MICRO-RAMAN SPECTROSCOPY OF MESO-TETRAKIS(P-SULFONATOPHENYL)PORPHINE AT ELECTRODE SURFACES

Micro-Raman techniques are used to acquire Raman spectra of a water-so luble porphyrin (meso-tetrakis(p-sulfonatophenyl)porphine) adsorbed on to smooth and roughened Ag electrodes. We combine such Raman studies w ith cyclic voltammetric measurements conducted for the porphyrin adsor bed onto smooth, polished Ag and Pt electrodes (both as functions of p H and electrode potential) and gain insight into the mechanism for pro tonation of monomeric porphyrin and formation of aggregates. It is ded uced that variation in the Raman spectrum, induced by potential and pH changes, is related to the interfacial proton concentration. Electroc hemical reduction of water and not the release of hydrogen from a coad sorbed porphyrin leads to the formation of the diacid that then is inc orporated into aggregates. Another finding is that electrochemically i nduced protonation and the concomitant aggregation of TSPP are reversi ble on a time scale defined by the diffusion of H-2 into bulk solution .