Normal, resonance enhanced, and surface enhanced raman spectra of ruthenium-pyridyl complexes

Abstract

Normal Raman (NR) spectra of solid and solution phase 2,2′-bipyridine and solid phase Ru(bpy)(PVP)(ClO 4) 2 are shown. Resonance Raman (RR) spectra of solid and solution phase Ru(bpy)(pyr) 4 (ClO 4) 2 and Ru(pyr) 6 (BF 4) 2 are presented. Surface-enhanced Raman (SER) spectra of 2,2′-bipyridine, Ru(bpy)(pyr) 4(ClO 4) 2, (Ru(pyr) 6(BF 4) 2, and Ru(bpy)(PVP)(ClO 4) 2 at silver electrodes are presented. Above, pyr=pyridine, bpy-2,2′-bipyridine, and PVP=poly(4-vinylpyridine). The effect of elctrode potential on the SER spectra of these compounds is shown by spectra acquired at applied potentials from 0.0 to −1.0 V, and plots of SER intensity vs. electrode potential. Excitation profiles for selected bands of each compound are presented. Comparison of SER spectra of Ru(bpy)(pyr) 4(ClO 4) 2 and polymeric Ru(bpy)(PVP)(ClO 4) 2 suggests no potential effect intrinsic to the SER mechanism. Plots of SER intensity vs. electrode potential show the SER effect is dependent on the individual surface-active species. SER excitation spectra for these compounds show that colored ruthenium complexes exhibit a maximum with respect to excitation wavelength. The SER maxima are shifted toward longer wavelengths in comparison with the known UV-vis solution absorbance maxima.