Oxoporphyrinogens: Electrochemistry, anion binding, and light induced electron transfer studies

Abstract

The research presented in this dissertation deals with the electrochemical, anion binding and photochemical studies of various oxoporphyrinogen systems. The first chapter provides a brief introduction to the material discussed in subsequent chapters. The second chapter discusses the electrochemical, spectroelectrochemical, computational (ab inito), and structural characterization of an extended family of N-substituted oxoporphyrinogens. The effect of increasing N-substitution on the electrochemical and spectroelectrochemical properties was systematically investigated. Chapter three focuses on the anion binding properties of the oxoporphyrinogens. The compounds were studied by optical and electrochemical methods to determine the response of the oxoporphyrinogens in the presence of anions. Chapter four deals with the electron/energy transfer processes occurring in supramolecular systems composed of oxoporphyrinogens and zinc porphyrin and the effect of functionalized fullerene when selfassembled to the systems. The photochemical measurements revealed energy transfer in nonpolar solvents, while in polar solvents electron transfer was possible and upon coordination to fullerene there was a higher degree of charge stabilization. The compounds discussed in this thesis were studied by optical absorbance and emission, electrochemical, and time-resolved photochemical methods. These compounds were mainly characterized by 1H NMR, UV-vis absorbance, and ESI-mass. Binding constants for the supramolecular complexes were calculated using UV-vis spectroscopic methods. Density functional theory (DFT) calculations were performed to gain insight concerning structural and orientation of the donor-acceptor groups in these supramolecular complexes. Electrochemical studies were performed to obtain free energy changes for charge separation and charge recombination and to find trends in the redox potentials with increasing N-substitution in the oxoporphyrinogens. Spectroelectrochemical measurements were carried out to find the peak positions of anion and cation radicals for the oxoporphyrinogens with the various substitutions. Steady state and time resolved fluorescence emission studies and transient absorption studies were employed to obtain charge separation and charge recombination rates and the lifetimes of the photo-induced electron transfer events.