Surface-enhanced resonance Raman spectroscopy of Ru and Os polyvinylpyridine adsorbed on silver electrodes

Abstract

Surface-enhanced resonance Raman spectroscopy (SERRS) of [(PVP) _x M(bpy) ₂ Cl]Cl polymers (x=3, 10, 20, 100 with M=Ru; x=10 with M=Os) coated onto silver electrodes has been investigated and major bands in the spectra have been assigned. The SERR spectra of the adsorbed polymer layers are dominated by 2,2′-bipyridine assigned bands. Small changes in band positions owing to the oxidation of Os ^II to Os ^III were observed at a gold electrode in the 1400–1700 cm ^-1 region. The Ru metallopolymers are used as model systems for the quantification of the SERRS signal in polymer-modified electrodes. Plots of intensity vs. surface coverage of metal centres were obtained as a function of loading (py:M ratio) at a constant deposition mass and as a function of deposition mass at a constant loading. At low surface coverages the variation of attenuation adjusted intensity with loading can be modelled as a Langmuir isotherm with I/I _max =kc/(1+kc) (c=the concentration, in mol dm ^-3 , of Ru centres in the film; k=10.6). At higher coverages the increasing importance of bulk resonance Raman scattering led to substantial deviations from this equation. A model was proposed which shows similar but weaker dependence on loading. We propose that the discrepancy with observation may be explained by the actual samples having a longer path-length, and thus a greater attenuation, than predicted.