Prototropic equilibria of electronically excited molecules. Part IV. Some methoxybenzenes

Abstract

The fluorescence of anisole and the dimethoxybenzenes has been found to be quenched in aqueous solutions at acidities much lower than those necessary for ground-state protonation. This is in accord with the predicted increase in the basicity of these molecules upon excitation to their first singlet excited states. However the quenching is not accompanied by hydrogen exchange. This phenomenon is tentatively interpreted in terms of an incipient excited state proton exchange which, in its early stages, accelerates radiationless decay.