Investigations of the Electronic Structure and Excited State Processes of Transition Metal Complexes with Polypyridyl and Schiff Base Ligands

UNIVERSITY OF CINCINNATI Date:___________________ I, _________________________________________________________, hereby submit this work as part of the requirements for the degree of: in: It is entitled: This work and its defense approved by: Chair: _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ Investigations of the Electronic Structure and Excited State Processes of Transition Metal Complexes with Polypyridyl and Schiff Base Ligands A dissertation submitted to the Division of Research and Advanced Studies of the University of Cincinnati in partial fulfillment of the requirements for the degree of DOCTORATE OF PHILOSOPHY (Ph.D.) In the Department of Chemistry of the College of Arts and Sciences 2005 by Pamilla J. Ball B.S., University of Cincinnati, 2000 Committee Chair: Dr. William B. Connick Acknowledgements Nearly a decade ago when I stepped onto this campus, the last thing I thought I would be leaving with is a Ph.D in chemistry. I surely would have told you that I wasn’t smart enough to do that. Without a doubt, I am where I am because of the many wonderful people who have come into my life. Foremost, I have to thank my advisor Dr. Bill Connick. His passion, focus, creativity, and brilliance have made a lasting impression on my life. I am grateful for all the things he has taught me not only about science but about life and for the person he has helped me to be. By example he has taught me to never accept less than perfection, to question everything, and not to half-ass anything. I am grateful that he did not let me slink away and that he did not make this road straight, flat and comfortable. That he always challenged us to take things one step further and to think about things in a different light. I am grateful for all his encouragement, concern and advice along the way and for his uncanny ability to have just the right thing to say at just the right time. I am also especially grateful to Drs. Baldwin and Ault for their willingness to guide me along in this process as well. And who knew that so many cool people hang out in the chemistry lab. Day in and day out, its their support, advice, perspective, and knowledge that has made all the difference. Thanks to Hershel and Wendi for being the first ones and setting the standards high. To Tyler for his guidance, friendship, advice, wisdom, technological support, impromptu song lyrics, making fun of everyone else, and for having no idea what I am talking about. To Stuart for his friendship, for keeping me laughing with the gophers and ligers, and for always knowing what I am thinking. To Levi for challenging me, for his criticism, and for his friendship. To Justin for his intellectual curiosity and useless information. To Dev for all his ideas, knowledge and laughter…but not for his tuna in the microwave. To Seher for her peacefulness and to Amber for being such a great person to pass the quenching off to. To the undergrads Aaron, Neal, and Katye for their significant contributions to this research. To Greg for his friendship and the GBV addiction. And saving the best for last -to my special superstar sidekick, Jenny -for the code language, the large sports bras, the late nights, long talks, her style, her encouragement, for keeping me going, for helping me see things a little differently and for always telling me that I was the greatest. And to so many other members of the chemistry department… Nathan ,Alison, Beth and Sara for all your help and advice. Jean for always understanding and helping me keep things in perspective with the scale of life. Chris G. for calling me Pammy J. Some of those who were there at the beginning- Rachel Z. and Mike for influencing me more than you realize. For good friends, especially Jill and Michelle. Most importantly, to mom and dad, my two best friends, who know the least about chemistry but somehow figured out how to run this marathon with me. Abstract A detailed study of the emission and photophysics of late transition metal complexes as well as investigations of the role of π-stacks in mediating electronic communication have been undertaken as a step towards the design of systems that will undergo photoinduced two electron transfer. Here we report investigations of the self- quenching and energy-transfer reactivity of a novel luminescent platinum(II) diimine complex, Pt(tmphen)(bdt) (tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline, bdt=1,2- benzenedithiolate), using both time-resolved and steady-state emission spectroscopies. By simulating data according to analytical solutions derived for the lifetime and quantum yield, we have shown that the self-quenching reactivity can be described by the same model that is used to describe excimer formation in organic aromatic systems. In addition we have mapped out a narrow range of values for the kinetic parameters that describe self-quenching. We have also prepared binuclear rhenium and ruthenium complexes with bridging [2.2]paracyclophane diimine ligands as a means of probing the role of π−stacks in facilitating electronic communication. From spectroscopic data and comproportionation constants we find relatively weak interactions mediated by the paracyclophane bridging group. To better understand the triplet excited states associated with the 2-pyridinecarboxaldimine (R-pyCa) Schiff base diimine ligands we have investigated the electronic structure of zinc(II) chloride complexes prepared with the R- pyCa ligands. Table of Contents List of Figures IV List of Schemes VII List of Tables VIII Chapter 1 Introduction I. Overview 1 II. Platinum(II) Diimine Complexes 3 III. Metal Dimers with [2.2]Paracyclophane Ligands 6 References 10 Chapter 2 Self-Quenching Reactivity of an Excited Platinum(II) Diimine Dithiolate Chromophore I. Introduction 14 II. Results and Discussion A. Characterization 17 B. Concentration Dependence of Emission Lifetimes 23 C. Self-Quenching 26 D. Concentration Dependence of Quantum Yield 28 E. Comparison of Stern-Volmer Constants 30 F. Data Modeling 34 G. Comparison of Models 40 III. Conclusions 42 IV. Experimental A. Synthesis 44 B. General Procedures 44 C. Crystal Structure Determination 45 D. Time-Resolved Emission Measurements 45 I E. Steady-State Emission Measurements 46 F. Simulations of Time-Resolved Data 48 G. Simulations of Steady-State Data 50 H. Evaluation of Kinetic Parameters 51 I. Static Quenching Modeling 53 References 55 Chapter 3 Energy-Transfer Reactivity of Pt(tmphen)(bdt) I. Introduction 60 II. Experimental 62 III. Results and Discussion A. Time-Resolved Measurements 65 B. Steady-State Measurements 68 C. Energy-Transfer Kinetics 77 References 81 Chapter 4 Binuclear Metal Complexes with Bridging [2.2]Paracyclophane Ligands: Probing Electronic Coupling Through π-π Interactions I. Introduction 83 II. Experimental 85 III. Results and Discussion A. Synthesis 94 B. Crystal Structures 99 C. NMR Spectroscopy 101 D. Electronic Structures 106 E. Electronic Coupling 110 References 128 II Chapter 5 Preparation and Spectroscopic Investigations of Zinc(II) Diimine Complexes: Probing the Ligand Excited States of R-pyCa Ligands I. Introduction 143 II. Experimental A. Materials 145 B. Measurements 146 C. Preparation of Compounds 148 III. Results and Discussion 151 IV. Conclusions 167 References 169 III List of Figures Figure 2.1. 1H NMR spectrum of Pt(tmphen)(bdt) in d6-dmso 18 Figure 2.2. ORTEP diagram with 50% probability ellipsoids of 18 Pt(tmphen)(bdt) Figure 2.3. Room-temperature absorption and emission and 77 K 21 emission spectra Figure 2.4. Cyclic voltammogram of Pt(tmphen)(bdt) in CH2Cl2 22 Figure 2.5. Cyclic Voltammogram of Pt(tmphen)(bdt) in DMF 23 Figure 2.6. Emission intensity decay profiles of Pt(tmphen)(bdt) 24 Figure 2.7. Plot of k' vs. [Pt(tmphen)(bdt)] 25 1 Figure 2.8. Plot of vs. [Pt(tmphen)(bdt)] 29 Φ ' k' Φi Figure 2.9. Plot of and vs. [Pt(tmphen)(bdt)] 31 ki Φ' Figure 2.10. Plot of Φi/Φ' vs [Pt(tmphen)(bdt)] 33 Figure 2.11. Plot of Effective Absorbance (A526) vs [Pt(tmphen)(bdt)]. 34 Figure 2.12. Plot of the allowed parameter space for data modeled 36 according to Scheme 2.1 Figure 2.13. (a) Experimental and (b) simulated emission decay profiles 38 k' Φi Figure 2.14. Plot of experimental and simulated and 39 ki Φ' vs. [Pt(tmphen)(bdt)] Figure 3.1. Plot of the time-resolved quenching rate as a function of 69 the driving force, ∆G Figure 3.2. Stern-Volmer analyses for quenching of Pt(tmphen)(bdt) 70 with anthracenyl derivatives Figure 3.3. Stern-Volmer analyses for quenching of Pt(tmphen)(bdt) 73 with perylene Figure 3.4. Stern-Volmer analyses for quenching of Pt(tmphen)(bdt) 74 with anthracene in air IV ss Figure 3.5. Plot of the reciprocal steady-state slope K sv as a function 77 of [Pt] for the quenching of Pt(tmphen)(bdt) with anthracene. Figure 4.1 ORTEP diagram with 50% probability ellipsoids showing 114 the geometry of 4,16-bis(benzophenone-imine) [2.2]paracyclophane. Figure 4.2 ORTEP diagram with 50% probability ellipsoids showing 115 the geometry of 4,16-bis(picolinaldimine)-[2.2]paracyclophane (BPPc) Figure 4.3 ORTEP diagram with 50% probability ellipsoids showing 115 the geometry of PBP. 1 Figure 4.4 H NMR spectrum of 4,16-bis(benzophenone-imine) 116 [2.2]paracyclophane in CDCl3 1 Figure 4.5 H NMR spectrum of 4,16-Diamino-[2.2]paracyclophane 116 in CDCl3 Figure 4.6 σp vs. δm for pseudo-para substituted paracyclophanes 117 1 Figure 4.7 H NMR spectrum of 4,16-bis(picolinaldimine)- 117 [2.2]paracyclophane(BPPc) in CDCl3 1 Figure 4.8

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