Solvent dependence of (sub)picosecond proton transfer in photo-excited [2,2′-bipyridyl]-3,3′-diol

We report on (sub)picosecond fluorescence studies of the mono- to diketo tautomer reaction in photo-excited [2,2′-bipyridyl]-3,3′-diol in aprotic and protic solvents. In aprotic solvents no influence of the nature of the solvent, temperature and deuteration of the hydroxyl groups on the proton transfer dynamics was found. In protic solvents, however, the proton transfer time is found to change proportionally with the viscosity coefficient of the solvent. We briefly discuss (i) the formation of the mono- and diketo forms from the dienol form and (ii) the nature of the vibrational modes assisting in the proton transfer process.