Ryo Baba

Photoelectrochromic properties of a spirobenzopyran derivative

Abstract In order to study the possible use of spiro compounds as optically-electrically controllable molecular switches, the electrochemical behavior of the photochromic spiropyran derivative 1,3,3-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2′-indoline) (SP-1) in dimethylformamide (DMF) solution was investigated. The electrochromic behavior, which is associated with a redox process of the nitro group occurring in the potential range of −1.8 V to + 0.8 V (vs. Ag quasi- reference electrode (QRE)), was observed at −42 °C by monitoring the absorption spectral changes and potential dependence of the colored species produced on switching the applied potential. Spectroelectrochemical and low-temperature proton nuclear magnetic resonance ( 1 H NMR) measurements revealed that the electrochromism of SP-1 can be attributed to the production of the radical anion of the closed-ring isomer via reduction and the open-ring merocyanine (MC) isomer via oxidation from either the photoinduced open-ring (MC) or closed ring (SP, spiropyran) isomers. On the basis of these observations, a photoelectrochromic three-state conjugated system was obtained. A number of possible unique applications in photoelectrochemical molecular switching are described.

Photoelectrochemistry of TiO2 particles: efficient electron transfer from the TiO2 particles to a redox enzyme

Electron transfer from photoexcited TiO2 particles to dissolve oxygen (O2), and then to an active center of superoxide dismutase (SOD), was investigated by a slurry electrode technique. As a result of electron transfer, the superoxide anion (O2−) was formed initially, and was then further converted effectively into H2O2 by SOD catalysis. At a constant applied potential of 0.6 V (vs. SCE), an increase in photocurrent resulting from oxidation of O2− and H2O2 on a SnO2 working electrode was observed. However, such an increase in photocurrent decreased rapidly on the addition of catalase, which is a scavenger of H2O2.

Colloidal CdS—Pt photocatalyst stabilized by pendant viologen polymer for photoinduced electron transfer and hydrogen evolution

Abstract Colloidal CdS was stabilized using a functionalized polymer for electron mediation. The kinectics of electron transfer from colloidal CdS to the electron mediator were studied using laser flash photolysis. In the presence of colloidal platinum, the photoinduced electrons were relayed to the platinum and hydrogen was evolved using a sacrificial electron donor. The efficiency of hydrogen evolution significantly increased when the pendant viologen polymer was used as stabilizing agent.

Magnetic field effect on electrochemical oscillations during iron dissolution

A fairly low magnetic field of ca. 30 mT was found to affect the period and the amplitude of the self-sustained current oscillation of an iron electrode. This was observed much distinctively when the direction of the applied field was normal to the electrode surface, i.e., non-magnetohydrodynamic (MHD) configuration. The Flade potential of the iron electrode was not affected by the magnetic field intensity of up to 4 T. The observed magnetic field effect was attributed to the depression of the natural convection in the vicinity of the electrode surface which was caused by the two local paramagnetic body forces, the magnetic field gradient force and/or the concentration gradient force.

Self-ordered film of hemicyanine derivative characterized by phase-sensitive optical second-harmonic generation

Second-harmonic generation coherent interferometry was applied to the characterization of the adsorbed layer of a hemicyanine derivative 4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DSM) on a fused silica plate. It was clarified that the DSM molecules on the substrate were self-aligned with their methylpyridinium group facing towards the hydrophilic silica substrate.

Spatiotemporal reaction propagation of electrochemically controlled non-linear iron current oscillator

Self-sustained non-linear electrochemical oscillation was investigated with an iron electrode under anodic polarization in an aqueous sulfuric acid solution. The propagation of the reaction front of an oxide formation and reduction along the iron wire electrode was successfully monitored by means of a 16-channel platinum potential probe array. A pulse of the current oscillation was found to consist of both a sequential propagation of the oxide reduction, which makes the rise of the current, and a random formation of the oxide at the electrode surface for the current decay. It was also shown that the traveling velocity of the oxide reduction increased as the potential of the iron electrode became more cathodic. A resistance inserted in series between an iron electrode and a potentiostat appeared to change the oscillation waveform and the propagation speed of the reduction front. When the propagation was blocked by an insulator coating or a small piece of plastic brick on the electrode, the rising current was disturbed and modulated, having independent occurrence of the reduction propagation at each separated branch of the electrode. These results suggest a coupling between the ohmic potential drop in the solution and the reaction propagation along the electrode surface.

SPATIOTEMPORAL PROPAGATION OF A NON-LINEAR ELECTROCHEMICAL REACTION OVER AN IRON ELECTRODE

Abstract Propagation of the reaction front of oxide formation and reduction along an iron electrode has been investigated when a self-sustained non-linear current oscillation is proceeding. It has been observed that a resistance inserted between the electrode and the potential source changes the oscillation waveform and the propagation speed of the reduction. This finding shows a coupling between the ohmic potential drop in the solution and the reaction propagation along the electrode.

Separate monitoring of reaction products formed at oxidation and reduction sites of TiO2 photocatalysts using a microelectrode

Abstract The distribution of reaction products at the irradiated surface of a TiO 2 -ITO (indium-tin oxide) composite film was measured electrochemically using a carbon disk microelectrode located adjacent to the film surface (50-500 μm). Under UV irradiation in 0.1 mM KCl aqueous solution, a sustained increase in the cathodic current at the microelectrode was observed in the vicinity of the TiO 2 surface, whereas next to the ITO surface, the current was observed to flow in the opposite direction (anodic). The magnitude of the current depended on the distance between the film and microelectrode. The cathodic current response next to the TiO 2 surface is due to the reduction of ClO − formed at the irradiated TiO 2 surface, and the anodic response near the ITO surface is attributed to the oxidation of intermediate species formed by the reduction of the dissolved oxygen on the ITO surface. These results clearly show the formation of a “localized battery” at the irradiated TiO 2 -ITO film and also that the reaction products at the oxidation and reduction sites of the photocatalysts can be monitored separately using the present microelectrode system.

Coherent interferometric analysis of the molecular orientation based on the study of the optical second harmonic generation

In this paper we introduce a different type of interferometric SHG measurement for the study of the controlled molecular orientation in LB films. This method utilizes a well-defined molecular film as an optically non-linear standard which is placed on the single face of a substrate, such as a fused quartz plate

Application of a pulsed laser-induced photopotential technique to the current doubling process on polycrystalline oxide semiconductor electrodes

Abstract The laser-induced photopotential was measured on n-ZnO and n-TiO 2 polycrystalline electrodes with and without a “current doubling reagent” HCOONa. The rise time of the photopotential was 5–10 ns. The origin of the photopotential, the kinetics and the mechanism of the current doubling process are discussed.