| Evidence for both direct and excited state interfacial electron transfer pathways was observed on nanocrystalline TiO2 surfaces anchored with [Fe(LL)(CN)4]2− compounds, where LL are bidentate ligands, bpy (2,2′-bipyridine), dmb (4,4′-dimethyl-2,2′-bipyridine), and dpb (4,4′-diphenyl-2,2′-bipyridine). Electrons injected from [FeII(LL)(CN)4]2− to TiO2 surfaces with rate constants, kinj > 108 s−1. Electron recombination from TiO2 to [FeIII(LL)(CN)4]− took milliseconds to complete and was well described by second-order equal concentration kinetic model. The ionic strength of Li+ in acetonitrile solution influenced the electron injection quantum yields for [FeII(LL)(CN)4]2− sensitized TiO2. Intervalence charge transfer parameters for Fe(CN)6 4− ion pairs, mixed valence compounds, TiO 2 interfacial systems were compared. The total reorganization energies for intervalence charge transfer and metal-to-ligand charge transfer (MLCT) processes on dye-sensitized TiO2 surfaces were estimated to be ∼0.6 and ∼0.3 eV, respectively. It was found the total MLCT reorganization energies for the surface-bound [Fe(LL)(CN)4]2− were significantly larger than for those in fluid solutions.; The compounds, (TBA)4[Ru(CN)4(dcb)] and (TBA) 4[Ru(CN)3(tctp)], (TBA = tetrabutylammonium, dcb = 4,4 ′-(CO2−)2-2,2 ′-bipyridine and tctp = 4,4′-4″ -tricarboxylate-2,2′:6′,2 ″-terpyridine), were used as photosensitizers to make solvatochromic solar cells. Solvent control of the spectral sensitivity of these compounds in fluid solutions and anchored on TiO2 surfaces was studied.; Spin-crossover compounds, Fe(TMPA)(NCS)2 (TMPA = tris(2-pyridylmethyl)amine) and Fe(deeb)2(NCS)2 (deeb = 4,4′-diethylester-2,2 ′-bipyridyl) were studied. The single crystal structure of Fe(TMPA)(NCS) 2 was characterized by X-ray crystallography and variable temperature magnetic susceptibility measurements in the range of 5–300 K showed a wide hysteresis curve. The thermal induced magnetic properties of solid state [Fe(deeb)2(NCS)2] were measured. The absorbance spectra data showed that [Fe(deeb)2(NCS)2] was labile in fluid solutions. The absorption spectra showed extinction coefficients for MLCT bands that were temperature dependent, increased with decreasing temperature. Pulsed light excitation in acetonitrile solution produced high spin state, (t2g)4(eg*)2, within laser pulse. The high spin to low spin relaxation process fit well to a first-order kinetic model with a rate constant of 5.2 ± 0.5 × 106 s−1 at 275 K and the activation energy was ∼1200 ± 100 cm−1. Light induced high spin to low spin relaxation was also observed for iron complexes bound on nanocrystalline TiO2 and ZrO2 surfaces. |
