Solvent-Initiated Photochemistry of Transition Metal Complexes

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Dr. Patrick Hoggard, Department of Chemistry, Santa Clara University, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division to perform studies of radical chain reactions in solution which are initiated through the absorption of light by the solvent. Specifically, he will determine whether the initial oxidizing agent in chloroform solvent-initiated reactions is a peroxy radical or a hydroperoxide. Reactions in which the metal-based quantum yield increases with decreasing irradiation wavelength will be explored using osmium, molybdenum and palladium di- and tri-nuclear species in chlorinated solvents. Ruthenium bipyridine reactions will be probed under conditions where oxygen is not limiting in an attempt to discover photoreversible, temperature-hypersensitive systems. Examples of potential applications of these phenomena include systems that periodically change composition under irradiation, `smart` glasses that darken under irradiation above a given temperature, and photocatalytic systems for the destruction of halogenated hydrocarbons in water. The absorption of light energy is commonly used to initiate chemical reactions. When these reactions take place in chlorinated solvents, there is some ambiguity as to whether the reactants themselves absorb the energy, or whether the solvent molecules absorb the energy first and then transfer it to the reactants. This is an important mechanistic question because of the potential applications which can result from a clear understanding of these processes and the corresponding ability to manipulate them. Dr. Hoggard will examine a series of metal complex substrates with differing reduction potentials and search for new solvent-initiated photoreactions. He will also pursue photocatalysis studies of chlorohydrocarbon degradation in aqueous media as well as reactions which are hypersensitive to temperature. These types of photoreactions can have high quantum yields, and may have implications for the degradation of environmentally recalcitrant chlorinated hydrocarbons.