Chemical interactions in the surface-enhanced resonance Raman scattering of ruthenium polypyridyl complexes

Surface-enhanced resonance Raman scattering (SERRS) from the alpha-diimine complexes [Ru(bPM)(3)](2+) and [Ru(bpz)(3)](2+) is reported for the first time at a roughened silver electrode. In both cases, a possible adsorbate orientation has been proposed involving binding through nitrogen lone pair electrons to the silver surface, based on changes in band positions upon adsorption. The SERRS spectra of [Ru(bpm)(3)](2+) were found to change slightly with a change in applied potential. The relative intensity of the v(C6C6') band was found to be dependent on both excitation wavelength and applied potential. This was ascribed to an active charge transfer (CT) mechanism operating synergistically with the electromagnetic mechanism. No such CT activity was observed in [Ru(bpZ)(3)](2+). It is tentatively suggested that this behavior may arise from the different modes of adsorption of the two complexes.