Photoreduction of benzo-1,4-quinone sensitised by metalloporphyrins

Abstract

Benzo-1,4-quinone quenches the triplet excited state of many metalloporphyrins in ethanol solution and the overall quenching rate constants are a simple function of the thermodynamic driving force for electron transfer. The resultant ion-pair can dissociate to separated ions or recombine to ground-state reactants. The latter process is spin forbidden but the presence of central metal ions with large spin–orbital coupling constants enhances the rate of geminate recombination. This enhancement is even more pronounced when the central metal ion is paramagnetic and no redox ions are observed.