Photophysics and photostereomutation of aryl methyl sulfoxides

The effect of a methanesulfinyl group on the photophysics of several aromat ic chromophores is reported. The spectroscopic singlet and triplet energies are affected only modestly, compared to that parent arenes, but the fluore scence yields fall by at least 1 order of magnitude. Fluorescence lifetimes are short. Fluorescence enhancements are observed on cooling the sulfoxide s from room temperature to 77 K. High quantum yields of stereomutation are reduced as the temperature drops. There is not a consistent effect on tripl et or phosphorescence yields. It is proposed that these results are consist ent with a nonradiative pathway for deactivation of the singlet that result s in stereomutation. A modest activation energy of a few kcal/mol is estima ted for the photochemical racemization of 1-methanesulfinylpyrene