Photoinduced Electron and Energy Transfer in Molecular Assemblies

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This project of Thomas Meyer, University of North Carolina (Chapel Hill), in the Inorganic, Bioinorganic and Organometallic Chemistry Program, involves the study of photoinduced electron and energy transfer in molecular assemblies that include extended arrays of polypyridyl complexes of Ru(II), Os(II) and Re(I) as chromophores and various redox carriers coupling these arrays to electron donors and acceptors. The potentials of the latter moieties will be chosen to provide a free energy gradient so that electrons and holes migrate away from the initial excited state metal centers. The transient infrared and Raman resonance spectroscopies will be used to determine the sites of oxidation and reduction in the charge separated excited state. Systems will be synthesized for study of conversion of single-photon, single-electron events into multiple redox equivalents that are required for catalytic bond-forming reactions. These will be constructed around a metal oxo center that is catalytically active for the oxidation of alcohols to aldehydes. The conversion of light energy to chemical energy, as accomplished by plants during photosynthesis, has largely eluded scientists. In photosynthesis, a single photon stimulates multiple redox processes that lead to formation and cleavage of chemical bonds. This project draws upon recent advances in inorganic photochemistry to suggest ways that large molecular assemblies can be constructed that will generate a separated electron-hole pair that can be utilized to stimulate multiple redox events. Studies such as this lay valuable, and badly needed, ground work for ultimately utilizing solar energy for chemical processing.