(JP7500630-W)      Ruthenium bis-(N-contg. heterocyclic ligand) complexes of formula (X)nRuLL1 (I) are new, where n is 1 or 2, pref. 2; X is Cl, SCN, H2O, Br, I, CN, NCO or SeCN; L1 is ligand of formulae (a)-(c); L is bipyridyl, phenanthroline, biquinolyl, 3-(2-pyridyl)-4-phenyl- 1,2,4-triazine, terpyridyl or 2,6-bis-(2-imidazolyl)-pyridine ligand of formulae (a)-(g); R is OH, H, 1-20C alkyl, ORa or N(Ra)2; and Ra is H or 1-4C alkyl.    Pref., X is Cl, CN, NCO or SCN; L1 is (a)-(c), esp. (a) or (b); R is OH, H or 1-20C alkyl, esp. H or 1-20C alkyl.    Cis- or trans-dithiocyanato- bis-(2,2'-bipyridyl- 4,4'-dicarboxylate) ruthenium (II) is claimed, most pref. being the cis-isomer (I').    USE/ADVANTAGE -   (I) are charge transfer sensitisers for titanium dioxide films or layers in photovoltaic cells, e.g. solar energy converters. Cells consisting of an electrically conductive layer deposited on a support to which one or more TiO2 layers have been applied are claimed, where (I) is applied as photosensitiser to the TiO2 layer. Typically (I) are used as charge transfer sensitisers for nanostructured TiO2 films (8-12 microns thick) with high internal surface area (roughened factor ca. 1000), prepd. by sintering 15-30nm colloidal TiO2 particles on a conducting glass support. Such films coated with a 1 micron monolayer of (I) harvest visible light efficiently (absorption threshold ca. 800nm), and can be incorporated in a thin layer regenerative solar cell with a light-reflecting counter electrode. (I) have good chemical stability and provide easy interfacial charge exchange with semiconducting solids. They have superior visible light harvesting ability to the tris-bipyridyl Ru(II) analogues. In nanostructure TiO2 film devices, (I) provide nearly quantitative conversion of incident photons into electric current over a large spectral range, giving a conversion efficiency comparable with silicon-based cells.    (US5463057-A)      Bi-pyridyl Ru complexes of formula (X)nRuLL1 (I) are new. n = 1 or 2. Each X is Cl, SCN, H2O, Br, I, CN, -NCV or SeCN. L is a ligand of formula (II) and L1 is a ligand of formula (a)-(g). Each R is OH, H, 1-20C alkyl, -ORa or N(Ra)2. Each Ra is H or 1-4C alkyl.    Specific (I) are cis or trans dithiocyanato-bis(2,2'- bipyridyl -4,4'-dicarboxylido-Ru and cis-dithiocyanate bis(2,2'-bipyridyl-4,4'-dicarboxylate)-Ru.    USE -   (I) are coated in TiO2 films for use in photovoltaic cells.    (EP613466-B1)      Ruthenium bis-(N-contg. heterocyclic ligand) complexes of formula (X)nRuLL1 (I) are new, where n is 1 or 2, pref. 2; X is Cl, SCN, H2O, Br, I, CN, NCO or SeCN; L1 is ligand of formulae (a)-(c); L is bipyridyl, phenanthroline, biquinolyl, 3-(2-pyridyl)-4-phenyl- 1,2,4-triazine, terpyridyl or 2,6-bis-(2-imidazolyl)-pyridine ligand of formulae (a)-(g); R is OH, H, 1-20C alkyl, ORa or N(Ra)2; and Ra is H or 1-4C alkyl.    Pref., X is Cl, CN, NCO or SCN; L1 is (a)-(c), esp. (a) or (b); R is OH, H or 1-20C alkyl, esp. H or 1-20C alkyl.    Cis- or trans-dithiocyanato- bis-(2,2'-bipyridyl- 4,4'-dicarboxylate) ruthenium (II) is claimed, most pref. being the cis-isomer (I').    USE/ADVANTAGE -   (I) are charge transfer sensitisers for titanium dioxide films or layers in photovoltaic cells, e.g. solar energy converters. Cells consisting of an electrically conductive layer deposited on a support to which one or more TiO2 layers have been applied are claimed, where (I) is applied as photosensitiser to the TiO2 layer. Typically (I) are used as charge transfer sensitisers for nanostructured TiO2 films (8-12 microns thick) with high internal surface area (roughened factor ca. 1000), prepd. by sintering 15-30nm colloidal TiO2 particles on a conducting glass support. Such films coated with a 1 micron monolayer of (I) harvest visible light efficiently (absorption threshold ca. 800nm), and can be incorporated in a thin layer regenerative solar cell with a light-reflecting counter electrode. (I) have good chemical stability and provide easy interfacial charge exchange with semiconducting solids. They have superior visible light harvesting ability to the tris-bipyridyl Ru(II) analogues. In nanostructure TiO2 film devices, (I) provide nearly quantitative conversion of incident photons into electric current over a large spectral range, giving a conversion efficiency comparable with silicon-based cells.