HETEROGENEOUS ELECTRON-TRANSFER REACTIONS AT LIQUID LIQUID INTERFACESSTUDIED BY TIME-RESOLVED ABSORPTION-SPECTROSCOPY/

The triplet excited state of water-soluble porphyrin has been found to be quenched by tetracyanoquinodimethane both in homogeneous solutions , in a water/acetonitrile mixture, and at the liquid/liquid interface between water and toluene. Time-resolved transient absorption spectros copy in total internal reflection excitation mode (in the liquid/liqui d interface case) is used to monitor the decay of the excited porphyri n triplet state. In homogeneous solutions, the quenching is efficient and diffusion controlled. Photoproducts are obtained with a high yield only with negatively charged porphyrins. In the case of heterogeneous electron transfer, kinetics data are obtained from the analysis of th e relevant mass transfer regime. (C) 1998 Elsevier Science S.A. All ri ghts reserved.