Polypyrrolic systems : anion binding, photophysical properties, and electron transfer




Karnas, Elizabeth Theresa

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Anion Binding has recently emerged as an important field of study due to the role these small inorganic species play in a plethora of biological processes. Chapter 1 of this thesis describes the biological relevance and scientific justifications for studying the ability of synthetic molecules to transport or extract anions under interfacial conditions. This chapter also serves to underscore the need to study both the thermodynamics and kinetics of anion binding as achieved using synthetic receptors. Methods for determining the thermodynamics of ion recognition are well-developed, and many equilibrium analyses of supramolecular binding events have been reported; however, the kinetics of such interactions are often neglected. Chapter 2 details the author's efforts to address this deficiency with respect to anion-binding and reports progress towards quantitative kinetic analyses of the interaction between cyclo[8]pyrrole (C8), an expanded porphyrin, and two test anions. It has been determined that stopped-flow analysis can provide on and off-rates, as well as activation parameters not accessible through thermodynamic means. Initial flash photolysis kinetic studies have also revealed that C8 has the potential to act as a photosensitizing agent through electron donation. This work is presented in Chapter 3, wherein the author discusses the construction of novel donor-acceptor dyads based on C8. As detailed in this chapter, time-resolved optical analyses have confirmed that photoinduced electron transfer occurs under conditions of photoexcitation and that the lifetime of the charge separated state is approximately 300 [mu]s. Finally, Chapter 4 describes a comprehensive set of spectroscopic work conducted by the author involving porphyrin and porphycenes that have a RuCp* (Cp*: pentamethylcyclopentadienyl) fragment either coordinated to the central porphyrinic core or directly attached to the "[pi]-face" of the macrocycle. These systems display unique intramolecular electron transfer properties that are ascribed to the metallated-porphyrin core acting as an electron acceptor, as opposed to a donor as is normally observed with porphyrins.




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