PHOTOCHEMISTRY AND PHOTOPHYSICS OF AROMATIC SULFOXIDES .1. CHARACTERIZATION OF THE TRIPLETS AT CRYOGENIC TEMPERATURES

Aromatic sulfoxides are photochemically active molecules. Much of that reactivity has been attributed to the previously uncharacterized trip let states of these molecules. At 77 K in ether/isopentane/ethanol (EP A) glass, aromatic sulfoxides are shown to have weak phosphorescence. The triplet energies are a few kilocalories per mole higher than the c orresponding ketones; the diaryl sulfoxides are about 3 kcal/mol lower than the corresponding ketones, and the diaryl sulfoxides are about 3 kcal/mol lower than the corresponding aryl methyl sulfoxides. For ins tance the triplet energy of diphenylsulfoxide is 78 kcal/mol, whereas the triplet energy of methyl phenyl sulfoxide is estimated to be 81 kc al/mol. The lifetimes of emission are generally under 100 ms. From the diffuse vibrational structure of the spectra, the lifetimes, and the effect of solvent on the triplet energy, it is concluded that the trip lets are delocalized aromatic states that involve substantial charge t ransfer off the oxygen atom.