Structures, properties, and applications of soluble polyazulene and azulene containing copolymers 1

References 47 Chapter 2 The First Aptly Characterized 1,3-polyazulene: true polyazulene and its ethynylene derivatives for steric hindrance release 57 Introduction 57 Results and Discuss

STRUCTURES, PROPERTIES, AND APPLICATIONS OF

SOLUBLE POLYAZULENE AND

DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE

2003

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In addition, I wish to express my heartful thanks to all graduate students in my research lab

In particular, I would like to than Dr Xu J W., Ms Wang W L., Ms Lin Y., Ms Zhou C Z., Ms Lu H F Mr Wang J H for their advice and friendship

Thanks also go to Ms Tan G K of the X-ray Diffraction Lab of Department of Chemistry for her assistance in analysis of the single crystal structures, all staff of Central Instrumental Lab, Thermal Analysis Lab, Honors Lab, and Chemical Store for their help

I dedicate this project of work to my girl friend who has provided me with so much support and encouragement, just when I needed them most

Last but not least, I would like to express my gratitude to the National University of Singapore for the award of research scholarship and for providing me with the opportunity to carry out the research work reported in this thesis

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Content

Acknowledgements ii

Content iii

Summary xi

Glossary of Symbols xix

Glossary of Abbreviations xxi

List of publications xxiii

Table of the prepared compounds and polymers xxiv

Chapter 1 introduction 1

1 Conducting polymers 1

1.1 The conductivities of conjugated polymers 2

1.2 Mechanism of Polymer Conductivity 4

1.3 Electrical Conductivity Measurement 11

2 Conjugated polymers band gap engineering 12

2.1 Band-gap of conjugated polymers 12

2.2 Reduction of band gap conjugated polymers 13

2.2.1 Minimization of bond-length alternation 14

2.2.2 Reduction of band gap by donor-acceptor systems 16

3 Advanced materials based on π-conjugated polymer 19

3.1 Chromic effect conjugated polymers 20

3.2 Conjugated polymes-inorganic hybrids 22

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4 Azulene and Polyazulenes 26

4.1 Unique structure and interesting properties of azulene 27

4.2 Recent application of azulene and its derivatives in materials science 29

4.3 The polyazulenes (PAZs) 31

5 Oligomers Approach 34

5.1 Monomers and Oligomers: model compound for understanding of polymer properties 36

5.1.1 Structure/property relationships 36

5.1.2 The doping mechanism revealed from the oligomers approach 39

5.1.3 The crystal structure of oligomers 41

5.2 Monomers and Oligomers – New approach for advanced materials 43

• Molecular electronic 43

• FET 44

• Optical application 45

6 Project objective 45

7 References 47

Chapter 2 The First Aptly Characterized 1,3-polyazulene: true polyazulene and its ethynylene derivatives for steric hindrance release 57

Introduction 57

Results and Discussion 59

Synthesis of polyazulene 59

Synthesis of poly(azulene-ethynylene) and poly(azulene-ethynylene-thienyl) 60 Thermal Analysis 61

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Solubility Test 62

1HNMR Characterization 64

FT-IR spectrum 65

Electronic Spectra 67

EPR Measurement 70

Conductivities Mesurement 74

XRD and morphology study 75

Cyclic voltammogram 77

Conclusions 78

References 80

Chapter 3 Stimuli-Responsive Conjugated Copolymers Having Electro-Active Azulene Units in the Main Chain 81

Introduction 81

Results and Discussion 83

Monomer Synthesis and Characterization 83

Monomers characterization 84

UV-vis Spectra and EPR studies 87

Polymers synthesis and characterization 89

Gel properties study 94

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Thermal analysis 96

UV-vis and UV-vis-NIR Spectroscopic Study 99

EPR studies 102

XRD analysis 105

Morphology of the neutral and doped copolymers 106

Electrochemical Analysis 107

Electrochemical Impedance Spectroscopy study 110

Electrical Conductivity 112

Conclusions 113

References 115

Chapter 4 Crystal Structures of Monomers and Oligomers Containing Azulene Unit – Model Compounds for the Corresponding Polymers 119

Introduction 119

Results and Discussion 120

Model compounds design and synthesis 120

Characterization 122

Structural Analysis 126

Structure of Monoa and Monob 126

Structure of Oligoa and Oligob 131

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Structure of MonoO6 138

UV-vis Spectra and NMR studies 140

Cyclic voltammogram study 146

Conclusions 149

References 152

Chapter 5 Reason for the high conductivity of the azulene containing copolymers by studying their monomer-TCNQ charge-transfer crystal structures and corresponding polymers-TCNQ charge-transfer complex 154

Introduction 154

Results and Discussion 157

Synthesis of the monomers and their charge-transfer complex 157

Characterization 159

Single-crystal structure analysis 161

Crystal structure of Monoa.TNB 161

Crystal structure of Monoc.TCNQ 166

UV-vis spectrum of the complex 172

Post-synthesis and characterization charge-transfer complex of conjugated polymers and TCNQ 175

Electronic Spectrum and EPR study 179

Conductivity measurement of the CT complex 181

Conclusions 181

References 184

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Chapter 6 Coordination of Multinuclear Transitional Metal

Tunable Hybrids 186

Introduction 186

Results and Discussion 189

Model Compounds Synthesis and Characterization 189

Model compound synthesis 189

Structural Characterization 190

Solid-state crystal structure of model compounds 193

UV/vis spectra and MLCT effect in the model compounds 198

Synthesis of hybrids of polymer and ruthenium carbonyl cluster 200

The chromium of ruthenium carbonyl cluster coordination to the polymers revealed by HNMR and FT-IR 202

Morphologies Studies 205

Thermal Properties 207

Optical and electronic properties studies 209

Electrical chemistry study 211

Sensitivities of the hybrids to iodine and TFA 213

Conclusions 216

References 218

Chapter 7 Novel polyradicals stabilized by the vertical and horizontal delocalization of the electrons 220

Introduction 220

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Results and Discussion 223

Monomer synthesis and characterization of the cation radical 223

Polymers synthesis and characterization 227

Thermal properties 229

Electrochemical Properties 230

Electronic spectroscopy study 231

EPR spectroscopy study 234

Conclusions 236

References 237

Chapter 8 Conjugation control by changing the main backbone conjugation type or by side aromatic substituent 239

Introduction 239

Molecular design 242

Results and discussion 243

Part 1 Conjugation control by changing the main backbone conjugation type 243

Model compounds synthesis and characterization 243

Structure analysis of the model compounds 248

Polymers synthesis and characterization 252

Optical properties 255

Part 2 Conjugation control by side aromatic substituents 257

Model compounds synthesis and characterization 257

Structural analysis 260

UV-vis spectra study 263

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Electrochemical properties 265

Synthesis and characterization of conjugated polymers bearing phenyl pendant group 267

UV-vis and CV studies 270

Conclusions 272

References 275

Chapter 9 Experiment Section 277

Materials 277

Solvents 277

Chemicals 277

Instrumentation 278

Synthesis 281

Synthesis of main compounds monomers 281

Synthesis of polymers 311

Chapter 10 Conclusions and Suggestions for future work 320

Conclusions 320

Suggestions 323

Appendix 324

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Summary

A series of azulene-based conjugated polymers and their model compounds have been synthesized and their interesting properties reported These novel materials feature many interesting properties, such as the chromic effect upon protonation, high conductivity upon doping, formation of the charge-transfer complex with electron-acceptor, coordination with transitional metal complex, and the formation of stable polyradicals These advanced materials offer technologically useful applications in, for example, electrochromic devices, molecular electronics, catalysis, and anti-oxidants Furthermore,

to gain insight into the relationship between the structure and properties of these conjugated polymers, corresponding model compounds were synthesized and their single crystals were prepared Results reveal that these are ideal model compounds for investigating the structure-properties relationship, doping mechanism, and the coordination mode of the formation of hybrids

The focus of this work has been to develop novel materials by inserting the intact azulene into the polymer backbone This is attractive because of the special optical and electrical properties of azulene As a non-alternated 10-π electron aromatic system with pronounced polarizability and a tendency to form stabilized radical cations as well as anions, azulene should be predestinated to be a building block for the construction of new materials with interesting chemical and physical properties However, up to now, only polyazulene has been prepared without detailed characterization because of its insolubility The reported HNMR spectrum for polyazulene indicates destruction of the unique structure of azulene Thus, in Chapter 2, we show the preparation of a truly

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soluble 1,3-polyazulene by dehalogenative polycondensation of 1,3-dibromoazulene, using an organonickel catalyst Furthermore, 1,3-polyazulene was characterized by

1HNMR spectroscopy, IR, and elemental analysis, which shows that azulene still kept its unique structure in the polymer backbone Most interestingly, the polymer exhibits high conductivity and paramagnetic properties upon protonation

To increase the process-ability of azulene-containing polymers and to develop novel materials, copolymers containing azulene moiety and 3-aklyl-thiohene were prepared and investigated (Chapter 3) The resulting copolymers showed high thermal stability in air and good solubility in most organic solvents Interestingly, chromic effect upon protonation and reversible protonation-deprotonation (P-DP) processes was observed via UV-vis and UV-vis-NIR spectroscopy in solution and at solid state This indicates the potential application of these copolymers in sensors Moreover, the sensitivity of these copolymers to the external stimuli was also investigated in detail by EPR experiments and conductivities measurements Especially within the EPR experiments, nitrogen-oxygen permeation tests showed the radical content decreased in the presence of O2, and recovered when vented with N2, indicating that these copolymers can be used as anti-oxidants These copolymers can be rendered conducting (1-100 S/cm) through two independent routes: doping with iodine or protonation with trifluoroacetic acid (TFA) The SEM studies on morphology revealed the formation of nano-scale doping centres in the iodine doped sample and formation of conductive channel in the TFA protonated sample, which may be have contributed to the high conductivity of the copolymers Doping and protonation mechanisms were further investigated by cyclic voltammetry (CV), EPR, and electrochemical impedance spectroscopy (EIS) The stable doping state

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and mechanism differences between TFA protonation and iodine doping were observed during these experiments

To better understand the relationship between the structure and properties of these copolymers, five model compounds were synthesized by Grignard coupling or Stille coupling, and their crystals were prepared These compounds were characterized by NMR, FT-IR and 2-D NMR techniques Their single crystal structures showed that a large torsion angle existed between the azulene ring and the thiophene ring in these model compounds In general, this explains the amorphous structure of the resulting copolymers and the identification of the UV-vis spectra of these copolymers in solution and at solid state The investigation of the UV-vis spectra, EPR and 1HNMR of the protonated model compounds revealed the formation of the azulenium cations during protonation Cyclic voltammetry experiments revealed cation formation in the monomers and dication formation in these oligomers

Yet, a question arises when comparing the results in Chapter 3 and Chapter 4 In Chapter

3, our copolymers showed high conductivity upon doping, often observed in the coplanar conjugated polymers, while we found a large torsion angle (> 350) between the azulene ring and the thiophene ring in these model compounds (Chapter 4) Thus, we must answer why these conjugated polymers with large torsion angle show high conductivity

To answer this question, a series of charge transfer (CT) model compounds that mimic the doping process were synthesized and their single crystals were prepared (Chapter 5)

An important feature of these charge-transfer crystals is the rotation of one thiophene ring before and after “doping” Single crystal analysis of these CT complex structures showed that after formation of the CT complex, one thiophene ring rotated to the plane of the azulene ring That is, one torsion angle between the azulene ring and thiophene ring

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greatly decreased (<100) Also, the UV-vis spectra experiments showed the charge transfer between the monomers and electron-acceptors, such as TCNQ and TNB Based

on these observation, a novel charge-transfer complex between the conjugated polymers and electron-acceptors, such as TCNQ, were prepared These CT polymers were characterized and confirmed by HNMR, FT-IR, UV-vis spectra and EPR HNMR spectra and thermal analysis confirm the formation of the CT complex and calculated the ratio between TCNQ and conjugated donor polymers The UV-vis spectra and EPR experiment confirmed the charge-transfer interaction between TCNQ and the π-conjugated polymers

To further develop the CT complex, based on the conjugated polymers, we carried out design and synthesis of a metal-ligands charge-transfer (MLCT) complex between these copolymers and ruthenium carbonyl cluster Novel organometallic conjugated polymers with multinuclear ruthenium clusters were prepared (Chapter 6) by means of refluxing the conjugated polymers with Ru3(CO)12 in xylene The chromium, within the ruthenium carbonyl cluster coordination on the azulene, controls the electronic and optical properties of the resulting hybrids, as revealed by HNMR spectrum, UV-vis spectrum analysis and CV studies This post coordination process offers a flexible and straightforward route to organometallic polymers that have any desired composition, and thus, tunable optical and electronic properties Furthermore, this is also the first example

of transitional metal cluster attachment onto a conjugated polymers support The morphologies, found with SEM, reveal an increase in surface area of the resulting hybrids

via formation a sphere structure, greatly increasing the catalyst contact area. Quartz crystal microbalance (QCM) measurements also displayed the difference in sensitivity of our hybrids to iodine vapour from that of metal free polymers To better understand the

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