Ultrafast Spectroscopic Studies of Polyene Photochemistry

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In this project in the Physical Chemistry program of the Chemistry Division, Prof. Roseanne J. Sension of the Chemistry Department of the University of Michigan will investigate the redistribution of energy in condensed phase reactions of small polyene molecules, and the influence of solvent parameters on this redistribution. Simple diene and triene species which serve as prototypes of complex bioorganic molecules will be investigated . Specifically, femtosecond absorption spectroscopy will be used to investigate the cis-trans isomerization reactions of 1,3,5-hexatriene, 2,4-hexadiene, 1,3-butadiene, and the electrocyclic ring opening reaction of cyclohexadiene. The detailed mechanism of chemical transformation in fluid environments remains among the most important unresolved problems in chemistry. While much attention has been given to chemical reaction dynamics of isolated molecules in low pressure gas phase systems, the majority of interesting reactions from a biological, environmental,, or engineering perspective, occur in fluid condensed phase environments. The research done in this project will attack some of these problems in order to meet two goals. 1) To develop a detailed understanding of the role that the electronic structure of polyenes plays in their photochemistry, and 2) to develop a detailed understanding of the role that energy redistribution plays in controlling polyene reactions since this is the ultimate factor in most, if not all, chemical reactions, be they in condensed phases or in isolated molecules. The principles deduced from the studies carried out in this research on prototype molecules will have application to general condensed phase reaction dynamics.