Surface-Enhanced Resonance Raman Spectroscopy of Ru and Os Polyvinylpyridine Adsorbed on Silver Electrodes

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.