Flash photoelectrochemical studies of the photoreduction of hexaamminecobalt(3+) in the presence of benzophenone

Abstract

A photoelectrochemical technique has been applied to the study of the photoreduction of Co(NH3)63+ in the presence of benzophenone. Currents due to the oxidation of benzophenone ketyl radical and the reduction of the Co(III) complex were monitored after flash irradiation. In basic alcoholic solution the initial amount of ketyl radical produced by the flash was significantly diminished in the presence of Co(III) complex. Also, the amount of Co(III) complex seen after the flash was lowered substantially in the presence of benzophenone. The reactivity of Co(III) and ketyl radical when both are present after a flash appears negligible, failing to account for the significant photoreduction observed immediately after the flash. These data suggest that the primary reaction pathway involves energy transfer from the excited benzophenone triplet to the Co(III) complex with subsequent decomposition to the Co(II) product. In acidic solution (pH 5.5), no significant sensitized photoreduction of the Co(III) complex was observed.