Surface-enhanced resonance Raman spectroscopy of iron(II) and ruthenium(II) bipyridyl complexes adsorbed on silver sols

Abstract

Surface-enhanced resonance Raman scattering (SER RS) is reported for [Fe(bpy)₃]²⁺, [Fe(bpy)₂(CN)₂], [Febpy(CN)₄]^2– and [Ru(bpy)₃]²⁺ adsorbed on Ag sols. In each case the enhancement factor is approximately 10⁶, such that even very weak bands have appreciable signal-to-noise ratios, and a detection limit of ca. 10^–12 mol dm^–3 can be achieved. The band wave-numbers and relative intensities are not significantly different from those of the resonance Raman spectra of the free molecules, indicating that these species are not chemisorbed to the Ag particles. Thus, the enhancement is due solely to surface plasmon resonance, which also leads to quenching of the strong luminescence of the [Ru(bpy)₃]²⁺ ion. The first meaningful SER RS depolarization ratios have been obtained by careful control of the state of aggregation of the Ag sol.