Kenta Adachi

Controllable Adsorption and Ideal H-Aggregation Behaviors of Phenothiazine Dyes on the Tungsten Oxide Nanocolloid Surface

The monomer-aggregate equilibrium of four phenothiazine (PN) dyes, containing thionine (TH), methylene blue (MB), new methylene blue (NMB), and 1,9-dimethylmethylene blue (DMB), in the tungsten(VI) oxide (WO(3)) nanocolloid solution has been investigated by means of UV-vis spectroscopy. Addition of PN dye into the WO(3) nanocolloid solution brought about significant changes in the absorption spectrum, suggesting the formation of H-type (face-to-face fashion) trimer on the WO(3) nanocolloid surface. The adsorptivity of PN dyes onto the WO(3) nanocolloid surface was diminished by the raising the ionic strength, indicating the evidence of the electrostatic interaction between cationic PN dye and negatively charged WO(3) nanocolloids. The detail analysis of each spectral data provided insight into the effect of molecular structure of PN dyes on the adsorption and aggregation behaviors on the WO(3) nanocolloid surface. Moreover, in situ measurement of PN dye aggregation using the centrifugal liquid membrane (CLM) technique revealed that the aggregation of PN dyes on the WO(3) nanocolloid surface proceeded in a two-step three-stage (monomer --> dimer --> trimer) formation. The aggregation mechanism of PN dyes on the WO(3) nanocolloid surface was discussed on the basis of Kashas exciton theory.

Photocatalytic Degradation of Chlorinated Ethanes in the Gas Phase on the Porous TiO2 Pellets: Effect of Surface Acidity

The photocatalytic degradation of chlorinated ethanes was studied in a tubular photoreactor packed with TiO(2) pellets prepared by sol-gel method. The steady-state condition was not obtained, but the deterioration in the photocatalytic activity was observed during the irradiation. Effects of mole fractions of water vapor, O(2), and C(2)H(5)Cl or C(2)H(4)Cl(2) and reaction temperature on the photodegradation of C(2)H(5)Cl or C(2)H(4)Cl(2) were examined, and these data were compared with those obtained by the photodegradation of chlorinated ethylenes. On the basis of the products detected with and without oxygen in the reactants gas stream, we proposed the degradation mechanism. Measurement of diffuse reflectance infrared Fourier transform spectroscopy of pyridine adsorbed on the catalysts showed that decrease in the conversion for the photodegradation of C(2)H(5)Cl was attributable to the formation of Brønsted acid sites. Comparison of the data obtained with the TiO(2) and the sulfated TiO(2) (SO(4)(2-)/TiO(2)) pellets indicated that the photodegradation of C(2)H(5)Cl was suppressed by the presence of the Brønsted sites, but that of trichloroethylene was not affected. Such a difference is attributable to the adsorption process of these reactants on the acid sites on the catalyst surface.

Interfacial aggregation of thioether-substituted phthalocyaninatomagnesium(II)-palladium(II) complexes in the toluene/water system

The interfacial aggregation of three thioether-substituted phthalocyanine–magnesium(II) complexes, MgPc(SR)8, of (2,3,9,10,16,17,23,24-octakis-ethylthiophthalocyaninato)magnesium(II), [MgPc(SEt)8], (2,3,9,10,16,17,23,24-octakis-benzylthiophthalocyaninato)magnesium(II), [MgPc(SBz)8], and (2,3,9,10,16,17,23,24-octakis-benzhydrylthiophthalocyaninato)magnesium(II), [MgPc(SBh)8] were investigated in the toluene/water system by means of a centrifugal liquid membrane (CLM) method. Aggregation of MgPc(SR)8 molecules at the interface was significantly promoted by the complexation with soft metal ions such as Pd(II) and Hg(II) added to the aqueous phase. The interfacial adsorption of MgPc(SEt)8 was caused even in the absence of Pd(II) by the formation of a co-facial H-dimer, but the presence of Pd(II) promoted H-dimer aggregation at the interface. In the cases of MgPc(SBz)8 and MgPc(SBh)8, there was observed no significant self-aggregation, but in the presence of Pd(II), the interfacial aggregation of Pd(II) complexes of MgPc(SBz)8 and MgPc(SBh)8 proceeded remarkably. It was suggested that MgPc(SBz)8–Pd(II) and MgPc(SBh)8–Pd(II) could not form H-aggregates, because of the steric hindrance of benzyl or bezhydryl group, but they formed J-aggregates. Furthermore, MALDI-TOF/MS spectra indicated that oligomers of MgPc(SBz)8–Pd(II) complex were formed at the liquid/liquid interface. The present study demonstrated the first example of Pd(II)-induced interfacial aggregation of phthalocyanine derivatives at the liquid/liquid interface, and suggested the possibility of controlling the aggregate structure between H- and J-aggregates by the size of peripheral substitute groups.

Photochromic Properties of Tungsten Oxide/Methylcellulose Composite Film Containing Dispersing Agents

Tungsten oxide-based photochromic films which changed reversibly in air between colorless- transparent in the dark and dark blue under UV irradiation were prepared by using methylcellulose as a film matrix and polyols such as ethylene glycol (EG), propylene glycol (PG), and glycerin (Gly) as dispersing agents. Influence of the dispersing agents and water in the films on the photochromic behavior was systematically studied. Under UV irradiation, absorption bands around 640 and 980 nm increased and the coloring rate was the following order: Gly > EG > PG. An increase in the amounts of dispersing agents or water accelerated the coloring rate. By increasing the water content of the film, a new absorption peak appeared at ca. 775 nm and the Raman spectra indicated a shift of W-O-W stretching vibration to lower wavenumber which was due to the formation of hydrogen bonding. All absorption spectra were fit by three Lorentz functions, whose bands were ascribed to various packing of WO6 octahedra. After the light was turned off, the formation of W(5+) was stopped and bleaching occurred by the reaction with O2 in air to recover its original transparent state. We anticipate that the biodegradable photochromic films developed in this study can be applied in recyclable display medium and especially in detachable films for glass windows whose light transmission properties are changed by sunlight, i.e., for usage as an alternative of smart windows without applying voltage.

Kinetic characteristics of enhanced photochromism in tungsten oxide nanocolloid adsorbed on cellulose substrates, studied by total internal reflection Raman spectroscopy

The nanostructured tungsten(VI) oxide (WO3)/cellulose derivatives (cellulose (CE) and triacetyl cellulose (TACE)) hybrid films were prepared by a solution-dipping adsorption process, and their structure and optical properties have been investigated. Various techniques, including adsorption isotherm, transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), in situUV-Vis absorption, and in situ total internal reflection Raman spectroscopy, were used for the characterization of the WO3/CE and WO3/TACE hybrid materials. Under UV irradiation, the photochromism (colorless → blue) was confirmed from the WO3/CE hybrid film, although no coloration of the WO3/TACE hybrid film was observed. This distinct difference in the coloration suggested that the interfacial interaction between hydroxyl groups present on the surface of the CE substrate and WO3 nanoparticlesviahydrogen bonding plays a major role in the enhancement of photochromism in the WO3/CE hybrid system. Moreover, the joint evidence in in situUV-Vis absorption and in situ total internal reflection Raman studies clearly revealed that the photogenerated coloration is related to a partial reduction of W6+ cations into W5+ cations in the WO3/CE hybrid film. The findings in this study have great implications for the development of the novel green-functional inorganic/organic hybrid materials in optical devices.

Linear dichroism of Zn(II)-tetrapyridylporphine aggregates formed at the toluene/water interface.

The apparent circular dichroism (CD) and the linear dichroism (LD) spectra of the aggregates of achiral zinc(II)-5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP), formed at the toluene/water interface in a centrifugal liquid membrane (CLM) cell, were investigated by comparison with the microscopic CD and LD spectra of a single interfacial aggregate of ZnTPyP about 100 mum in length, measured by a microscope-spectropolarimeter. The interfacial ZnTPyP aggregate showed two types of flat trapezoidal shapes, one had a seedlike core at an edge (type I) and another a needlelike core at an edge (type II). The microscopic CD and LD spectra were observed by varying the angle between the parallel axis of the trapezoidal aggregate and the perpendicular axis of a polarized light for LD. The plot of the CD intensity against the LD intensity for a single aggregate, observed at a given wavelength, showed a rotated elliptical shape with a long axis through the origin, when the orientation angle was changed. From these results, it was concluded that the apparent CD spectra observed by the CLM-CD method were mainly due to the large linear dichroism of the aggregate. Both type I and type II structures showed two transition dipole moments, parallel and perpendicular to the long axis of the structure, but suggesting a more developed J-aggregate in type II structure. AFM measurements showed that the interfacial ZnTPyP aggregate had a multilayer structure, in which the unit monolayer thickness was 1.58 +/- 0.23 nm. Finally, the orientation angle of the interfacial aggregate in the CLM cell was estimated as 41 degrees -44 degrees to the rotating axis of the cell.

Two-phase Couette flow linear dichroism measurement of the shear-forced orientation of a palladium(II)-induced aggregate of thioether-derivatised subphthalocyanines at the toluene/glycerol interface

Formation of the Pd(II)-induced thioether-derivatised subphthalocyanine Subpc(SR)66 (R = Et (ethyl) or Bz (benzyl)) aggregate at the toluene/glycerol interface was investigated by means of a new in situ spectrophotometric method using two-phase Couette flow (TPCF). The shear-forced orientation of the aggregate of Subpc(SR)66–Pd(II) complexes formed at the toluene/glycerol interface was studied by their linear dichroism (LD) spectra. The H-aggregate of the Subpc(SEt)66–Pd(II) complex gave no LD signal, but the J-aggregate of the Subpc(SBz)66–Pd(II) complex clearly afforded LD spectra at a wide range of rotation speeds, suggesting a longer J-aggregate structure in the Subpc(SBz)66–Pd(II) system. The relaxation kinetics of the shear-forced orientation of the Pd(II)–Subpc(SBz)66 aggregate were observed after stopping the rotation and analysing using a multi-exponential decay equation. By increasing the Subpc(SBz)66 concentration in toluene, the fast relaxation fraction of 6.6–7.5 seconds decreased and the slow relaxation fraction of 292–322 seconds increased. The results obtained in this study demonstrate that the TPCF method is useful for studying the size distribution of aggregates formed at liquid/liquid interfaces.

Chirality induction and amplification in methylene blue H-aggregates viaD- and L-phenylalanine pre-adsorbed on the tungsten oxide nanocolloid surface

In the methylene blue (MB)–phenylalanine (Phe)–tungsten(VI) oxide (WO3) colloid ternary aqueous solution, the MB H-aggregates, which could recognize the chirality of D- and L-Phe, were formed and investigated by means of UV-Vis absorption and CD spectroscopy. These results demonstrate a chirality transfer and amplification from only the pre-adsorbed Phe molecules to MB aggregates formed on the WO3 colloid surface via non-covalent interactions.

Measuring the optical chirality of molecular aggregates at liquid–liquid interfaces

Some new experimental methods for measuring the optical chirality of molecular aggregates formed at liquid–liquid interfaces have been reviewed. Chirality measurements of interfacial aggregates are highly important not only in analytical spectroscopy but also in biochemistry and surface nanochemistry. Among these methods, a centrifugal liquid membrane method was shown to be a highly versatile method for measuring the optical chirality of the liquid–liquid interface when used in combination with a commercially available circular dichroism (CD) spectropolarimeter, provided that the interfacial aggregate exhibited a large molar absorptivity. Therefore, porphyrin and phthalocyanine were used as chromophoric probes of the chirality of itself or guest molecules at the interface. A microscopic CD method was also demonstrated for the measurement of a small region of a film or a sheet sample. In addition, second-harmonic generation and Raman scattering methods were reviewed as promising methods for detecting interfacial optical molecules and measuring bond distortions of chiral molecules, respectively.

Factors affecting oxygen evolution through water oxidation on polycrystalline titanium dioxide

The effect of physicochemical properties such as specific surface area, crystalline phase, crystallite size, and crystallinity of TiO2 on photocatalytic water oxidation was investigated. Two types of polycrystalline TiO2 samples which have different physicochemical properties were prepared by a sol–gel method. The photocatalytic activities of the TiO2 samples for water oxidation were evaluated by the O2 evolution rate from an aqueous silver nitrate solution under ultraviolet light irradiation. Comparison of the two types of TiO2 samples revealed that the specific surface area and crystalline phase were not related to the O2 evolution rate. In contrast, a linear relationship between the crystallite sizes and the O2 evolution rates was observed for most of the TiO2 samples. Crystal face selective Pt and PbO2 depositions on the TiO2 samples were observed by photocatalytic reduction of PtCl62− and oxidation of Pb2+ ions, respectively, indicating that the oxidation and reduction sites are separated on the surface. An increase in the crystallite size of the TiO2 promotes a spatial separation of the redox sites and suppresses the electron–hole recombination, leading to the enhancement of the photocatalytic activity.