DESIGN, SYNTHESIS AND PHOTOPHYSICS OF FLUORESCENCE “TURN-ON” CONJUGATED POLYMER CHEMOSENSORS BY LI-JUAN FAN B.S. Nanjing University, 1994 M.S. Fudan University, 1997 DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate School of Binghamton University State University of New York 2006 UMI Number: 3214759 3214759 2006 UMI Microform Copyright All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, MI 48106-1346 by ProQuest Information and Learning Company. © Copyright by Li-Juan Fan 2006 All Rights Reserved Accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate School of Binghamton University State University of New York 2006 Wayne E. Jones, Jr.___________________________________________ April 27, 2006 Advisor, Chemistry Department Susan L. Bane_______________________________________________ April 27, 2006 Chair, Chemistry Department Alistair J. Lees_______________________________________________ April 27, 2006 Chemistry Department Mark D. Poliks_______________________________________________ April 27, 2006 Chemistry Department Susannah Gal________________________________________________ April 27, 2006 Outside Examiner, Department of Biological Sciences iii ABSTRACT This dissertation explores the synthesis, characterization, and application of conjugated polymers as fluorescence “turn-on” chemosensors. A series of conjugated polymers using the poly[p-(phenyleneethynelene)-alt-(thienylene-ethylene)](PPETE) polymer backbone were prepared using N,N-diethylamino (dea) and N,N,N’- trimethylethylenediamino (tmeda) groups as receptors. The conjugated polymers were designed as fluorescence “turn-on” chemosensors based on a photoinduced electron transfer (PET) mechanism in which the polymer fluorescence is quenched in the absence of coordinating analytes. A chelation-enhanced fluorescence (CHEF) phenomenon results upon coordination of a cation to the redox active receptor as a result of termination of the fluorophore quenching process. The polymers were fully characterizated by NMR, FTIR, Gel Permeation Chromatography (GPC) and elemental analysis. Detailed photophysical studies of dea-PPETE and tmeda-PPETE demonstrated relatively weak emission at λ max = 488 nm with quantum yields of 0.11 and 0.09. Room temperature emission studies show that tmeda-PPETE exhibited a fluorescence “turn-on” response in the presence of many cations at less than 500 nM concentrations. For example, Hg 2+ in aqueous solution causes the fluorescence of tmeda-PPETE to increase by a factor of 2.7 at less than millimolar concentrations. This represents the first example of a conjugated polymer applied as a fluorescence “turn-on” chemosensor based on the PET mechanism. The competitive role of PET and energy migration is critical to sensor function. This was investigated by synthesizing a series of PPETE’s with different amino receptor iv loadings. Theoretical and experimental studies revealed that the limited sensitivity achieved in this system may be attributed to relatively slow energy migration (<10 9 s -1 ) along the polymer backbone relative to the emissive lifetime (∼10 -10 s). A highly selective and sensitive sensory system towards iron cations in solution was achieved by preparing a transition metal derivatized conjugated polymer based on Cu 2+ quenching. By preloading Cu 2+ onto the receptor of tmeda-PPETE, fluorescence enhancements of 150 fold were achieved in the presence of 10 micromolar of iron cations . The combination of the conjugated polymer and metal cation created a selective sensor and offers a new paradigm for further sensor design. v To my family vi ACKNOWLEGMENTS My gratitude begins with my advisor, Dr. Wayne E. Jones, Jr., who gave me the opportunity to explore in this interesting field freely. I appreciate his guidance, encouragement and patience with me through the past several years. His unique way of mentoring student has helped me to come to know how science truly works and like science more than ever before. I have gained more confidence and achieved more independence in doing research under his supervision. I also learned a great deal from him in the way of thinking, solving problems and communicating with others in research and teaching. His insight into science and friendly attitude towards students also made the entire journey very fruitable and enjoyable. I also thank him for his support and understanding in other aspects of life besides research. I would also like to extend my thanks to my committee: Dr. Susan Bane, Dr. Alistair Lees, Dr. Mark Poliks and Dr. Susannah Gal for taking the time to read my dissertation, useful discussion and all other help throughout my graduate study in Binghamton University. Dr Scott Handy should also be thanked for serving as the committee member for my preliminary oral exam. I appreciate Dr. Brendan Flynn and Professor Emeritus, Dr. Stanley K. Madan for devoting their precious time in reading and correcting this dissertation and all my manuscripts before submitting to different journals. I benefited a lot for my writing from Dr. Flynn’s sharp and picky eyes as a teacher in reading my writing. Dr. Mandan’s discussion about coordination chemistry and other aspects of life seems also became a part of my everyday life in the past several years. vii I also thank Dr. Mark Poliks and Dr. Barbara Poliks to be my mentors and also friends during the past several years. I got to know Dr. Mark Poliks in his polymer and NMR class. I was impressed by his excellent teaching skill, broad knowledge and great responsibility towards students. I also thank him for the instruction in the NMR project related to my research. Dr. Barbara Poliks is such a warm-hearted lady and I really enjoyed the discussion with her about many things. I feel very lucky they are always there for me whenever I needed help and the help was always given very timely. I would like to give my special thanks to my dear friends, Dr. Yan Zhang and Dr. Zhengtao Zhu. They brought me here and through them I got to know where Binghamton University was and also the Jones group. I am grateful that they assisted me to settle down, allowed me to be their “dependent” for the first year I was here and for continuous support even after they left. I have so many friends and colleagues in the Chemistry Department that have made this journey enjoyable. First, I wish to thank the whole Jones group, including previous and current members. Dr. Biwang Jiang, who started this conjugated polymer project, came to my poster at ACS meeting in New York City and then became my friend. I was surprised that he still had many good suggestions about my research after so many years away from our group. Dr. Szu-wei (Steve) Yang, who graduated in the first year I joined the group, still was around and willing to provide help whenever I asked for. Dr. Yan Zhang helped me to start the synthesis and Dr. Cliff Murphy helped me to start the photophysics studies. Dr. Dave Sarno helped me to get familiar with the lab during the first summer research. Dr. Cliff Timpson helped me with my E-Chem experiments during his stay here for the sabbatical semester. Special thanks owe to Justin Martin, a really viii smart guy, who was my computer specialist and consultant for the past several years and also brought a lot of laughter to our lab. Thanks also should be given to Dr. Hong Dong to be my Chinese-Speaking partner in the lab. I’d like to thank all other members in our group, namely, Dr. Ed Fey, Fredrick Ochanda, Jasper Chiguma, Wenlong Gui, Sarah Angell, Matt Parker, Kat Minerly and many undergraduate students in our lab. Thank you all for helping me with the research and all other fun we had in the lab besides the research. Some other people outside our group must be thanked for helping with my research. I would like thank Dr. Yanan Zhang for acting as my organic synthesis consultant; Dr. Jürgen Schulte for helping me with the NMR; Dr. Tatini Radhakrishna for helping me with the GPC; Dr. Nikolay Dimitrov for discussion about E-Chem; Dr Robert Ben and Dr. Scott Handy for discussion about some synthesis when they were still in the department; Dr. David Doetschman and Dr. Steve Yang for the EPR experiment and related discussion. Dr. Tom Troxler at the University of Pennsylvania must also be thanked for running all the lifetime experiments for us. Many people in the chemistry department must be thanked for their support besides research, such as Richard Quest, Dr. Bob Kematic, Dr. Alexa Silva, Mary Bridge , Renee Sersen, Pat Gorman, Linda Schaffer, Bob Gonzales, Dat Tran, Daniel Brennan. Elizabeth Brown in the Science Library should also be thanked for her assist in literature searching. I also want to thank all the Chinese people in the Chemistry Department besides I already mentioned above, Namely, Chunmei Ban, Chen Chen, Quan Fan, Dr. Xiaojuan Fan, Li Han, Yan Lin, Shuhuai Liu, Dr. Jin Luo, Dr. Yanning Song, Jie Xiao, Linyan ix [...]... 21 Figure 1-18 Structure of a conjugated polymer showed fluorescence “turnon” upon trysin 22 Figure 1-19 Structure of the two polymer components for fabricating a sensor sandwich 22 Figure 1-20 Structure of a conjugated polymer as fluorescence turn-on chemosensor for anions 23 Figure 2-1 Orbital energy diagram for fluorescence turn-on PET sensors with amino receptor before and after binding cation... of amino receptor loaded phenyl building blocks 137 Scheme 5-2 Unsuccessful synthesis of dea-PPE and tmeda-PPE 139 Scheme 5-3 Synthesis of 2, 5-dibromo-thiophene-3-ylmethylamine 142 Scheme 5-4 Unsuccessful synthesis of a-PPETE 142 Scheme 5-5 Synthesis of phth-PPETE 144 Scheme 5-6 Unsuccessful synthesis of a-PPETE 144 Scheme 5-7 Synthesis of thiourea group loaded thienyl building block 150 xx LIST OF. .. read-out Sometimes a conjugated polymer can act as a combination of two or all three elements with careful molecular design The combination of the sensitivity of fluorescence and unique electronic properties of conjugated polymers provides new opportunities for sensory system development One type of conjugated polymer fluorescent sensor is based on the conformational change of conjugated backbone driven... both in reality and in spirit Finally, this work was funded by the National Institute of Health (Grant No 1R15-ES10601-01) and Research Foundation of the State University of New York at Binghamton x TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SCHEMES LIST OF SYMBOLS AND ABBREVIATIONS Introduction to Fluorescent Chemosensors 1 1.1 Introduction to Sensors 1 1.2 Fluorescent Chemosensors 4... Mechanism of Sonogashira Coupling 41 Scheme 2-2 Polymerization for PAE polymers under Sonoghshira coupling proctol 43 Scheme 2-3 Synthesis of 1,4-diethylnyl-2,5-didodecyloxybenzene 44 Scheme 2-4 Synthesis of receptor-loaded monomer 45 Scheme 2-5 Synthesis of conjugated polymers containing amino receptors 48 Scheme 3-1 The Synthetic Route of (x%-tmeda)-PPETEs with Different Receptor Loading 70 Scheme 5-1 Synthesis. .. Chapter 1 Electronic Energy Transfer 6 1.3 Conjugated Polymer as Fluorescence Chemosensor 8 1.4 Fluorescence “Turn-off” Sensor for Transitional Metals 13 1.5 Fluorescence Turn-on Sensors 15 1.5.1 Small Molecular Turn-on Sensors 15 1.5.2 Examples Polymer Turn-on Sensors 20 1.6 24 1.7 Chapter 2 Dissertation Overview References 27 Synthesis and Characterization of Poly(p-phenyleneethylene)alt-(thienyleneethylene)... 3.3.1 Synthesis and Characterization 70 3.3.2 Polymer Photophysics 75 3.3.3 Photoinuduced Electron Transfer 79 3.3.4 Energy Migration 81 3.3.5 Evaluation of (x%-tmeda)-PPETEs Fluorescence Turn-on Sensors as 85 Ideal polymer system for fluorescence turn-on PET sensors 85 Cation titration 88 3.4 Conclusion 93 3.5 References 94 xii A Highly Selective and Sensitive Inorganic/Organic Hybrid polymer Fluorescence. .. THF upon addition of metal cations 57 Figure 2-12 Emission and UV-Vis spectra of tmeda-PPETE upon addition of different concentration of Hg2+ 59 Figure 3-1 Structures of (x%-tmeda)-PPETEs 66 Figure 3-2 1 73 Figure 3-3 FTIR spectra of (x%-tmeda)-PPETE Figure 3-4 Absorption and emission spectra of (x%-tmeda)-PPETEs THF in 76 Figure 3-5 Quantum yields of fluorescence vs percent loading of amino groups in... Figure 1-8 Basic structures of several fluorescent conjugated polymers 10 Figure 1-9 Structures of several conjugated polymers as fluorescent sensors 11 Figure 1-10 Schematic representation of molecular wire approach to sensory signal amplification 12 Figure 1-11 Structure of PPETE polymers with oligo-pyridine pedants 14 Figure 1-12 Examples of small molecules as fluorescence turn-on sensor with amino... TABLES Table 1-1 Summary of examples of fluorescence chemosensors discussed in Chapter 1 24 Table 2-1 Molecular Weight and Polydispersity of dea-PPETE and tmedaPPETE 53 Table 2-2 Photophysical properties of PPETEs in THF solution at room temperature 54 Table 2-3 Stepwise associate constants between some cations and ligands 58 Table 3-1 Theoretical and Measured Percentages of Nitrogen in (x%-tmeda)PPETE . DESIGN, SYNTHESIS AND PHOTOPHYSICS OF FLUORESCENCE TURN-ON CONJUGATED POLYMER CHEMOSENSORS BY LI-JUAN. Department of Biological Sciences iii ABSTRACT This dissertation explores the synthesis, characterization, and application of conjugated polymers as fluorescence turn-on chemosensors. . the fluorescence of tmeda-PPETE to increase by a factor of 2.7 at less than millimolar concentrations. This represents the first example of a conjugated polymer applied as a fluorescence turn-on