This grant in the Organic and Macromolecular Chemistry Program will support research by Prof. Jack Saltiel, which is concerned with determining the mechanisms, or step-by-step details, of selected chemical reactions caused by the absorption of light. A detailed understanding of such relatively simple reactions is an essential step toward the elucidation of complex light-initiated processes such as the vision sequence or the in vivo chemistry of Vitamin D. This work continues research heretofore supported by Foundation grant CHE-8400706. Specific research projects in Dr. Saltiel's program are divided into two areas. The first topic of study concerns alkene photoisomerization, and the second concerns electrocyclic reactions of arenes. Within the former are included investigations of (a) ground-state conformational control of the photophysics and photochemistry of arylethenes, including the analysis of conformationally rigid analogues; (b) the photochemical formation of trans-cyclohexenes and their chemistry; and (c) the mechanism of nonvertical triplet and singlet energy transfer, and the shape of stilbene's lowest triplet and lowest singlet potential energy surfaces. The interest in ground-state conformational control has been heightened by successful application of principal component analysis to the resolution of complex experimental spectra into the contributions from individual conformers. The second area of study has as its major theme the role of triplet-triplet annihilation as a pathway to arene photochemistry. Spectroscopic observations on transient intermediates will provide rate constants for the interpretation of steady-state data.
