Raman spectroscopy and electrochemistry of water-soluble porphyrins at a silver electrode

Abstract

Cyclic voltammetry and laser Raman spectroscopy were applied to investigate insitu the properties and structures of metal meso-tetrakis (p-sulfonatophenyl)porphyrins (MeTPPS, Me = Co, Fe, Mn, Cu, Ni) adsorbed on a silver electrode in 0.05 M H 2 SO 4 aqueous solution. The cyclic voltammograms for O 2 reduction were investigated by changing the metal cations in the porphyrin ring. Among the porphyrins examined, only CoTPPS shows catalytic behavior for O 2 electrochemical reduction. The Raman spectra of MeTPPS in aqueous solution are very similar to those of metal tetraphenylporphyrins (MeTPP), and the band assignments were carried out on the basis of the results for [FeTPP] 2 O. The Raman spectra of MeTPPS on a silver electrode were measured under a N 2 or O 2 atmosphere, changing the applied potentials and the metal cations in the porphyrin ring. Their spectra are very sensitive to metal cations, but not so to applied potential. Keywords: porphyrin, SERS, electrochemistry, dioxygen, silver electrode.