Solid-phase synthesis and photoactivity of Ru-polypyridyl visible light chromophores bonded through carbon to semiconductor surfaces.

1,10-Phenanthroline (phen) was grafted to either indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or titanium dioxide (TiO) semiconductors (SC's) by electrochemical reduction of 5-diazo-phen. The phen ligand is bonded to the semiconductor at C5, and it can be handled in air. The semiconductor-phen (SC-phen) complexes displace both CHCN ligands from either cis-[Ru(Mebipy)(CHCN)] (Mebipy = 4,4'-methyl-2,2'-bipyridine), cis-[Ru(Bubipy)(CHCN)] (Bubipy = 4,4'-tert-butyl-2,2'-bipyridine), or cis-[Ru(pheno)(bipy)(CHCN)] (bipy = 2,2'-bipyridine; pheno = 1,10-phenanthroline-5,6-dione) dissolved in DCM/THF (4 h, 70 °C) to form the corresponding surface-bound SC-[(phen)Ru(bipyridyl)] chromophores. The identities of the SC-[(phen)Ru(Mebipy)], SC-[(phen)Ru(Bubipy)], and SC-[(phen)Ru(pheno)(bipy)] (SC = ITO, FTO or TiO) chromophores were confirmed by X-ray photoelectron spectroscopy (XPS); inductively coupled plasma mass spectrometry (ICP-MS); UV-vis and reflectance infrared spectroscopies; and cyclic voltammetry (CV). The data were compared to analogous Ru-polypyridyl control compounds dissolved in solution. A facile ketone-amine condensation solid-phase synthesis reaction between SC-[(phen)Ru(pheno)(bipy)] and [Ru(1,10-phenthroline-5,6-diamine)(bipy)] in ethanol (80 °C, 1 h) formed the dinuclear, bound chromophore SC-[(phen)(bipy)Ru(tpphz)Ru(bipy)] (tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine). Photoelectrochemical oxidation of hydroquinone and triethylamine under acidic, neutral, or basic conditions showed that the SC-chromophore photoanodes are active, and that TiO-[(phen)Ru(Mebipy)] is the most active and stable under basic- and neutral conditions. The dinuclear chromophore SC-[(phen)(bipy)Ru(tpphz)Ru(bipy)] was most active and stable under potentiostatic conditions in acid.