Luận án tiến sĩ: Supramolecular porphyrin-fullerene conjugates: Design, synthesis, electrochemical and photochemical studies

SUPRAMOLECULAR PORPHYRIN-FULLERENE CONJUGATES : DESIGN, SYNTHESIS , ELECTROCHEMICAL AND PHOTOCHEMICAL STUDIES A Dissertation by Suresh Gadde MSc., University of Hyderabad, 2000 Submitted to the Department of Chemistry and the faculty of the Graduate School of Wichita State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy May 2006 UMI Number: 3240344 UMI Microform 3240344 Copyright 2007 by ProQuest Information and Learning Company. 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.

Box 1346 Ann Arbor, MI 48106-1346 SUPRAMOLECULAR PORPHYRIN-FULLERENE CONJUGATES : DESIGN, SYNTHESIS , ELECTROCHEMICAL AND PHOTOCHEMICAL STUDIES I have examined the final copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctorate of Philosophy, with a major in Chemistry ____________________________________ Dr. Francis D’Souza, Committee Chair We have read this thesis and recommend its acceptance: ____________________________________ Dr. Zandler, Committee Member ____________________________________ Dr. Paul Rillema, Committee Member ____________________________________ Dr.

Michael Van Stipdonk, Committee Member ____________________________________ Dr. Rajiv Bagai, Committee Member Accepted for the College of Liberal Arts and Sciences -------------------------------------------------------------------------- Dr. Bischoff, Dean Accepted for Graduate School ------------------------------------------------------------------- Susan Kovar, Dean ii This thesis is dedicated to Ramesh Gadde, Sree Lakshmi Natta, Velikondaiah Bethapudi, and my parents iii ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my research advisor Dr. Francis D’Souza for his support and guidance.

I would also like thank our collaborators: Dr. Osamu Ito, Dr. Michael Van Stipdonk, Dr Wlodzimierz Kutner, Dr. Krzysztof Winkler; Amy McCarty, and their coworkers for their efforts in producing excellent computational, photochemical, electro chemical, mass and X-ray crystal data, which contributed valuable information for the systems studied in this thesis work.

I would like to thank my thesis committee members Dr. Van Stipdonk, Dr. Ram Singhal, and Dr. Rajiv Bagai for their constant encouragement and support.

I would like to thank not only the entire faculty and staff of the chemistry department at Wichita State University but also the University of Hyderabad chemistry department. I would like to thank all the graduate students here at Wichita State University; especially, my lab mates Phil Smith, Lisa Rogers, Amy McCarty, Raghu Chitta, Eranda Maligaspe, Siew-cheng, Kim Tran, Valeriya Karpoviah and Dr. Deviprasad Gollapalli for their support. I would like thank all my friends, mainly Sabita, Ciann, Anne, Michelle, Nagesh, Santosh, and Phani.

I would also like to thank my parents, my sister Lakshmi and brother in-law Johnson. I would like to mention my sincere iv appreciation to my brother Ramesh Gadde, my cousin Sree Lakshmi Natta, and my guru Velikondaiah Bethapudi for their inspiration, constant support, and guidance, without them I would have not made it this far. Finally, I would like to thank the late Dr. Maiya for his significant role in changing my life’s direction.

v ABSTRACT The research reported in this thesis details the synthesis, characterization, electrochemical and photochemical studies of noncovalently linked porphyrin-fullerene based donor-acceptor systems. The first chapter gives an introduction that briefly summarizes the significant events that occur in natural photosynthetic systems, the importance of artificial photosynthetic models and finally, lists new developments in model biomimetic systems of this type. The second chapter discusses synthesis of control compounds and physical methods used in later chapters. The third chapter focuses on the investigation of covalently linked porphyrin-fullerene dyads.

A discussion of the role of axially ligated pyridine in decreasing charge recombination rates can also be found in this chapter. The main investigations in the fourth chapter utilize noncovalently linked porphyrin-fullerene triads with two axial coordination bonds with an emphasis on the importance of structural rigidity and the orientation of the donor- acceptor entities. The fifth chapter discusses the purpose of a secondary donor and the effect it has in charge separation and charge recombination rates for self assembled supramolecular triads formed via ‘two-point’ binding. Noncovalently linked magnesium porphyrin-fullerene dyads and triads are presented in chapter six.

The compounds contained in this thesis were synthesized and characterized by proton NMR and ESI-Mass spectroscopy. Binding constants vi were obtained by using UV-visible, fluorescence and 1H NMR spectral data. DFT calculations were performed to gain insight into the structural aspects and orientation of the donor-acceptor groups in these supramolecular complexes. Electrochemical and emissions studies (i.

steady state and time resolved fluorescence, transient absorption) were employed to obtain free energy changes for electron transfer, lifetimes, charge separation and charge recombination rates for photo - induced electron transfer. vii TABLE OF CONTENTS 1 Introduction 1 1.1 Basic theory of photo -induced electron transfer 2 1.2 PET and EET in biological and non-biological systems 6 1.3 Porphyrins as electron donors and fullerenes as electron acceptors 9 1.4 Covalently linked donor-acceptor systems 12 1.5 Non-covalently linked donor-acceptor systems 17 1.1 Hydrogen bonding modes 18 1.2 Crown ether- ammonium ion binding mode 21 1.3 Rotaxane type of interaction modes 24 1.5 Axial coordination 28 2 Materials and physical methods 32 2.2 Synthesis of control compounds 33 2.4 Summary 40 viii 3 Studies on covalently linked porphyrin-C60 dyads: stabilization of charge separated states by axial coordination 41 3.3 Results and discussion 52 3.4 Summary 82 4 Spectroscopic, electrochemical, computational, and photochemical studies of self-assembled supramolecular triads 84 4.3 Results and discussion 91 4.4 Summary 114 5 Stable supramolecular triads via ‘two-point’ binding invo lving coordination and hydrogen bonding 116 5.3 Results and discussion 127 5.4 Summary 151 ix 6 Spectroscopic, electrochemical, computational, crystallographic and photochemical studies of a self-assembled magnesium porphyrin-fullerene conjugate 153 6.3 Results and discussion 156 6.4 Comparison between intra- and intermolecularly interacting magnesium porphyrin- fullerene dyads 180 6.4 Summary 181 7 Summary 183 Bibliography 189 Appendix 199 x LIST OF TABLES Table …………………………………………………………………………… Page 3.1 Formation constants for axial coordination of pyridine Ligands to Zinc porphyrin- C60 Dyads in o-DCB at 298 K …………………….2 Electrochemical half-wave redox potentials (E1/2 vs. Fc/Fc+) of porphyrin-fulleropyrrolidine dyads in the presence of 0.1 M (n-Bu)4 NClO4 in BN, o-DCB, and pyridine………………………….3 Fluorescence lifetimes (τf ), refractive index of the solvents (η), solvent polarity (ε ), quenching rate -constants (kq P), quenching quantum -yields (Φ qP) via 1MP*, charge-separation rate-constants (kCS C), charge-separation quantum -yields (Φ CSC) and free-energy of charge-separation (Δ GCS C) via 1C60* for MPo~C 60 in different organic solvents……………………………………………………….4 Charge-recombination rate-constants (k CR) for MPo~C 60 in different organic solvents…………………………………………….1 Formation constants calculated from Scatchard plots of absorbance data for the ‘two-point’ bound supramolecular dyads and triads in o-dichlorobenzene at 298 K…………………………… 130 5.2 B3LYP/3 -21G(*) optimized geometric parameters of the investiga ted supramolecular triads…………………………………………………132 5.3 Energy levels of the charge-separated states (Δ GRIP), free-energy changes for charge-separation (Δ GCS), and hole shift (ΔGHS ) for supramolecular triads in o-DCB……………………………………… 136 5.4 Fluorescence lifetimes (τf ),a quenching rate constants (kCS )b, and charge-separation quantum yields (F CS)b via 1ZnP*, and charge recombination rate constants (k CR) for supramolecular triads in o-DCB……………………………………………………….1 Crystal Data for the 3:5 dyad ………………………………………… 160 6.2 Fluorescence lifetimes (τf ) and fractions of slow and fast components……………………………………………………………. 176 xi LIST OF FIGURES 1.1 Schematic representation (a) excitation of chromophore (b) electron transfer and (c) energy transfer quenching of a chromophore excited state.2 Schematic representation of Marcus cur ve………………………….3 X–ray crystal structure and scheme of electron transfer in photosynthetic reaction center……………………………………….4 Covalently linked porphyrin-fullerene traids ………………………… 13 1.5 Covalently linked porpyrin-fullerene tetrad …….6 Covalently linked carotene-porphyrin-fullerene triads …………….7 Watson-crick hydrogen bonding porphyrin-fullerene dyad………… 18 1.8 Porphyrin dyads with base pair interactions ……………………….9 Porphyrin-fullerene dyad with crown ether-ammonium ion binding 21 1.10 Phthalocyanine-fullerene dyad with crown ether-quaternary ammonium ion binding ……………………………………………….11 Phthalocyanine-fullerene triad with crown ether- quaternary ammonium ion binding ……………………………………………….12 Porphyrin-fullerene traid with rotaxane-type interactions………….13 Fullerene-porphyrin rota xane via Cu(phen) 2 complex .14 Fullerene-porphyrin rota xane via Cu(phen) 2 complex .15 Host and guest complexation with π−π interactions ……………….16 Schematic diagram of porphyrin-fullerene aggregates in water ….17 Zinc porphyrin- stilbazole- pyromelliticdiimide, Donor-bridge-acceptor system……………………………………….18 Porphyrin-fullerene dyad with “tail-on” and “tail-off” binding mechanism……………………………………………………………… 30 xii 2.1 Synthetic scheme adopted for compounds 2 and 3………………… 35 2.2 General scheme for synthesis of fulleropyrrolidines ……………….1 Schematic diagram of photochemical events occur in dyads …….2 Synthetic scheme for compounds 7, 8, 9, and 10………………….3 Synthetic scheme for compounds 13, 14, 15……………………….4 Absorption spectra of 15 in (i) o-DCB, (ii) BN, and (iii) pyridine in the visible region.

The concentrations were held constant at 1.5 Visible spectral changes observed for 15 on increasing addition of pyridine in toluene………………………………………………….6 DFT B3LYP/3-21G(*) calculated geometric structures of 13 and 14…………………………………………………………………… 56 3.7 Frontier HOMO and LUMO of 13 calculated by DFT B3LYP/3 -21G(*) methods…………………………………………….8 DFT B3LYP/3-21G(*) optimized geometries of 15 (a) in the absence and (d) in the presence of bis-pyridine ligands. Figures b, c, e and f show the HOMO and LUMO of the dyad under the conditions described in a and d……………………………………… 59 3.9 Cyclic voltammograms of (a) 15 and (b) 14 (~0.05 mM) in o-DCB (0. Scan rate = 100 mV/s. The site of electron transfer is indicated on the top of the voltammograms….10 Fluorescence spectrum of (a) (i) 2, (ii) 13 and (iii) 14 in o-DCB (λex = 550 nm) and (b) (i) 1, (ii) 11 and (iii) 12 in o-DCB (λex = 515 nm)……………………………………………………………………….11 Fluorescence spectra of 3 (curves i, ii and iii) and 15 (curves iv, v, and vi) in o-DCB (curves i and iv), BN (curves iii and vi), and Py (curves ii and v) (λex = 565 nm in o-DCB, 566 nm in BN and 579 nm in Py).

The concentration of all of the species was held at 1.12 Fluorescence decay profiles of (a) 2, 13, and 15, and (b) 1, 11, and 12 in benzonitrile. The concentrations of porphyrins were maintained at 0.13 Time-resolved fluorescence spectra of 15 (a) toluene, (b) anisole, (c) o-DCB, and (d) BN………………………………………………… 71 3.14 Fluorescence decay profiles (a) 3 (600-700 nm) and (b) C60 (700-800 nm) and (c) 15 (700-800 nm) and (d) MgPO~C60 (600- 700nm) dyad in an argon saturated o-DCB (λex = 400 nm). The concentration of all of the species was held at 0.15 Nanosecond transient absorption spectra of 15 (0.05 mM) in argon saturated solution after the 532 nm-laser irradiation; (a) in o-DCB, and (b) in toluene after the 532 nm-laser irradiation. Figure inset shows the time profiles of the transient bands at the indicated wavelengths………………………………………………… 77 3.16 Energy level diagrams showing the photochemical events of the dyad 15 in (a) DMF, BN, o-DCB and anisole, and (b) toluene…… 81 4.1 Schematic diagrams of triads A (21: 2), B (21: 20), C (21: 19)….2 Synthetic scheme for compounds 16, and 17……………………….3 Synthesis of compound 18, and 19………………………………….4 Synthesis of fulleropyrrolidine 21…………………………………… 91 4.5 Spectral changes observed during the titration of 19 (1.88 μmol dm–3) with 21 (each 0.

addition) in o-DCB…………………….6 Optical absorption spectral changes of 20 on increasing addition of 21 in toluene ……………………………………………………….7 (a) Scatchard plot for triad A, absorbance changes observed at 422 nm, (b) Job’s plot for triad A, and (c) Job’s method of continuous variation plots for the triad C complex formation monitored at 424 and 429 nm………………………………………… 95 1 4.8 H NMR spectrum of 21 (5 mM) on addition of (a) 0, (b) 0.0 equivalents of 2 in CDCl3:CS2 (1:1 v/v)….9 B3LYP/3 -21G(*) optimized structure of 20 interacting with bis 98 pyridine functionalized fulleropyrrolidine 21………………………… 4.10 The B3LYP/3-21G(*) optimized structure, (b) HOMO, and (c) LUMO of the supramolecular triad C ……………………………….11 Cyclic voltammograms of (a) ZnTPP 2, (b) C60(Py) 2 21 and (c) isolated complex of triad A in o-DCB, 0. Scan rate = 100 mV/s………………………………………………………… 101 4. λex = 554 nm and λem = 646 nm……………….13 Steady state fluorescence spectra of 19 (1.88 μM) in the presence of 21 (0. each addition) in o-DCB.14 (a) Fluorescence spectra of 20 on increasing addition of 21 in toluene.

(b) Benesi-Hildebrant plot of binding constant analysis. (c) Stern-Volmer plot of quenching analysis……………………….15 Fluorescence decay profiles of (a) 20 (0.