Contribution of electric-field-induced metal-free porphyrin dication to photocurrent in mixed solid of metal-free porphyrin and o-chloranil/Al Schottky-barrier cell

金沢大学大学院自然科学研究科先端機能物質Although a Al/H2tpp (5, 10, 15, 20-tetraphenylporphyrin) Schottky-barrier cell did not show a clear rectification property because of the large electric resistance of the H2tpp solid, the rectification property was remarkably improved when o-chloranil was added into the H2tpp solid. The short-circuit dark-current was observed for the Al/dye cells with the mixed solid in contrast to that with the pure H2tpp solid, and it increased with increasing molar ratio (R) of o-chloranil to H2tpp. Furthermore, a much larger photocurrent was observed for the mixed-solid cells than for the pure H2tpp cell, but in the former cells in contrast to the latter cell, the open-circuit photovoltage was approximately the same as the open-circuit dark-voltage. These results indicate that the photocurrent of the mixed-solid cells was from the photocorrosion of the Al electrode. The short-circuit photocurrent action spectra obtained by irradiating from the Al side followed the absorption spectra of the dye solid films on the Al substrate below the R value of about 1, but above R = 1.5, a clear difference was observed in the spectra. This difference arises because a small amount of metal-free porphyrin dications, which is hardly detected by UV-visible spectra, was produced in the immediate neighborhood of the Al electrode when spin-coated with a larger R value because of dark-corrosion of aluminum by both assistance of the hydrogen bonds (between H2tpp and o-chloranil) and the electric field (in a Schottky barrier built during the spin coating). Thus the metal-free porphyrin dications efficiently underwent a photoinduced charge-separation by the potential gradient in the Schottky barrier

Electrocatalytic Activity of Electropolymerized Meldola’s Blue toward Oxidation of Dopamine

To understand the kinetics of charge transfer from chemically modified electrodes to solution species, the authors have investigated the influence of poly (Meldola’s blue) on the kinetic parameters of dopamine oxidation by rotating disc electrode voltammetry. The polymer film fixed on electrode surfaces raised the dopamine peak current by a factor of 10 in a 0.1 mM solution; this electrocatalytic effect enables one to detect dopamine at concentrations of the order of 5 µM. The polymer film increased the standard heterogeneous rate constant of dopamine oxidation more than 10-fold and favored a two-electron transfer step, thus raising the dependence of the kinetic current on the electrode potential. These effects were independent of electron self-exchange between redox-active sites in the film. They arose from the incorporation of dopamine with the polymer. This binding interaction decreased with protonation of the polymer, because of electrostatic repulsion between the positively charged species

The Fluorescence Quenching of Zinc Porphyrins with the ω-[4-(4-Pyridyl)pyridinio]alkyl Group

The fluorescence of parent porphyrins in ZnPC2bpy+(n), (PC2bpy+(n), 5-[n-[2-[4-(4-pyridyl)pyridinio]ethoxyl]phenyl]-10,15,20-triphenylporphyrin bromide, n=2,3, and 4), and ZnPC8bpy+(3), (PC8bpy+(3), 5-[3-[8-[4-(4-pyridyl) pyridinio]octyloxy]phenyl]-10,15,20-triphenylporphyrin bromide), was effectively quenched in non-coordinating solvents, such as o-dichlorobenzene and dichloromethane, because the pyridyl group in bpy+ (ω-[4-(4-pyridyl)pyridinio]alkyl group) was coordinated to zinc in porphyrin. On the other hand, the fluorescence of parent porphyrins in ZnPC2bpy+(3), ZnPC2bpy+(4), and ZnPC8bpy+ (3) was partly quenched in such coordinating solvents as N,N-dimethylformamide and pyridine. However, only the fluorescence of the parent porphyrin in ZnPC2bpy+(2) was effectively quenched, even in coordinating solvents. The hydrophobic interaction between the porphyrin ring and bpy+ in ZnPC2bpy+(2) may be considerably large, for bpy+ in ZnPC2bpy+(2) is covalently linked to the ortho position of the phenyl group in ZnTPP, (TPP 5,10,15,20-tetraphenylporphyrin), by a short chain. The emission was effectively quenched by the photoinduced electron transfer from the porphyrin ring to bpy+, because the axial coordination or the hydrophobic interaction gave bpy+ access to the porphyrin ring

Photoelectrochemical Properties of Thin Films of Cadmium, Zinc, and Magnesium Porphyrins with Pyridyl Group

Cadmium and zinc porphyrins with pyridyl or aminophenyl group gave smaller activation energy for the transfer of the carriers photoproduced in the solid thin film and larger cathodic photocurrent in quinhydrone solution than tetraphenylporphyrinato-cadmium and -zinc. The properties may be ascribed to the molecular arrangement of the porphyrins in the film

Electrochemical growth and charge-transport properties of polyaniline/poly(styrenesulfonate) composite films

The kinetic parameters of charge transport in composite-modified electrodes were measured as a function of the electrode potential, film thickness, solution pH, and counter ion composition by electrochemical impedance spectroscopy. The impedance characteristics of composite films were analyzed on the basis of the diffusion-migration transport of both holes and protons in the film. Incorporation of the polyanion with the host matrix produced a more compact deposite. A slow growth of the composite film during electropolymerization was ascribed mainly to its low electronic conductivity caused by poor contacts among polyaniline chains. Poly(styrenesulfonic acid) lowered the coupled diffusion coefficient of the charge carriers by a factor of ten. The relationships between the kinetic parameters and the oxidation and protonation levels of polyaniline suggested that the rate of charge transport through the composite film was controlled by electron transport, which occurred probably via interchain electron hopping