Common Marcus type dependence of the charge transfer induced processes in the sensitization and quenching of singlet oxygen by naphthalene derivatives

The charge-transfer induced quenching processes of the lowest excited tripl et state (T-1) of naphthalene derivatives by ground-state oxygen and of sin glet oxygen O-2((1)Delta (g),) by ground state naphthalene derivatives have been investigated in three solvents of different polarity. Both deactivati on processes are described by one common Marcus type plot. The analysis of the data strongly indicates that exciplexes with the same degree of average partial charge transfer (pCT) and the same reorganization energy are forme d in the rate-determining step of both quenching processes. The free energi es of pCT complex formation are related to the corresponding free energy of complete electron transfer by DeltaG(CT) = f DeltaG(CET) With a common cor rective factor f, for T-1 and O-2((1)Delta (g)) deactivation. The reorganiz ation energy increases from 34 kJ mol(-1) in carbon tetrachloride to 92 kJ mol(-1) in acetonitrile. The charge transfer character is shown to be signi ficantly larger than 25% and to increase with increasing solvent polarity.