Shinichiro Nakamura

Calculation of the absorption wavelength of dyes using time-dependent density-functional theory (TD-DFT)

The absorption wavelengths and oscillator strengths of a series of organic dyes important for the dye industry (indigo, azobenzene, phenylamine, hydrazone, anthraquinone, naphthoquinone and cationic dyes) were calculated using time-dependent density-functional theory. The results were compared with experimental data. TD-DFT correctly reproduced the visible absorption of the dyes.

Theoretical study of an intermediate, a factor determining the quantum yield in photochromism of diarylethene derivatives

Experimental and theoretical joint study on the photochemical reaction mechanism of photochromic diarylethenes is presented. An intermediate, suggesting an important role for the determination of the quantum yield, is proposed by ab initio multiconfiguration self-consistent (MCSCF) calculation.

Raman spectroscopic study on photochromic reaction of a diarylethene derivative

Abstract Photochromic reaction of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene has been studied by FT-Raman spectroscopy. The Raman bands in the 1300–1700 cm −1 region of the open-ring isomer of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene are clearly distinguished from those of the closed-ring isomer. The vibrational assignment has been made by measuring the polarized Raman spectrum and density functional theory calculations at the B3LYP/6-31G** level.

Theoretical study on novel quantum yields of dithienylethenes cyclization reactions in crystals

Abstract Novel quantum yields (QYs) of photochromic cyclization reactions are studied for 1,2-bis (2-methyl-5-phenyl-3-thienyl) perfluorocyclopentene (1) and 1,2-bis (2-methyl-1-benzothiophen-3-yl) perfluorocyclopentene (2). The difference of the QYs in crystals and hexane solution for the molecules 1 and 2 is explained by their initial geometries, the relaxation from the Franck–Condon states, the shapes of the potential energy surfaces of the ground state, and the geometry change by the large amplitude motions.

Micrometer-scale photochromic recording on amorphous diarylethene film and nondestructive readout using near-field IR light

An amorphous photochromic recording film was prepared by spin coating a solution of a diarylethene derivative having bulky m-terphenyl groups. Near-field IR detection was carried out to read out the photochromic recording spots recorded by green laser irradiation on the film, and a spot with a diameter of approximately 5 µm was nondestructively read out by the technique. The spot size was smaller than the wavelengths used for the read out, indicating the advantage of using the near-field technique.

Hydroesterification of ethylene catalyzed by Pd(II) complexes: an ab initio MO study

Abstract An ab initio MO study showed that hydrido-Pd species would be a preferable key intermediate instead of alkoxycarbonyl-Pd species in the Pd(II)-catalyzed hydroesterification of ethylene.

Lattice dynamics and optical properties of yttrium oxysulfide

Abstract Lattice dynamics and optical properties of yttrium oxysulfide have been investigated with the combination of microscopic Raman scattering experiment and first-principles calculation. The Raman scattering experiment on our single crystals ensures an earlier Raman spectrum based on powdered samples. Ab initio calculation based on density-functional perturbation theory is performed to obtain the phonon modes in the first Brillouin zone, dielectric and Born effective charge tensors in the uniaxial crystal structure. A rigorous assignment of all the phonon modes at Γ-point is achieved, in agreement with the previous and present Raman experimental data. The calculated results also indicate the ambiguity of infra-red experimental results on oxysulfides. Since these physical values are related to the properties of polaron, our theoretical approach may be useful to understand optoelectronic processes such as scintillation.

Nonlinear cathodoluminescence from insulators

Abstract White emission of high luminance is observed at room temperature for powder layers of various insulators under intense electron-beam irradiation. This emission appears at a threshold current density, typically about 0.02–0.2xa0mA/cm2 at 25xa0kV accelerating voltage. Its intensity increases steeply with an increase in the beam current. Spectral distribution of the emission is very broad with a peak in the near-infrared region. However, the nonlinear current dependence of the luminescence intensity indicates that the emission is not thermal radiation. This emission was observed for some phosphors, e.g. SrHfO3:Tm, Y2O3:Eu and Y2O2S:Eu, and also for materials without activator ions, but not for materials with relatively high conductivity, such as ZnO or indium tin oxide. The emission appears strongly at a low threshold on edges or rims of grooves or holes made on a screen. These results indicate that high electric field induced by charges on insulator tips gives rise to the emission.

An ab-initio MO study on metal oxide catalytic surfaces

Abstract The activation of the Moue605O bond in mixed molybdenum oxide compounds has been studied by means of ab-initio MO methods on mono- and bi-nuclear metal oxide clusters. The clusters, containing Mo, Nb and V, have been chosen to represent the assumed catalytic sites of mixed molybdenum oxide compounds. The analysis of bond length and orbitals shows that the Moue605O bond can be activated by a neighboring metal oxide unit through the interaction of the molecular orbitals of the two sub-units. The present investigation thus shows that the juxtaposition of different metal oxide units in catalysts is not only important in providing a suitable geometry of the surface, but also in providing an indirect mechanism for activation and deactivation of catalytic sites via neighboring structural elements.

A study of QM/Langevin-MD simulation for oxygen-evolving center of photosystem II

We have performed three QM/Langevin-MD simulations for oxygen-evolving complex (OEC) and surrounding residues, which are different configurations of the oxidation numbers on Mn atoms in the Mn4O5Ca cluster. By analyzing these trajectories, we have observed sensitivity of the change to the configuration of Mn oxidation state on O atoms of carboxyl on three amino acids, Glu354, Ala344, and Glu333. The distances from Mn to O atoms in residues contacting with the Mn4O5Ca cluster were analyzed for the three trajectories. We found the good correlation of the distances among the simulations. However, the distances with Glu354, Ala344, and Glu333 have not shown the correlation. These residues can be sensitive index of the changes of Mn oxidation numbers.