Highly efficient polypyridyl-ruthenium(II) photosensitizers with chelating oxygen donor ligands: β-diketonato-bis(dicarboxybipyridine)ruthenium

A series of mono-cationic polypyridyl-ruthenium complexes with strongly electron donating β-diketonate ligands {(dcbp)2Ru(L)}Cl, where dcbp=4,4′-dicarboxy-2,2′-bipyridine; L=acetylacetonate (1), 3-methyl-2,4-pentanedionate (2), 1,3-diphenyl-1,3-propanedionate (3), have been synthesized as molecular photosensitizers for a nanocrystalline TiO2 electrode. In alkaline methanol solution, these complexes exhibit intense visible light absorption with low energy MLCT maxima above 517 nm which accompany a significantly enhanced band tail, improving red light absorptivity beyond 600 nm. The photoelectrochemical properties of these three diketonate complexes on a TiO2 semiconductor have been compared to cis-dithiocyanate complex, (dcbp)2Ru(NCS)2, which is one of the most efficient sensitizers reported to date. The diketonate complexes show quite high performances in photoelectrochemical cells containing I−/I3 − electrolyte. The overall solar light-to-electrical energy conversion efficiencies are in the range of 6.0–3.9% while the dithiocyanate complex yields 5.7% efficiency in our experiments.