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 beta -diketonate ligands {(dcbp)(2)Ru(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)(2)Ru(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-/I-3(-) 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. (C) 2000 Elsevier Science B.V. All rights reserved.