The compounds Ru(bpy)(2)(BTL)(PF6)(2) and Ru(deeb)(2)(BTL)(PF6)(2), where bpy is 2,2'-bipyridine, deeb is 4,4'-(C2H5CO2)(2)-bpy, and BTL is 9'-[4,5-bis(cyanoethylthio)]-1,3-dithiol-2-ylidene]-4',5'-diazafluorene, were found to have very high extinction coefficients in the visible region. In an acetonitrile solution, the extinction of Ru(deeb)(2)(BTL)(PF6)(2) was epsilon = 44 000 +/- 1000 M-1 cm(-1) at lambda = 470 nm. Two quasi-reversible oxidation waves, E-1/2 = +0.88 and + 1.16 V, and an irreversible reduction, E-pr = -1.6 V, were observed versus ferrocene (Fc(+/0)). At -40 degrees C, a state was observed with spectroscopic properties characteristic of a metal-to-ligand charge-transfer excited state, tau = 25 ns. This same compound Was found to photoinject electrons into TiO2 with a quantum yield Phi = 0.3 +/- 0.2 for 532.5 or 417 nm light excitation in a 0.1 M LiClO4/acetonitrile electrolyte. In regenerative solar cells, a sustained photocurrent was observed with a maximum incident photon-to-current efficiency of 0.4. The photocurrent action and absorptance spectra were in good agreement, consistent with injection from a single excited state.