The performance of dye-sensitized solar and photoelectrochemical cells is strongly dependent on the light absorption and electron transfer events at the semiconductor−small molecule interface. These processes as well as photo/electrochemical stability are dictated not only by the properties of the chromophore and metal oxide but also by the structure of the dye molecule, the number of surface binding groups, and their mode of binding to the surface. In this article, we report the photophysical and electrochemical properties of a series of six phosphonate-derivatized [Ru(bpy) 3 ] 2+ complexes in aqueous solution and bound to ZrO 2 and TiO 2 surfaces. A decrease in injection yield and cross surface electron-transfer rate with increased number of diphosphonated ligands was observed. Additional phosphonate groups for surface binding did impart increased electrochemical and photostability. All complexes exhibit similar back-electron-transfer kinetics, suggesting an electron-transfer process rate-limited by electron transport through the interior of TiO 2 to the interface. With all results considered, the ruthenium polypyridyl derivatives with one or two 4,4′-(PO 3 H 2 ) 2 bpy ligands provide the best balance of electron injection efficiency and stability for application in solar energy conversion devices.

The photostability of [Ru(II)(bpy)(2)(4,4'-(PO(3)H(2))(2)bpy)]Cl(2) (bpy = 4,4'-bipyridine) on nanocrystalline TiO(2) and ZrO(2) films was investigated using a standard measurement protocol. Stability was evaluated by monitoring visible light absorbance spectral changes, in real time, during 455 nm photolysis (30 nm fwhm, 475 mW/cm(2)) in a variety of conditions relevant to dye-sensitized solar cells and dye-sensitized photoelectrosynthesis cells. Desorption (k(des)) and photochemical (k(chem)) processes were observed and found to be dependent upon solvent, anion, semiconductor, and presence of oxygen. Both processes are affected by oxygen with k(des) and k(photo) noticeably smaller in argon saturated solution. Desorption was strongly solvent and pH dependent with desorption rates increasing in the order: methanol (MeOH) ≈ acetonitrile (MeCN) < propylene carbonate (PC) < pH 1 ≪ pH 7. Photochemistry occurred in MeOH and PC but not in aqueous, 0.1 M HClO(4) and MeCN. The anion and solvent dependence of k(photo) strongly suggests the photoreaction involves ligand substitution initiated by population of metal centered d-d states. The relative stability of -PO(3)H(2)- versus -COOH-substituted [Ru(II)(bpy)(3)](2+) was also quantitatively established.

The complex [Ru(Mebimpy)(bpy)(OH(2))](2+) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine] and its 4,4'-(PO(3)H(2)CH(2))(2)bpy derivative on oxide electrodes are water oxidation catalysts in propylene carbonate and 2,2,2-trifluoroethanol (TFE) to which water has been added as a limiting reagent. The rate of water oxidation is greatly enhanced relative to that with water as the solvent and occurs by a pathway that is first-order in H(2)O; an additional pathway that is first-order in acetate appears when TFE is used as the solvent.

To probe light-induced redox equivalent separation and accumulation, we prepared ruthenium polypyridyl molecular assembly [(dcb)2Ru(bpy-Mebim2py)Ru(bpy)(OH2)]4+ (Rua II–Rub II–OH2) with Rua as light-harvesting chromophore and Rub as water oxidation catalyst (dcb = 4,4′-dicarboxylic acid-2,2′-bipyridine; bpy-Mebim2py = 2,2′-(4-methyl-[2,2′:4′,4″-terpyridine]-2″,6″-diyl)bis(1-methyl-1H-benzo[d]imidazole); bpy = 2,2′-bipyridine). When bound to TiO2 in nanoparticle films, it undergoes MLCT excitation, electron injection, and oxidation of the remote −Rub II–OH2 site to give TiO2(e–)–Rua II–Rub III–OH2 3+ as a redox-separated transient. The oxidized assembly, TiO2–Rua II–Rub III–OH2 3+, similarly undergoes excitation and electron injection to give TiO2(e–)–Rua II–Rub IVO2+, with Rub IVO2+ a known water oxidation catalyst precursor. Injection efficiencies for both forms of the assembly are lower than those for [Ru(bpy)2(4,4′-(PO3H2)2bpy)]2+ bound to TiO2 (TiO2–Ru2+), whereas the rates of back electron transfer, TiO2(e–) → Rub III–OH2 3+ and TiO2(e–) → Rub IVO2+, are significantly decreased compared with TiO2(e–) → Ru3+ back electron transfer.

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It has been found that the self-assembling peptide RADA 16-I forms a beta-sheet structure and self-assembles into nanofibers and scaffolds in favor of cell growth, hemostasis and tissue-injury repair. But its biophysical and morphological properties, especially for its beta-sheet and self-assembling properties in heat- and pH-denatured conditions, remain largely unclear. In order to better understand and design nanobiomaterials, we studied the self-assembly behaviors of RADA16-I using CD and atomic force microscopy (AFM) measurements in various pH and heat-denatured conditions. Here, we report that the peptide, when exposed to pH 1.0 and 4.0, was still able to assume a typical beta-sheet structure and self-assemble into long nanofiber, although its beta-sheet content was dramatically decreased by 10% in a pH 1.0 solution. However, the peptide, when exposed to pH 13.0, drastically lost its beta-sheet structure and assembled into different small-sized globular aggregates. Similarly, the peptide, when heat-denatured from 25 to 70 degrees C, was still able to assume a typical beta-sheet structure with 46% content, but self-assembled into small-sized globular aggregates at much higher temperature. Titration experiments showed that the peptide RADA16-I exists in three types of ionic species: acidic (fully protonated peptide), zwitterionic (electrically neutral peptide carrying partial positive and negative charges) and basic (fully deprotonated peptide) species, called 'super ions'. The unordered structure and beta-turn of these 'super ions' via hydrogen or ionic bonds, and heat Brownian motion under the above denatured conditions would directly affect the stability of the beta-sheet and nanofibers. These results help us in the design of future nanobiomaterials, such as biosensors, based on beta-sheets and environmental changes. These results also help understand the pathogenesis of the beta-sheet-mediated neuronal diseases such as Alzheimer's disease and the mechanism of hemostasis.

Solar fuels hold great promise as a permanent, environmentally friendly, long-term renewable energy source, that would be readily available across the globe. In this account, an approach to solar fuels is described based on Dye Sensitized Photoelectrosynthesis Cells (DSPEC) that mimic the configuration used in Dye Sensitized Solar Cells (DSSC), but with the goal of producing oxygen and a high energy solar fuel in the separate compartments of a photoelectrochemical cell rather than a photopotential and photocurrent.

The photodriven accumulation of two oxidative equivalents at a single site was investigated on TiO2 coloaded with a ruthenium polypyridyl chromophore [Ru(bpy)2((4,4'-(OH)2PO)2bpy)](2+) (Ru(II)P(2+), bpy = 2,2'-bipyridine, ((OH)2PO)2-bpy = 2,2'-bipyridine-4,4'-diyldiphosphonic acid) and a water oxidation catalyst [Ru(Mebimpy) ((4,4'-(OH)2PO-CH2)2bpy)(OH2)](2+) (Ru(II)OH2(2+), Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine, (4,4'-(OH)2PO-CH2)2bpy) = 4,4'-bis-methlylenephosphonato-2,2'-bipyridine). Electron injection from the metal-to-ligand charge transfer (MLCT) excited state of -Ru(II)P(2+) (-Ru(II)P(2+)*) to give -Ru(III)P(3+) and TiO2(e(-)) was followed by rapid (<20 ns) nearest-neighbor -Ru(II)OH2(2+) to -Ru(III)P(3+) electron transfer. On surfaces containing both -Ru(II)P(2+) and -Ru(III)OH2(3+) (or -Ru(III)OH(2+)), -Ru(II)OH2(2+) was formed by random migration of the injected electron inside the TiO2 nanoparticle and recombination with the preoxidized catalyst, followed by relatively slow (μs-ms) non-nearest neighbor cross-surface electron transfer from -Ru(II)OH2(2+) to -Ru(III)P(3+). Steady state illumination of coloaded TiO2 photoanodes in a dye sensitized photoelectrosynthesis cell (DSPEC) configuration resulted in the buildup of -Ru(III)P(3+), -Ru(III)OH(2+), and -Ru(IV)═O(2+), with -Ru(IV)═O(2+) formation favored at high chromophore to catalyst ratios.