RESUMO
Plasmon-catalyzed decarboxylation reactions of Ru(II) bis(2,2'-bipyridine)(4,4'-dicarboxy-bipyridine) denoted as Ru(bpy)2(dcbpy) and Ru(II) tris(4,4'-dicarboxy-bipyridine) denoted as Ru(dcbpy)3 complexes in hydrosol systems with Ag nanoparticles (NPs) conditioned by the presence of Ag(0) adsorption sites on Ag NP surfaces have been revealed by surface-enhanced (resonance) Raman scattering (SERRS and/or SERS) spectral probing and monitoring further supported by factor analysis. Interpretation of the experimental results was based on an identification of specific marker bands of the Ru-dcbpy and of the Ru-bpy units. Furthermore, by a series of specifically targeted SERRS and/or SERS experiments complemented by UV/vis spectral measurements and TEM imaging of deposited Ag NPs, plasmon catalysis by charge carriers, namely hot electrons (e-) and hot holes (h+), has been established as the most probable mechanism of decarboxylation reactions undergone by the carboxylate-chemisorbed Ru-dcbpy units of the complexes. The presence of Ag(0) adsorption sites on Ag NP surfaces as the necessary condition of the reaction progress is in full accord with the charge carrier mechanism of plasmon catalysis. In particular, the neutral Ag(0) sites create the interface required for the transport of hot e- to H+ co-reactants complementing thus the C-C bond breaking and CO2 formation caused by hot h+.
RESUMO
Steady state and nanosecond time resolved luminescence (namely, (3)MLCT phosphorescence) of [Ru(bpy)3](2+) and of [Ru(bpy)2(dcbpy)](2+)/bpy=2,2'-bipyridine; dcbpy=2,2'-bipyridyl-4,4'-dicarboxylic acid/attached to Ag NPs (the former by the electrostatic bonding, the latter by chemisorption) in non-aggregated Ag NP hydrosol systems has been investigated, and compared to the luminescence characteristics of the complexes in aqueous solutions. The intensity decrease of the 452 nm (and/or 455 nm, respectively) main band and elimination of the short wavelength shoulders in the excitation spectra and the intensity decrease of the emission spectra observed for both complexes upon their attachment to Ag NPs is attributed to the overlap of the excitation spectra with the surface plasmon extinction (SPE) of Ag NPs. The overlap leads to a loss of excitation energy by SPE as well as to a decrease of the (1)MLCT to (3)MLCT intersystem crossing efficiency. The time-resolved luminescence study shows that the (3)MLCT phosphorescence lifetimes of both complexes are markedly (by 3 and 4 orders of magnitude, respectively) shortened upon their attachment to Ag NPs. Nevertheless, the (3)MLCT lifetime of the chemisorbed [Ru(bpy)2(dcbpy)](2+) is by at least one order of magnitude shorter than that of the electrostatically bonded [Ru(bpy)3](2+), which indicates, that the phosphorescence lifetimes of these luminophores are strongly affected by the type of Ag NP surface-luminophore bonding.