Photophysics and Photochemistry of Cyclic Enones

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This award is made in the Organic Dynamics Program to support the research of Dr. David Schuster of New York University on the photochemistry and photophysics of cyclic unsaturated ketones. Properties of triplet excited states and reaction intermediates formed in the photoexcitation of cyclic enones in the presence and absence of alkenes will be studied by nanosecond flash photolysis, photoacoustic calorimetry and time-resolved resonance Raman spectroscopy. The goal is to obtain data which will allow specification of the molecular structures and energies of singlet and triplet states, strained trans isomers of cyclic enones and of triplet 1,4-biradical intermediates. These studies will establish how energetic relaxation in cyclic enone triplets is affected by ring size and substitution and how molecular structure affects rates of spin inversions to ground states from triplet excited states, a matter of fundamental significance in organic photochemistry. Mechanistic studies of the synthetically important photocycloaddition of cyclic enones to olefins will be carried out. In particular, secondary deuterium isotope effects will be determined for quenching of enone triplets by alkenes and for formation of cycloadducts in order to determine if enone-alkene exciplexes of any kind are on the reaction pathway to triplet 1,4-biradicals.