Photoinduced charge transfer processes of triplet benzophenone in acetonitrile

Photoconductivity experiments of benzophenone in acetonitrile under nanosecond laser flash photolysis conditions result in the production of ions. Irradiation with laser energies of 3.5 eV and 4.7 eV reveals different ionization mechanisms. On excitation at 355 nm, the photocurrents are observed on the microsecond timescale. Energetic considerations and comparison of the experimental traces (variation in the ground state benzophenone concentration, laser pulse intensity and oxygen concentration) with simulations indicate that the ion-generating process at 355 nm is due to triplet-triplet annihilation. On excitation at 266 nm, a monomolecular biphotonic process is operative, resulting in the observation of photocurrents within the laser pulse. This difference is explained by the energy requirements of these processes, taking into account the dipole-induced dipole solvation interaction. (C) 1997 Elsevier Science S.A.