A new efficient photosensitizer for nanocrystalline solar cells:: synthesis and characterization of cis-bis(4,7-dicarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II)

The complexes [NBu4](2n)[cis-Ru(H(2-n)dcphen)(2)X-2 (n=0 or 1; H(2)dcphen=4,7-dicarboxy-1,10-phenanthroline; X=Cl, CN or SCN) were synthesized and spectroscopically characterized as a new class of photosensitizers. The energy levels of the LUMO and HOMO of cis-[Ru(H(2)dcphen)(2)(NCS)(2)] were estimated to be -1.02 and 0.89 V (vs. SCE), respectively, slightly more positive than those of [NBu4](2n)[cis-Ru(H(2-n)dcbpy)(2)(NCS)(2)] (n=0 or 1; H(2)dcbpy=4,4'-dicarboxy-2,2'-bipyridine). A more intense and broader MLCT absorption of [NBu4](2n)[cis-Ru(H(2-n)dcphen)(2)(NCS)(2)] (n=0 or 1) than that of [NBu4](2n)[cis-Ru(H(2-n)dcbpy)(2)(NCS)(2)] (n=0 or 1) was observed in ethanol solution at around 525 nm in the visible region. It is demonstrated that the new complexes act as efficient light harvesting antennae for dye-sensitized solar cells. A [NBu4](2n)[cis-Ru(Hdcphen)(2)(NCS)(2)] sensitized nanocrystalline TiO2 film shows a remarkable solar light to electrical power conversion efficiency of 6.1% at 100 mW cm(-2) of AM 1.5.