Energy Partitioning Following Light Absorption by Organic Chemicals

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This renewal award, made in the Organic Dynamics Program, provides continued support for Dr. Peter Wagner's research on energy partitioning in photoexited organic molecules. Photoexcited ketones with limited structural flexibility will be studied to determine how atomic and orbital orientations affect hydrogen atom transfer. Temperature studies with substituted ketones will reveal whether substituents affect the rate of hydrogen transfer by enthalpic or entropic considerations. The application of these reactions to the synthesis of benzofurans and other heterocycles from o-acylphenyl ethers will be explored. Intramolecular hydrogen abstraction produces intermediates which have one unpaired electron on each of two carbon atoms, leading to a variety of products including cyclic products. The geometry of cyclization as well as how intersystem crossing of biradicals with the same spin occurs will also be pursued. Other reactions to be studied are the photoinduced cleavage of halogen atoms in halogenated phenyl ketones and the cycloaddition of alkenes to triplet benzenes. This research addresses basic questions of how molecular structure of compounds affects the localization of energy when exposed to light and the chemical reactivity of the resultant excited intermediates. The localization of energy in specific parts of molecules allows for selective reactions of synthetic interest and addresses questions of the effects of light on systems of biological interest.