Plasmon-catalysed decarboxylation of dicarboxybipyridine ligands in Ru(ii) complexes chemisorbed on Ag nanoparticles: conditions, proposed mechanism and role of Ag(0) adsorption sites

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+.