REDOX REGULATION IN RUTHENIUM(II) POLYPYRIDYL COMPLEXES AND THEIR APPLICATION IN SOLAR-ENERGY CONVERSION

Ruthenium(II) complexes of the type [Ru(dmbip)(Hdcbpy)X], [Ru(dmbip)(H dcbiq)X] and [Ru(dhbip)(Hdcbpy)X], where dmbip = 2, 6-bis(1-methylbenz imidazol-2-yl)pyridine, dhbip = 2, 6-bis(1-hexadecylbenzimidazol-2-yl) pyridine, H(2)dcbpy = 4, 4'-dicarboxy-2, 2'-bipyridine, H(2)dcbiq = 4, 4'-dicarboxy-2, 2'-biquinoline and X = Cl-, NCS-, CN- or H2O, have be en synthesized and spectroscopically characterized. They act as effici ent charge-transfer sensitizers, when anchored onto nanocrystalline Ti O2 films. The lowest-energy metal-to-ligand charge-transfer transition s in these complexes could be tuned from 500 to 590 nm by choice of ap propriate ligands and the highest occupied molecular orbital varied ov er 400 mV. Some of the complexes reported are emissive at room tempera ture. The ground- and excited-state pK(a) values of dcbpy complexes we re measured by spectrophotometric and spectrofluorimetric titration. R esonance-Raman spectra show bands characteristic of the dmbip and dcbp y-ligand for excitation at 468 nm, while excitation at 568 nm gave pre dominantly bands associated with the dcbpy ligand. The excited-state p K(a) values and the resonance-Raman data indicate that the lowest exci ted state is a metal to dcbpy or dcbiq ligand charge-transfer state.