9312918 Saltiel Photoisomerization in olefins having one or more conjugated double bonds will be studied. Progressively more complex olefins will be studied, starting from stilbenes, through 1,6-diphenylhexatrienes to bacteriorhodopsin. The question of diradicaloid versus zwitterionic twisted excited singlet states will be examined in the simpler olefins by evaluating medium, substituent, and structural effects on their photochemistry and spectroscopy. Emission and product quantum yields will be measured as functions of medium, temperature, and excitation wavelength. The method of principal component analysis with self-modeling (PCA-SM) will be used to analyze these data. From this analysis, intermediates and the mechanisms of the photoisomerization processes will be determined. %%% This grant from the Organic Dynamics Program supports the continuing work of Professor Jack Saltiel at Florida State University. Mechanisms of rotation about carbon-carbon double bonds that are induced by absorption of light in the visible or ultraviolet region will be studied. Of particular interest will be compounds that have alternating carbon- carbon double and single bonds. The most complex molecule in this study is bacteriorhodopsin, the visual pigment. Light emission and product yields, based on the amount of light absorbed, as a function of solvent, temperature and excitation wavelength will be treated by a modeling program. This treatment will allow a description of the mechanism of these photoisomerization reactions. ***
