Photophysics and photostereomutation of Aryl methyl sulfoxides

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