A SERRS spectroscopic investigation of nickel(ii) porphyrin complexes adsorbed at electrochemical interfaces

Abstract

Surface enhanced resonance Raman (SERRS) spectra of two water-insoluble metalloporphyrins, nickel(II) octaethylporphyrin (NiOEP) and nickel(II) tetraphenylporphyrin (NiTPP), are reported at a range of excitation energies and applied potentials. By comparison of the RR and SERRS spectra, it was determined that NiOEP adsorbs onto a silver electrode surface in an edge-on orientation, most probably with the meso-carbon atoms closest to the electrode surface. SERRS spectra were independent of applied potential, indicating that the porphyrin layer is stable throughout the potential range employed and that enhancement principally occurs through the electromagnetic mechanism. By contrast, the Raman spectra of NiTPP at the electrode surface suggest little affinity of NiTPP for the silver surface and possibly arise from RR scattering, rather than SERRS.