Photophysical Properties of TiO2 Surfaces Modified with Dinuclear RuRu and RuOs Polypyridyl Complexes

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Abstract
The photophysical properties of nanoporous TiO2 surfaces modified with two new Ru(II)−(bpt)−Ru(II) and Ru(II)−(bpt)−Os(II) polypyridyl complexes are reported. These dyads have been prepared by a two-step synthetic pathway. In the first step, [Ru(dcbpy)2Cl2], where dcbpy is 4,4‘-dicarboxy-2,2-bipyridyl, was reacted with the bridging ligand 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt) to yield the mononuclear precursor Na3[Ru(dcbpy)2(bpt)]·3H2O. Subsequent reaction of this compound with either [Ru(bpy)2Cl2] or [Os(bpy)2Cl2] yields the Ru(II)−Ru(II) and Ru(II)−Os(II) dyads. Electrochemical data, together with time-resolved transient absorption spectroscopy and the investigation of the incident-photon-to-current-efficiency (IPCE), have been used to obtain a detailed picture of the photoinduced charge injection properties of these dyads. These measurements indicate that for the heterosupramolecular triad based on Ru(II)−(bpt)−Ru(II), the final product species obtained upon charge injection is TiO2(e)−Ru(II)Ru(III). For the mixed metal Ru(II)−(bpt)−Os(II) dyad, both metal centers inject efficiently into the semiconductor surface and as a result TiO2(e)−Ru(II)Os(III) is obtained as a single charge-separated product.