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 2 ) 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 CH 3 CN ligands from either cis -[Ru(Mebipy) 2 (CH 3 CN) 2 ] 2+ (Mebipy = 4,4′-methyl-2,2′-bipyridine), cis -[Ru( t Bubipy) 2 (CH 3 CN) 2 ] 2+ ( t Bubipy = 4,4′- tert -butyl-2,2′-bipyridine), or cis -[Ru(pheno)(bipy)(CH 3 CN) 2 ] 2+ (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) 2 ] 2+ chromophores. The identities of the SC-[(phen)Ru(Mebipy) 2 ] 2+ , SC-[(phen)Ru( t Bubipy) 2 ] 2+ , and SC-[(phen)Ru(pheno)(bipy)] 2+ (SC = ITO, FTO or TiO 2 ) 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)] 2+ and [Ru(1,10-phenthroline-5,6-diamine)(bipy) 2 ] 2+ in ethanol (80 °C, 1 h) formed the dinuclear, bound chromophore SC-[(phen)(bipy)Ru(tpphz)Ru(bipy) 2 ] 4+ (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 2 -[(phen)Ru(Mebipy) 2 ] 2+ is the most active and stable under basic- and neutral conditions. The dinuclear chromophore SC-[(phen)(bipy)Ru(tpphz)Ru(bipy) 2 ] 4+ was most active and stable under potentiostatic conditions in acid. Solid-phase synthesis of monomeric and dimeric Ru-polypyridyl visible light chromophores.