This grant in the Organic Dynamics Program supports the research of Dr. Richard Caldwell at the University of Texas at Dallas. Specifically, the structure, lifetime and energetics of photochemically-generated reaction intermediates will be explored both experimentally and by computational methods. A better understanding of the behavior and properties of transient reaction intermediates will provide a fundamental basis for their role in the outcomes of photochemical processes. Alkene triplets and triplet biradicals will be photochemically generated and studied by conventional organic mechanistic methods to determine the reaction products and infer the identity of the intermediates; by laser flash photolysis to determine transient lifetimes and intersystem crossing rates; by time-resolved photoacoustical calorimetry to determine energies of transients; and theoretically by CAS-MCSCF computations of spin-orbit coupling in small model species. The combination of these methodologies will allow a fundamental understanding of intersystem crossing as well as the energy surfaces of these intermediates. Arylalkene triplets, Norrish II and other 1,4-biradicals, triplet state di-pi-methane biradicals and some unusual trans-cyclohexenes and -cyclopentenes resulting from the alkene triplets, will be studied.
