive to photobleaching; we observe decomposition when exposed to light and air over the course of 24 hours. We also

100 investigated the electrochemistry of compounds 1-3; these data (Figure 3.4) reveal irreversible reduction processes in these compounds.

Figure 3.3: The normalized absorption (left) and emission (right) spectra for compounds 3.1-3.3 in acetonitrile. Compounds were excited at the lowest energy maxima for emission spectra.

101

Figure 3.4: Cyclic voltammongrams of 3.1, 3.2, and 3.3 in 0.1 M −1 TBAPF6/acetonitrile at 0.25 V/s and 10.0 μA V versus AgCl.

To elucidate the absorption spectra and to provide insight into the emission properties and electrochemistry, we carried out DFT and TDDFT calculations on compounds 3.1-3.3. Figures 3.5-3.10 show the DFT-predicted profiles of the frontier orbitals for compounds 3.1-3.3 and Figure 3.11 graphs their orbital energies. As can be seen in comparing the two figures, in compounds 3.1-3.3 the HOMO-3 through the HOMO are closely spaced in energy and similar in composition. These four orbitals are localized primarily on the BPh2 unit and are more than 80% phenyl in character. Only the HOMO-4 begins to have chelate character, which is primarily found on the heteroatoms of the chelate unit itself (~40%). The LUMO in compounds 3.1-3.3 are centred on the azaBODIPY core and unlike the HOMO in

3.1-3.3, the LUMO is energetically well-separated from other orbitals. Notably, the

102 energy of the LUMO decreases upon stepwise substitution of the terminal nitrogen atoms with oxygen atoms. We also calculated the visible spectra of these compounds using the TDDFT approach (Figure 3.12). The calculated spectra are in good agreement both in energies and in oscillator strengths with the experimentally derived spectra of 3.1-3.3. The lower energy bands in 3.1-3.3 can be assigned as primarily HOMO-4 to LUMO transitions. These bands thus do have some charge transfer character. The more intense UV bands can be assigned as predominantly π to π* transitions between the azaBODIPY-centred HOMO-5 and the π* LUMO.

Clearly, the presence of the five electronegative heteroatoms in the ligand backbone stabilizes the bonding π HOMO-5, which results in a significant blue shift in absorption relative to the BODIPY class of compounds.

Figure 3.5: Frontier orbital diagrams for 3.1.

103

Figure 3.6: Orbital compositions for 3.1.

Figure 3.7: Frontier orbital diagrams for 3.2.

104

Figure 3.8: Orbital compositions for 3.2.

Figure 3.9: Frontier orbital diagrams for 3.3.

105

Figure 3.10: Orbital compositions for 3.3.

Figure 3.11: DFT-predicted orbital energies of compounds 3.1-3.3.

106

Figure 3.12: Experimental and TDDFT-predicted UV-vis spectra of compounds 3.1 (left top), 3.2 (left bottom) and 3.3 (right).

Conclusion

In conclusion, we used a one-pot method for the synthesis of a BPh2 azadibenzopyrromethene complex. Depending on the degree of hydrolysis, three products can be isolated, with imine, oxo, or imino-oxo terminated positions. All three complexes have been crystallographically characterized, revealing planar chelates bound to a central

BPh2 unit. These compounds are mildly fluorescent, and exhibit large Stokes shifts relative to those seen in the related BODIPYs. We also probed their electronic structure with

TDDFT calculations, and observed that the presence of five heteroatoms in the chelate ring results in highly stabilized π systems and blue shifted absorption spectra relative to the

BODIPYs. We are continuing our work on the synthesis of templated chelates using isoindoline-based starting materials.

107

CHAPTER IV

STRUCTURE AND ELECTRONICS IN DIMERIC BORON Π EXPANDED AZINE

AND SALPHEN COMPLEXES

The text of this chapter is a reprint of the material as it appears in: Crandall, L.A.;

Dawadi, M.; Burrell, T.; Odoom, A.; Ziegler C.J. Photochem. Photobiol. Sci. 2017, 16,

DOI: 10.1039/C6PP00479B

Introduction

Recent work in chromophore synthesis has focused on the synthesis of organic fluorophores with large absorption cross sections and high quantum yields of emission for use in biological imaging, sensors, and organic electronics.232,236–

238,241,364–366 One of the most studied classes of fluorophores for these applications is the BODIPYs (boron-dipyrromethenes) due to their ease of synthesis and

108 modification, strong absorbance, and high quantum yield of emission.240,243,245,246,273

More recently, dimeric BF2 chromophores compounds have been synthesized as new fluorophores including bis-BODIPY complexes, 1,8-naphthyridine and nindigo

250–253,274,293– BF2 adducts, as well as our recently reported BOPHY fluorophore.

295,367,368 The bis-BODIPY complexes tend to have a bathochrominally shifted absorbance and emission profiles in comparison to the unsubstituted BODIPY

274,293–295 fluorophores. Both the bis-BF2 1,8-naphthyridine and BOPHY fluorophores exhibit a strong absorbance bands at around 430 nm and large quantum

250,296 yields of emission (ф = 0.97 and 0.92 respectively). Like bis BF2 1,8- naphthyridine and BOPHY, the bis BF2 nindigo has a strong red shifted absorbance

297 around 740 nm. While it is fluorescent, the bis BF2 nindigo adduct is less stable in solution and decomposes to the mono BF2 adduct over a period of a few days.

We have been investigating new ligand systems to afford dimeric BF2 fluorophores, and have turned our attention to the well-known salen class of chelates. Diphenol salen ((N,N’-bis(salicylaldehydo)ethylenediamine)) and its copper complex was first synthesized in 1889 by Combes.369 Since the first synthesis of salens class of ligands, the development of salen metal derivatives has focused on their utility as ligands in chiral catalysts for enantioselective syntheses.

While there are a large number of reports on metal based salen compounds,370–374 there has been much less work on the boron adducts of these chelates.307,308,375 There has been some work on the complexation of BF2 with salen type ligands, where the bridging unit is either a hydrazine or a phenylene diamine. The earliest report on a

BF2 salen compound was presented in 1973 by Umland and coworkers, who

109 presented a mono-BF2 adduct of a hydrazine-salen ligand system (Figure 4.1, compound 1).298 More recently, dimeric phenylene bridged salphen complexes have been synthesized and investigated.309,310,376 In this report, we investigate the synthesis of π expanded salphen-BF2 complexes that incorporate 2- hydroxynaphthaldimines (Figure 4.1) including hydrazine and phenylene diamine analogues with ortho, meta and para substitution patterns.

Figure 4.1: Azine, π expanded azine and π expanded salphen BF2 complexes.

We were also able to structurally characterize Umland’s mono-BF2 adduct, compound 1. The incorporation of this group expands the π system by a phenyl group on each end of the chromophore, which extends their absorption/emission characteristics to the red end of the spectrum. We have X-ray structural data on all adducts presented in this report, and have fully characterized their properties.

Additionally, we carried out DFT/TDDFT calculations on these compounds to elucidate their electronic structures.

110

Experimental

General Information

All reagents and starting materials were purchased from commercial vendors and used without further purification. Column chromatography was performed on silica gel (Dynamic Adsorbents, Inc., 63-200 μm). Deuterated solvents were purchased from Cambridge Isotope Laboratories and used as received.

NMR spectra were recorded on 300 or 500 MHz spectrometers, Chemical shifts were assigned in ppm relative to residual solvent resonances (1H, 13C NMR spectra).

High resolution mass spectrometry experiments were performed on a Bruker

MicroTOF-III instrument. X-ray intensity data were measured on a Bruker CCD- based diffractometer with dual Cu/Mo ImuS microfocus optics (Cu Kα radiation, λ

= 1.54178 Å, Mo Kα radiation, λ = 0.71073 Å). Crystals were mounted on a cryoloop using Paratone oil and placed under a steam of nitrogen at 100 K (Oxford

Cryosystems). The data were corrected for absorption with the SADABS program.

The structures were refined using the Bruker SHELXTL Software Package (Version

6.1), and were solved using direct methods until the final anisotropic full-matrix, least squares refinement of F2 converged.

UV-Visible spectra were recorded on a Hitachi UV-Vis spectrophotometer (U-

3010). Fluorescence excitation and emission data in solution were recorded on a

Horiba Jobin-Yvon FluoroMax-4 fluorescence spectrophotometer using quinine sulphate in 0.1 M H2SO4 as a standard. All slit widths were held constant at 1 nm.

The quantum yields in solution were calculated using the following equation: Φx =

111

2 2 Φst ([Grad]x/[Grad]st)(ηx )/(ηst ); ηst = 1.33; Φst = 0.52 and Grad is the gradient from the plot of integrated fluorescence intensity vs absorbance.231

For the calculations, the starting geometries of compounds 1-5 were taken from

X-ray structures. All compounds were optimized using TPSSh hybrid (10% Hartree-

Fock exchange) exchange correlation functional with 6-311G(d) basis set. Solvent effects were modelled using the PCM approach. Acetonitrile was used as a solvent in all of the single point PCM-DFT and PCM-TDDFT calculations. All computations were performed using the Gaussian 09 software package.356

Synthesis of Salen compounds:

Scheme 4.1: Synthesis of compounds 4.1-4.5.

The ligand precursors to the compounds presented in this report were synthesized according to previously established literature procedures.377,378 A typical procedure was as follows: Two equivalents of salicylaldehyde or 2- hydroxynapthylaldehyde and one equivalent of hydrazine or phenylene diamine

112 were dissolved in a minimum of ethanol with a few drops of acetic acid. After stirring at room temperature for 30 min., the precipitate was filtered and washed with cold methanol then dried overnight.

Synthesis of 4.1-4.5:

Compounds 4.1-4.5 were synthesized by reacting one equivalent of the salen ligand precursor with a 10 mole excess of DIPEA and a 15 mole excess of BF3•OEt2 in a minimum of dichloromethane at room temperature for 24 h. The reactions can be seen in Scheme 1. Compounds 4.1-4.3 and 4.5 precipitated from the reaction mixtures as yellow orange solids. The solids were collected by vacuum filtration and washed with dichloromethane. After drying, the solids were suspended in water and stirred for 30 min. to remove any excess DIPEA, filtered, and dried overnight.

Compound 4.4 did not form a precipitate from the reaction solution; the reaction mixture was washed with water and the organic layer dried over MgSO4 and the volume reduced. The reaction mixture was then purified by column chromatography on silica gel with dichloromethane as the eluting solvent.

1 Compound 4.1: Yield: 0.077 g (33.6%), H NMR (300 MHz; CDCl3) δ ppm:

10.55 (s, 1H), 9.21 (s, 1H), 8.64 (s, 1H), 7.70 (t, J = 7.3, 2H), 7.52 (q, J = 7.9, 3H),

13 7.17-6.99 (m, 4H). C NMR (300 MHz; CDCl3) δ ppm: 164.71, 161.05, 139.49,

134.97, 134.27, 133.45, 132.55, 132.06, 120.97, 120.31, 119.73, 117.53, 117.18. 19F

11 6 NMR (300 MHz; CDCl3) δ ppm: 131.44 (br. s). B NMR (500 MHz; d -DMSO) δ

4 -1 -1 ppm: 7.27 (s). λmax 358 nm, ε 2.1 x 10 M cm . HRMS (ESI): m/z calc. for

+ C14H12BF2N2O2 289.0960, found 289.1018 [M+H] .

113

Compound 4.2: Yield: 0.056 g, 28%. 1H NMR (300 MHz; d6-DMSO) δ ppm: 11.56

(s, 1H), 10.09 (s, 1H), 9.85 (s, 1 H), 8.97 (d, J = 8.79 Hz, 1H), 8.60 (d, J = 8.49 Hz,

1H), 8.34 (d, J = 9.09 Hz, 1H), 8.12 (d, J = 9.09 Hz, 1H), 8.02 (d, J = 9.57 Hz, 1H),

7.95 (d, J = 7.89 Hz, 1H), 7.76-7.65 (m, 2H) 7.56-7.45 (m, 2H) 7.35-7.30 (m, 2H).

13C NMR (300 MHz; d6-DMSO) δ ppm: 161.13, 160.47, 160.01, 156.78, 140.14,

136.17, 134.69, 132.23, 131.69, 131.28, 129.21, 129.12, 128.04, 127.82, 124.99,

124.05, 121.71, 121.32, 118.84, 118.42, 108.41, 107.07. 19F NMR (300 MHz; d6-

11 6 DMSO) δ ppm: 131.86 (br. s). B NMR (500 MHz; d -DMSO) δppm: 7.21 (s) λmax

3 -1 -1 3 -1 -1 340 nm, ε= 15x 10 M cm λmax 432 nm, ε= 38x 10 M cm . HRMS (ESI): m/z

+ calc. for C22H15BF2N2O2Na 411.1092, found 411.1129 [M+Na] .

1 Compound 4.3: Yield: 0.043 g (64%), H NMR (300 MHz; CDCl3) δ ppm:

9.29 (br. s, 2 H), 8.09 (d, J=8.5 Hz, 2 H), 7.96 (d, J = 9.1, 2 H), 7.79-7.76 (m, 2 H),

7.70 (d, J = 7.9, 2 H), 7.63-7.57 (m, 4 H), 7.43 (t, J = 8.2, 2 H), 7.07 (d, J = 9.4, 2

13 H). C NMR (500 MHz; CDCl3) δ ppm: 163.87, 142.00, 131.66, 130.03, 129.67,

19 129.26, 128.17, 127.92, 125.31, 120.00, 119.89. F NMR (300 MHz; CDCl3) δ

11 ppm: 132.20 (br. s). B NMR (500 MHz; CDCl3) δ ppm: 7.27 (s). λmax 344 nm,

-1 -1 3 -1 -1 ε = 26x 103 M cm , λmax 387 nm, ε = 25x10 M cm . HRMS (ESI): m/z calc. for

+ C28H18B2F4N2O2Na 535.1368, found 535.1382 [M+Na] .

Compound 4.4: Yield: 0.134 g, (84%), 1H NMR (300 MHz; d6-DMSO) δ ppm: 9.85 (br. s, 2H), 8.61 (d, J = 8.49 Hz, 2H), 8.40 (d, J = 9.06, 2H), 8.21 (s, 1H),

8.03 (d, J = 7.92, 2H), 7.89 (d, J = 7.35 Hz, 2H), 7.81-7.69 (m, 3H), 7.57 (t, J = 7.62,

2H), 7.37 (d, J = 9.09, 2H). 13C NMR, (300 MHz; d6-DMSO) δ ppm: 162.06, 143.

09, 141.53, 131.60130.16, 129.41, 127.76, 125.24, 124.17, 121.60, 119.68. 19F

114

NMR (300 MHz; d6-DMSO) δ ppm: 132.47 (br. s). 11B NMR (500 MHz; d6-DMSO)

3 -1 -1 3 - δ ppm: 4.43 (br. s). λmax 342 nm, ε = 20x 10 M cm λmax 400 nm, ε = 29x 10 M

1 -1 cm . HRMS (ESI): m/z calc. for C28H18B2F4N2O2Na 535.1368, found 535.1382

[M+Na]+.

Compound 4.5: Yield: 0.106 g (76%), 1H NMR (300 MHz; d6-DMSO) δ ppm: 9.80 (s, 2H), 8.62 (d, J = 8.2 Hz, 2H), 8.39 (d, J = 9.1 Hz, 2H), 8.03 (d, J =

7.32 Hz, 2H), 7.94 (s, 4H), 7.75 (t, J = 7.1 Hz, 2H), 7.58 (t, J = 7.3 Hz, 2H), 7.36 (d,

J = 9.1 Hz, 2H). %), 13C NMR (300 MHz; d6-DMSO) 161.85, 161.13, 142.28,

141.38, 131.64, 129.40, 27.78, 125.23, 125.03, 121.63, 119.68, 108.97. 19F NMR

(300 MHz; d6-DMSO) 132.51 (br. s). 11B NMR (500 MHz; d6-DMSO) 5.39 (br. s).

3 -1 -1 3 -1 -1 λmax 343 nm, ε = 20x 10 M cm λmax = 411 nm, ε = 35x10 M cm . HRMS (ESI):

+ m/z calc. for C28H18B2F4N2O2Na 535.1368, found 535.1382 [M+Na] .

115

Table 4.1: Crystal data and structure refinement for 4.1

Compound 4.1 Empirical formula C14 H11 B F2 N2 O2 Formula weight 288.06 Temperature 100(2) K Wavelength 1.54718 Å Crystal system Monoclinic Space group P 21/c a = 6.2396(2) Å α = 90° Unit cell dimensions b = 15.0244(5) Å β = 106.777(2) ° c = 13.6239(4) Å γ = 90° 3 Volume 1222.83(7) Å Z 4 Density (calculated) 1.565 Mg/m3 Absorption coefficient 1.066 mm-1 F(000) 592 Crystal size 0.143 x 0.105 x 0.083 mm3 Theta range for data 4.49 to 65.77° collection Index ranges -7<=h<=6, -17<=k<=15, -15<=l<=16 Reflections collected 7595 Independent reflections 2021 [R(int) = 0.0278] Completeness to theta 95.1 % Absorption correction SADABS Max. and min. 0.7527 and 0.6968 transmission Refinement method Full-matrix least-squares on F2 Data / restraints / 2021 / 0 / 190 parameters Goodness-of-fit on F2 1.081 Final R indices R1 = 0.0425, wR2 = 0.1365 [I>2sigma(I)] R indices (all data) R1 = 0.0453, wR2 = 0.1391 Largest diff. peak and hole 0.271 and -0.270 e.Å-3

116

Table 4.2: Crystal data and structure refinement for 4.2

Compound 4.2 Empirical formula C22 H15 B F2 N2 O2 Formula weight 388.17 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 a = 8.1614(12) Å α = 94.706(7)° Unit cell dimensions b = 9.4911(14) Å β = 101.989(5)° c = 11.3018(18) Å γ = 92.791(7)° 3 Volume 851.5(2) Å Z 2 Density (calculated) 1.514 Mg/m3 Absorption coefficient 0.112 mm-1 F(000) 400 Crystal size 0.49x 0.45 x 0.37 mm3 Theta range for data 1.85 to 25.15° collection Index ranges -9<=h<=9, -11<=k<=11, -13<=l<=13 Reflections collected 8627 Independent reflections 2951 [R(int) = 0.0453] Completeness to theta 96.7 % Absorption correction SADABS Max. and min. transmission 0.9596 and 0.9471 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2951/ 0 / 263 Goodness-of-fit on F2 1.128 Final R indices [I>2sigma(I)] R1 = 0.1410, wR2 = 0.4363 R indices (all data) R1 = 0.1486, wR2 = 0.4405 Largest diff. peak and hole 0.843 and -0.767 e.Å-3

117

Table 4.3: Crystal data and structure refinement for 4.3

Compound 4.3 Empirical formula C29 H20 B2 Cl2 F4 N2 O2 Formula weight 596.99 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 a = 11.2748(14) Å α = 110.390(3)° Unit cell dimensions b = 14.4752(18) Å β =90.141(3)° c = 17.300(2) Å γ = 100.184(3)° 3 Volume 2598.6(6) Å Z 4 Density (calculated) 1.526 Mg/m3 Absorption coefficient 0.312 mm-1 F(000) 1216 Crystal size 0.31x 0.30 x 0.16 mm3 Theta range for data 1.26 to 25.21° collection Index ranges -13<=h<=13, -17<=k<=17, -20<=l<=20 Reflections collected 31100 Independent reflections 9279 [R(int) = 0.0288] Completeness to theta 99.0 % Absorption correction SADABS Max. and min. 0.9527 and 0.9090 transmission Refinement method Full-matrix least-squares on F2 Data / restraints / 9279 / 0 / 739 parameters Goodness-of-fit on F2 1.067 Final R indices R1 = 0.0513, wR2 = 0.1447 [I>2sigma(I)] R indices (all data) R1 = 0.0654, wR2 = 0.1577 Largest diff. peak and hole 0.474 and -0.385 e.Å-3

118

Table 4.4: Crystal data and structure refinement for 4.4

Compound 4.4 Empirical formula C28 H18 B2 F4 N2 O2 Formula weight 512.06 Temperature 100(2) K Wavelength 1.54178 Å Crystal system Orthorhombic Space group Pcbn a = 10.5218(9) Å α = 90° Unit cell dimensions b = 12.6033(10) Å β = 90° c = 16.7317(15) Å γ = 90° 3 Volume 2218.8(3) Å Z 4 Density (calculated) 1.533Mg/m3 Absorption coefficient 1.002 mm-1 F(000) 1048 Crystal size 0.163x 0.117 x 0.073 mm3 Theta range for data 5.29 to 65.67° collection Index ranges -12<=h<=10, -14<=k<=13, -12<=l<=19 Reflections collected 12464 Independent reflections 1857 [R(int) = 0.0361] Completeness to theta 96.6 % Absorption correction SADABS Max. and min. 0.7527 and 0.6571 transmission Refinement method Full-matrix least-squares on F2 Data / restraints / 1857 / 0 / 173 parameters Goodness-of-fit on F2 1.067 Final R indices R1 = 0.0827, wR2 = 0.2133 [I>2sigma(I)] R indices (all data) R1 = 0.857, wR2 = 0.2147 Largest diff. peak and hole 0.407 and -0.294 e.Å-3

119

Table 4.5: Crystal data and structure refinement for 4.5

Compound 4.5 Empirical formula C16 H15 B F2 N O2 S Formula weight 334.16 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P21/n a = 9.6836(7) Å α = 90° Unit cell dimensions b = 5.6340(4) Å β = 96.073(2)° c = 27.2833(19) Å γ = 90° 3 Volume 1480.15(18) Å Z 4 Density (calculated) 1.500Mg/m3 Absorption coefficient 0.249 mm-1 F(000) 692 Crystal size 0.187x 0.138 x 0.101 mm3 Theta range for data 1.501 to 25.224° collection Index ranges -11<=h<=11, -6<=k<=6, -32<=l<=32 Reflections collected 17125 Independent reflections 2661 [R(int) = 0.0516] Completeness to theta 99.2 % Absorption correction SADABS Max. and min. 0.7527 and 0.6571 transmission Refinement method Full-matrix least-squares on F2 Data / restraints / 2661 / 0 / 210 parameters Goodness-of-fit on F2 0.996 Final R indices [I>2sigma(I)] R1 = 0.0402, wR2 = 0.1235 R indices (all data) R1 = 0.0451, wR2 = 0.1295 Largest diff. peak and hole 0.427 and -0.321 e.Å-3

120

Results and Discussion

The first work on dimeric BF2 compounds began more than four decades ago with the work of Umland and co-workers.298 In a 1973 report, they presented the first salphen BF2 compound; a 1:1 complex (compound 4.1) was reported by these authors using benzene as the reaction solvent. More recently, a bis-BF2 adduct of a t-butyl modified version of compound 4.1 was presented by Lu and co-workers.310

We were able to synthesize the π expanded analogue of 4.1, compound 4.2, using dichloromethane as the solvent with DIEPA as the base. In addition, we were able to reproduce the synthesis of compound 4.1 and elucidate its structure, as shown in

Figure 4.2. Both compounds exhibit nearly identical geometrical parameters. The

BF2 units are coordinated by bidentate chelates comprised of a hydrazine-Schiff base nitrogen atom and a deprotonated phenolic oxygen atom. Only one equivalent of boron is coordinated by these two ligand systems; the second potentially chelating segment remains unreacted even in the presence of an excess of BF3.

In compound 1, the B-O and B-N bonds measure 1.446(3) Å and 1.620(3) Å respectively. In compound 4.2, which was elucidated at lower resolution than 4.1, the B-O bond measures 1.473(12) Å and the B-N bond is 1.589(12) Å. In both compounds, notably the B-O bonds are measurably shorter than the B-N bonds. The

B-F bonds in both compounds range between ~1.36 and ~1.38 Å. Both compounds are planar; there is no observed rotation along the N-N bond of the azine or the C-C bond pendant to the Schiff base. This is clearly due to the presence of an intramolecular hydrogen bond between the OH and the Schiff base of the unligated portions of the compounds

121

The ortho, meta, and para naphthylphen ligands can be also be readily generated from the corresponding diamines and 2-hydroxynaphthaldehyde using acetic acid as the catalyst. The BF2 chemistry of the ortho and para salphen ligand systems been explored by Jiang, although the structures of these compounds were

309 not elucidated. Lu and co-workers also presented the synthesis of bis-BF2 adducts t-butyl modified forms of the meta and the para salphen.310 We were able to synthesize the bis-BF2 modified π expanded ortho, meta, and para 2- hydroxynaphthaldimine salphen analogues using and excess of BF3 and DIPA

(Scheme 4.1). We structurally characterized each resultant compound (4.3-4.5) by

X-ray methods, which can also be seen in Figure 4.2. As expected, each ligand coordinates the two equivalents of BF2 via a N,O chelate; as in compounds 4.1 and

4.2, the B-O bonds are much shorter (~1.45 Å) than the B-N bonds (~1.58-1.59 Å).

Similarly, the B-F bonds measure ~1.38 Å.

Unlike the mono-BF2 compounds 4.1 and 4.2, the bis adducts are not planar.

Without the hydrogen bond to enforce planarity, these compounds can rotate along the C-C bonds pendant to the phenyl ring. In 4.4 and 4.5, the meta and para compounds respectively, the naphthyl groups deviate ~14.4 and ~30.2° respectively from the planes of the phenyl rings. We surmise that these deviations observed in the solid state result from packing forces and that these rings can rotate freely in solution. In compound 4.3, however, the lack of planarity can be ascribed to the steric bulk of the ortho naphthyl units. The naphthyl rings are at angles to the central phenyl ranging from ~63.1° to ~75.6° for the two equivalents in the solid state, and the phenyl rings are oriented in opposite directions. These compounds can be

122 considered chiral, with both enantiomers present in the solid state. This type of chirality can be considered as a variant of strain induced chirality, similar to that seen in polyarenes or the binap family of ligands.39,40

Figure 4.2: The crystal structures of 4.1-4.5 with 35% thermal ellipsoids. Hydrogen atoms on carbon atom positions have been omitted for clarity We probed the absorption and emission spectra of compounds 4.1-4.5, which are shown in Figures 4.3 and 4.4. Table 4.6 lists the photochemical parameters of

123 these same compounds. All of them exhibit two absorption peaks; one at higher energy below 350 nm, and a second peak at a lower energy depending on the structure of the compound. The azine bridged compound 4.2 shows the most red shifted absorbance, followed by the para (4.5), meta (4.4), and ortho (4.3) phenylene bridged compounds. The extinction coefficients for all compounds rise as the absorption maxima shift to lower energies. With regard to emission, compounds 4.1 and 4.2, with heteroatoms unoccupied by BF2 coordination, exhibit the lowest quantum yields of emission.

Figure 4.3: Normalized absorption (solid line) and emission (dotted line) spectra of 4.1 and 4.2 in acetonitrile. Compounds were excited at the lowest energy maxima for emission spectra.

124

Figure 4.3: Normalized absorption (solid line) and emission (dotted line) spectra of 4.3-4.5 in acetonitrile. Compounds were excited at the lowest energy maxima for emission spectra.

Table 4.6: Selected absorption and emission parameters for compounds 4.1-4.5.

Compound λmax(nm) ɛ λex λem(nm) Q.Y. Stokes shift (M−1⋅cm−1) (nm) (%) (nm) 4.1 358 2.1 x 104 358 570 <1 212 4.2 432 3.8x 104 368 574 1 206 4.3 338 2.5x104 338 452 6 114 4.4 400 2.9x 104 400 462 6 62 4.5 411 3.5x104 411 499 26 88

In order to gain greater insight into the electronic structures of these π expanded BF2 compounds, we carried out DFT and TDDFT calculations to determine their orbital compositions and energies as well as to predict their spectra

Figure 4.5 shows the relative energy levels for the compounds investigated in this

125 report. For compounds 4.1 and 4.2, the hydrazine bridged compounds, the HOMO and LUMO orbitals are relatively isolated. The HOMO-LUMO gap shrinks from

~2.60 to ~2.53 eV from 4.1 to 4.2, in agreement with the absorption trends. For 4.3-

4.5, the HOMO and HOMO-1 as well as the LUMO and LUMO+1 are closely spaced; in 4.3 and 4.4 they are nearly degenerate. The HOMO-LUMO gaps decrease as one proceeds from 4.3-4.5 (~3.06, ~3.10 and ~2.78 eV), which also correlates to the sequential bathochromic shifts in these compounds

Figure 4.5: DFT predicted (TPSSh functional / 6-311G(d) basis set) frontier orbital energy levels for 4.1-4.5. The structures of the frontier orbitals of 4.1 and 4.2 are shown in Figure 4.6. Both the HOMO and LUMO are π bond in character, and extend across the azine link due to the planar nature of the structures of 4.1 and4. 2. This in part explains the clear red-shift in absorption of compound 4.2 relative to 4.3-4.5. Figure 4.6 displays the

HOMO-1, HOMO, LUMO and LUMO +1 for 4.3-4.5. In compounds 4.3 and 4.4,

126 all four of the orbitals are primarily naphthylaldimine based, with some bridging phenylene character in all four orbitals. In contrast, the para substituted phenylene compound 5 has significant phenylene character to the HOMO and LUMO, and much less in the LUMO+1 and HOMO-1. In general, the degree of phenylene participation in the frontier orbitals along with the ability to form a planar configuration both clearly correlate with the increase in red shift of absorption and emission for 4.3-4.5. We carried out TDDFT investigations into 4.1-4.5, and the experimental versus predicted spectra for these compounds can be seen in Figure

4.7. Overall, we observe good agreement between theory and experiment for all of the compounds. In the hydrazine bridged compounds, the bands arise from what can be characterized as π to π* transitions. In compound 4.1, this is a HOMO-2 to

LUMO transition, while in 4.2 it is a HOMO to LUMO transition. The expansion of the π system in 4.2 destabilizes the ground state π orbital as well as stabilizes the

LUMO, resulting in a very significant red shift in the primary absorption band. In compounds 4.3-4.5, the primary absorption bands can also be described as π to π* transitions, with the electron moving from an orbital with more naphthylaldimine character to one with a higher percentage of phenylene bridge composition.

However, due to the lack of planarity in 4.3-4.5, we do not observe the similar degree of orbital stabilization/destabilization as seen in 4.2.

127

Figure 4.6: DFT predicted frontier orbital structures for 4.1-4.5.

128

Figure 4.7: Observed and calculated Uv-visible spectra for 4.1-4.5.

Conclusion

In conclusion, we have prepared a series of π-expanded azine and salphen BF2 fluorophores. The hydrazine bridged system 4.2 incorporates only one equivalent of boron, similar to that seen for the previously synthesized compound 4.1. The phenylene-bridged compounds all incorporate two equivalents of BF2. The quantum yields of emission range from very low (<1%) to ~25% for the para substituted compound 4.5. Our future work on these compounds will investigate their time resolved photophysical behaviour.

129

CHAPTERV

SUMMARY

Although template reactions of 1,3-diiminoisoindoline (DII) with transition metal ions, lanthanide cations, and cations of boron and calcium have been known for over 50 years, the reaction products have been limited to phthalocyanines, superphthalocyanines, subphthalocyanines, and hemiporphyrazines. The use of a templating agent to prevent ring closure in reactions with DII was previously unreported. Simple one –pot synthetic method resulted in the template formation of both rhenium and boron based aza(dibenzo)dipyrromethenes.

In Chapter II, the use of Re(CO)5Cl to template the formation of aza(dibenzo)dipyrromethenes was described. When water was present during the reaction, hydrolysis of the product occurred, resulting in the formation of the mixed imino/oxo and bis(oxo) products in addition to the bis(imino) compounds. As the identity of the terminal atoms are changed from NN (bis(imino)) to OO (bis(oxo)), the MLCT band is red shifted by approximately 100 nm, signaling a stabilization in the HOMO orbitals. The proposed theory of stabilization of the HOMO is supported by the cyclic voltammetry results, where

130 the reduction potential becomes more negative as the oxygen content of the terminal atoms is increased.

Similar to the chemistry seen in Chapter II, Chapter III presented a one pot method for the template synthesis of aza(dibenzopyrro)methane using either phenylboronic acid or triphenylborane. In shifting from the bis(imine) to the bis(oxo) terminal groups, there is a bathochromic shift of ~20 nm in the UV-visible and ~10 nm in the emission spectra. DFT and TDDFT calculations were carried out on the complexes. Going form the bis (imino) to the mixed imino/oxo to the bis (oxo) terminus, there is a trend of stabilization of the

LUMO as the oxygen content is increased.

In future, the template synthesis of aza(dibenzo)dipyrromethenes could be extended to other metal ions by using non-labile ligands in positions that would force a planar bidentate binding of the ADBM and prevent formation of phthalocyanine. In addition to extending this chemistry to other metal ions, demetallation of the ligand followed by reacting with phthalonitrile or diamines could potentially form AAB subphthalocyanines or AABB phthalocyanines and hemiporphyrazines.

Chapter IV presented the structure and electronic properties of boron π expanded azine and salphen complexes. While the salpen ligands formed a 2:1 BF2: ligand complex, the azine formed a 1:1 BF2: ligand adduct. In the solid state, the azine complexes are planar due to an intramolecular hydrogen bond while the salphen complexes are non-planar due to the lack of an intramolecular hydrogen bond. The absorbance and emission spectra were studied and it was found that all compounds have large Stokes shifts ranging from 88-212 nm with quantum yields of emission for the complexes ranging from low to moderate.

131

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162

APPENDICIES

163

APPENDIX A

SOLVATOCHROISM OF COMPOUNDS 2.2-2.7.

164

Figure A1: Solvent polarity index (P’) versus λmax for 2.2.

Figure A2: Solvent polarity index (P’) versus λmax for 2.3.

165

Figure A3: Solvent polarity index (P’) versus λmax for 2.4.

Figure A4: Solvent polarity index (P’) versus λmax for 2.5.

166

Figure A5: Solvent polarity index (P’) versus λmax for 2.6.

Figure A6: Solvent polarity index (P’) versus λmax for 2.7.

167

APPENDIX B

PERMISSIONS

168

169

170

171

172

173

174

175

176

177

178