The ruthenium polypyridyl compounds, Ru(dpp)(2)(deeb)(PF6)(2) (Ru-deeb) and cis-Ru(dPP)(2)(eina)(2)(PF6)(2) (Ru-eina), where dpp is 4,7-diphenyl-1,10-phenanthroline, deeb is 4,4'-diethyl ester-2,2'-bipyridine, and eina is 4-ethyl ester pyridine, have been prepared and characterized to sensitize nanocrystalline TiO2 (anatase) thin films. In neat acetonitrile at room temperature, Ru-deeb was emissive with lambda(em) = 675 nm, tau = 780 ns, and emission quantum yield phi(em) = 0.067, whereas Ru-eina was nonemissive with tau < 10 ns. The short lifetime and observed photochemistry for Ru-eina are consistent with the presence of low-lying ligand-field (LF) excited states. The metal-to-ligand charge transfer (MLCT) excited states of Ru-deeb were found to be localized on the surface-bound deeb ligand, and on the remote dpp ligand for Ru-eina. Interfacial proton concentration was employed to tune the relative sensitizer-semiconductor energetics. Injection quantum yields, phi inj, varied from similar to 0.2 at pH = 5 to similar to 1 at pH = 1, with a slope of similar to 0.15/pH for both compounds. At pH = 12, long-lived excited states were observed with phi inj < 0.05. At pH <= 2, phi inj became temperature-dependent for Ru-eina, but not for Ru-deeb. A mechanism is proposed wherein population of LF states at elevated temperatures lowers phi inj.