Reinvestigating 2,5-di(pyridin-2-yl)pyrazine ruthenium complexes: selective deuteration and Raman spectroscopy as tools to probe ground and excited-state electronic structure in homo- and heterobimetallic complexesElectronic supplementary information (ESI) available: Synthesis and analytical data, additional Raman spectra. See DOI: 10.1039/c1dt10960j

The mono- (1) and dinuclear (2) ruthenium(ii) bis(2,2′-bipyridine) complexes of 2,5-di(pyridin-2-yl)pyrazine (2,5-dpp), for which the UV/Vis absorption and emission as well as electrochemical properties have been described earlier, are reinvestigated here by resonance, surface enhanced and transient resonance Raman spectroscopy together with selective deuteration to determine the location of the lowest lying excited metal to ligand charge transfer (3MLCT) states. The ground state absorption spectrum of both the mono- and dinuclear complexes are characterised by resonance Raman spectroscopy. The effect of deuteration on emission lifetimes together with the absence of characteristic bipy anion radical modes in the transient Raman spectra for both the mono- and dinuclear complexes bridged by the 2,5-dpp ligand confirms that the excited state is 2,5-dpp based; however DFT calculations and the effect of deuteration on emission lifetimes indicate that the bipy based MLCT states contribute to excited state deactivation. Resonance Raman and surface enhanced Raman spectroscopic (SERS) data for 1and 2are compared with that of the heterobimetallic complexes [Ru(bipy)2(2,5-dpp)PdCl2]2+3and [Ru(bipy)2(2,5-dpp)PtCl2]2+4. The SERS data for 1indicates that a heterobimetallic Ru–Au complex forms in situupon addition of 1to a gold colloid. [ABSTRACT FROM AUTHOR]