SYNTHESIS AND FINE-TUNING THE EMISSION PROPERTIES OF NEW AMPHIPHILIC CONJUGATED POLYMERS CHINNAPPAN BASKAR NATIONAL UNIVERSITY OF SINGAPORE 2004 SYNTHESIS AND FINE-TUNING THE EMISSION PROPERTIES OF NEW AMPHIPHILIC CONJUGATED POLYMERS CHINNAPPAN BASKAR (M.Sc., IIT MADRAS) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2004 Dedicated to my beloved parents i Dedicated to my beloved teachers and inspirational minds “If I have been able to see further, it was only because I stood on the shoulders of giants.” - Sir Isaac Newton (1642-1727) ii Acknowledgements Life on Earth is a journey, starts as well as ends with Almighty, like cyclic reactions. During this journey, we are blessed with invaluable teachers and well wishers. It is very difficult to forget important events, ups and downs, achievements, excellent collaborators, contributors, great inspirational minds, and the land of harvest. At the end of my journey to PhD, it is a great pleasure to acknowledge people, who have supported my growth. First and above all I would like to thank Dr. Suresh Valiyaveettil for his invaluable guidance throughout my PhD research work. I thank Prof Lai Yee Hing and Prof Leslie Harrison for their interest in serving on my advisory committee. I would like to thank Prof Jagadese J. Vittal, Prof Chuah Gaik Khuan, Dr. John Yip and Dr. Yang Daiwen for their support as my thesis committee. My heartfelt thanks to Prof Hardy Chan (Vice Dean, Faculty of Science), Prof Andrew Wee (Vice Dean), Prof Xu Guo Qin (Vice Dean), Prof Tan Eng Chye (Dean), Prof Lai Choy Heng and Prof Andy Hor for their support and encouragement during my contributions in Science Graduate Committee (SGC), Graduate Students Society (GSS), and Chemistry Graduate Club (CGC). My special thanks to Prof Hian Kee Lee (Head, Chemistry), Prof Ng Siu Choon (Deputy Head) and Prof Leung Pak Hing (Deputy Head). iii My sincere gratitude to Prof Seeram Ramakrishna (Dean, Faculty of Engineering), Prof Senthil Kumar (Assitant Dean, FoE), Prof Goh Suat Hong (Chemistry), Prof Ji Wei (Physics), Prof Perera Conrad (Chemistry), Prof B. V. R. Chowdari (Physics), Prof G. V. Subba Rao (Physics), Prof K. Swaminathan (DBS) and Dr. Ignacio Segarra (S*Bio). During this period of my doctoral research program, I was certainly blessed to meet many great minds including Prof Roald Hoffmann (1981 Nobel Laureate in Chemistry), Prof Carl Djerassi (Stanford University, USA), Prof C. N. R. Rao (President, JNCAR, Bangalore), Prof Alan Heeger (2000 Nobel Laureate in Chemistry), Prof Hideki Shirakawa (2000 Nobel Laureate in Chemistry), Prof John C. Warner (University of Massachusetts Boston, USA), Dr. Paul Anastas (Director, Green Chemistry Institute, American Chemical Society, USA), Dr. Dennis Hjeresen (Former Director, Green Chemistry Institute, American Chemical Society, USA) and Dr. Mary Kirchhoff (Assistant Director, Green Chemistry Institute, American Chemical Society, USA). My sincerest thanks to all of them for their suggestion, motivation and inspiration. My thanks are also to Prof K. V. Ramanujachary (Rowan University, USA), Prof R. K. Sharma (University of Delhi, India), Prof B. Viswanathan (IIT Madras), and Prof G. Sundararajan (IIT Madras) for their informal discussion and encouragements during their journey in Singapore. I would like to thank Prof Bengt Nordén (Member, The Royal Swedish Academy of Sciences, Chairman, The Nobel Committee for Chemistry in 2000, Nobel Foundation), iv Ms. Birgitta Sandell (Assistant, The Royal Swedish Academy of Sciences) and Ms. Elin Stenbom (Assistant, The Royal Swedish Academy of Sciences) for their support to include the year 2000 Nobel Prize Presentation in Chemistry in my thesis and regular Nobel Posters. My sincerest thanks also go to Prof M. S. Subramanian (My graduate mentor, IIT Madras) and Prof Xavier Machado (My undergraduate teacher, St. Joseph’s College, Trichy, India) for their invaluable suggestion, motivation and encouragement. I want to thank many people without whom I would not have been able to complete the work presented in this thesis. I want to warmly thank all the support staff of the chemistry department in the main office, NMR, MS, Elemental Analysis, X-ray crystallography facilities, chemical stores, Honors lab, analytical lab, organic lab, and in the glassblowing shops. I would like to acknowledge the Department of Chemistry for their hospitality and encouragement on my graduate study. I wish to thank all of my past and present colleagues of the Dr. Suresh Group. I extend my special thanks to my friends especially Felix Lawrence, Lakshmanan, Skanth, Karen, Nacha, Hendry Elim, Kangueane, Arockiam and Peter, classmates and housemates. v I would like to specially thank my parents, brothers (Doss and Julian), and my uncle Sebastian for all the moral and financial support selflessly provided throughout my career. I would like to thank my sister, Ammu Margaret, who stayed up with me over the phone when I was stressed out, encouraged me when I was down, prayed for me when I didn’t think to pray for myself and believed in me when I didn’t believe in myself. Last but not least, I would like to thank God. “So, whatever you eat or drink, or whatever you do, do everything for the glory of God.” – I Corinthians 10:31 (Holy Bible) CHInNaPPaN BaSKAr May 22, 2004 Saturday vi Table of Contents Dedication i Acknowledgements iii Table of Contents vii Summary xii List of Monomers and Polymers Synthesized in this Thesis xvi List of Figures xxi List of Schemes xxiii List of Tables xxiv Glossary of Abbreviations and Symbols xxv Opening Quotations xxxii Chapter 1 Introduction: The Art and Science of Conjugated Polymers 1 1.1 Prologue 2 1.2 Genesis of Conjugated Polymers 6 1.3 A Case History of Poly(p-phenylene)s PPPs 13 1.4 Pyridine incorporated conjugated polymers 23 1.5 Bipyridine incorporated conjugated polymers 28 vii 1.6 Poly(m-phenylene)s (PMPs) 33 1.7 Aim of the project 37 1.8 References 38 Chapter 2 Amphiphilic Poly(p-phenylene)s 75 2.1 Introduction 76 2.2 Synthesis of polymers 77 2.3 Characterization of polymers 79 2.4 Optical and ionochromic properties of polymers 81 2.5 Conclusions 89 2.6 References 90 Chapter 3 Pyridine Incorporated Amphiphilic 94 Conjugated Polymers 3.1 Introduction 95 3.2 Synthesis of polymers 98 3.3 Characterization of polymers 101 3.4 Optical Properties 103 3.4.1 Influence of hydroxyl groups 103 viii 3.4.2 Comparison of properties of polymers 107 3.4.3 Solvatochromic behavior of polymers 107 3.4.4 Effect of protonation and deprotonation of polymers 110 3.4.5 Influence of base 113 3.4.6 Metal complexation of polymers 115 3.5 Conclusions 117 3.6 References 118 Chapter 4 Bipyridine Incorporated Conjugated 125 Polymers 4.1 Introduction 126 4.2 Synthesis of polymers 129 4.3 Characterization of polymers 132 4.4 Optical properties of polymers 133 4.5 Solvatochromic behavior of polymers 134 4.6 Ionochromic effects of polymers 134 4.7 Conclusions 137 4.8 References 138 ix Chapter 5 Experimental Section 142 5.1 Materials 143 5.2 Measurements 143 5.3 Synthesis of polymers 201a-c 145 5.3.1 2,5-Dibromohydroquinone (203) 145 5.3.2 2,5-Dibromo-4-dodecyloxy phenol (204a) 145 5.3.3 2,5-Dibromo-1-benzyloxy-4-dodecyloxy benzene (205a) 147 5.3.4 1-Benzyloxy-4-dodecyloxyphenyl-2,5-bisboronic acid 148 (206a) 5.3.5 1-Benzyloxy-4-dodecyloxy phenyl-2,5-bis(trimethylene 150 boronate) (207a) 5.3.6 Poly(1-benzyloxy-4-dodecyloxy-p-phenylene) (208a) 151 5.3.7 Poly(1-hydroxy-4-dodecyloxy-p-phenylene) (201a) 152 5.4 Synthesis of polymers 301-306 153 5.4.1 2,5-Dibromo-1, 4-dibenzyloxy benzene (312) 153 5.4.2 1,4-Dibenzyloxy-2,5-bisboronic acid (313) 153 5.4.3 Synthesis of Polymer 304 154 5.4.4 Synthesis of Polymer 301 155 5.4.5 Synthesis of Polymer 305 156 5.4.6 Synthesis of Polymer 302 156 5.5 References 157 x Chapter 6 Conclusions and Suggestions for the 158 future work 6.1 Conclusions 159 6.2 Suggestions for the future work 160 6.2.1 Applications of new amphiphilic conjugated polymers 160 6.2.2 Design of new polymer structures: Evolution of 160 hydroxylated polyphenylenes (HPPs) 162 List of Publications Recent Publications 163 Unpublished Papers 163 International Conference Papers 164 International Conference Presentations 166 National Publications 168 National Presentations 169 Appendix 171 Absorption maxima of non-hydroxyl-containing 172 conjugated polymers TG curves of 301-403 178 xi Summary SYNTHESIS AND FINE-TUNING THE EMISSION PROPERTIES OF NEW AMPHIPHILIC CONJUGATED POLYMERS By Chinnappan Baskar May 2004 Since the discovery of conducting polymers in the late 1970’s, research efforts were focused on synthesis and characterization of novel polymers with π-conjugated backbone due to their interesting optical, electrochemical and conducting properties and possible applications in electroluminescent devices, nonlinear optical materials, lasing materials, solar cells, fuel cells, batteries, photoconductors, field effect transistors, chemical and biosensors, nanoscience and nanotechnology, and biomedical applications. A variety of conjugated polymers have been investigated and reported in literature. Among these polymers, poly(p-phenylene) (PPP) and its derivatives have found considerable interest in blue light-emitting diodes over the last ten years. The present work reports on syntheses and fine-tuning the emission properties of a series of new amphiphilic poly(p-phenylene)s PPPs containing free hydroxyl groups and hydrogen bond acceptor groups such as nitrogen atoms on polymer back bone capable of forming an inter/intra molecular hydrogen bonding. This allows us to planarize the neighboring aromatic rings on the polymer backbone and thereby extending the π-conjugation of the polymer backbone.