Yoshihisa Fujiwara

Observation of a local minimum on the S1 surface of cis-stilbene solvated in inert gas clusters.

This probably shows that either the deposited Ag functions as a catalyst for the succeeding Ag deposition or very small Ag clusters do not absorb 633 nm monitoring light. A detailed study is now under way. The IoWG change in Figure 3a was ca. 0.01 in optical density (OD). This means that OD will only be ca. low4 when the monitoring beam is incident vertically over the OWG. Thus, the OWG method proved to be very effective for monitoring surface photoreactions. We are now also testing OWGs having semiconductor films including conductive S n 0 2 and photoactive Ti02.

Effect of high magnetic fields on the reverse electron transfer process in an α-cyclodextrin inclusion complex of phenothiazine-viologen chain-linked compound

The effect of high magnetic fields (< 14 T) on the lifetime of a triplet biradical generated by a photoinduced intramolecular electron transfer reaction of the title compound has been studied in water at room temperature by using pulse-magnet laser flash photolysis apparatus. On increasing the magnetic field from zero to ca. 1 T, the lifetime of the biradical increases steeply, and then decreases gradually in higher magnetic fields. The lifetime at ca. 13 T is about 30% of that at 1 T. This drastic reversal of the effect is qualitatively interpreted by a spin-lattice relaxation (SLR) mechanism. The SLR induced by the anisotropic Zeeman interaction is responsible for the decrease in lifetime in the higher magnetic fields. The mechanism is discussed in detail based on model calculations.

A laser flash photolysis study of the effect of intense magnetic fields on the photoreaction of benzophenone in SDS micellar solution

Abstract The magnetic field dependence of the lifetime of the benzophenone ketyl-SDS-derived radical pair in SDS micellar solution is divided into three regions. In a low magnetic field (

Intramolecular excited‐state proton transfer in jet‐cooled 2‐substituted 3‐hydroxychromones and their water clusters

Intramolecular excited‐state proton transfer (ESPT) of 3‐hydroxychromone (3‐HC), 3‐hydroxyflavone (3‐HF) and 2‐(2‐naphthyl)‐3‐hydroxychromone (2‐NHC), and of their water clusters, was investigated in a supersonic expansion. The visible tautomer fluorescence excitation spectra of these compounds exhibit considerably well‐resolved vibrational structures, while no significant uv fluorescence excitation spectrum due to the normal form was observed. The upper limit of the rate constant of the tautomer formation was estimated to be 1.77×1012 s−1 for 3‐HC, 6.5×1011 s−1 for 3‐HF, and 1.54×1011 s−1 for 2‐NHC in supersonic expansion by simulation of the linewidth of the respective origin bands in the visible fluorescence excitation spectra. The order of rate constants of the tautomer formations in the supersonic free jet are consistent with that of the ESPT of these compounds in nonpolar solution. The fluorescence excitation and dispersed fluorescence spectra demonstrate 1:1 and 1:2 water complex formations of 3‐HF...

Laser flash photolysis studies of the magnetic field effects on the hydrogen abstraction reaction of 2-naphthylphenylcarbene in micellar solution

Abstract 2-Naphthylphenylcarbene in the triplet state, photochemically generated from 2-naphthylphenyldiazomethane, abstracts a hydrogen atom from a surfactant in aqueous micellar solution. The lifetime of the radical pair nad the yield of the free radicals generated in the reaction increase significantly on application of magnetic fields (less than 1 T). The effects of magnetic field on the reaction of diphenylcarbene and fluorenylidene in micellar solution are also discussed for comparison.

Magnetic orientation of single-walled carbon nanotubes or their composites using polymer wrapping

Abstract The magnetic orientation of single-walled carbon nanotubes (SWNTs) or the SWNT composites wrapped with polymer using poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV) as the conducting polymer were examined. The formation of SWNT/MEHPPV composites was confirmed by examining absorption and fluorescence spectra. The N,N-dimethylformamide solution of SWNT/MEHPPV composites or the aqueous solution of the shortened SWNTs was introduced dropwise onto a mica or glass plate. The magnetic processing of the composites or the SWNTs was carried out using a superconducting magnet with a horizontal direction (8 T). The AFM images indicated that the SWNT/MEHPPV composites or the SWNTs were oriented randomly without magnetic processing, while with magnetic processing (8 T), they were oriented with the tube axis of the composites or the SWNTs parallel to the magnetic field. In polarized absorption spectra of SWNT/MEHPPV composites on glass plates without magnetic processing, the absorbance due to semiconducting SWNT in the near-IR region in horizontal polarized light was almost the same as that in vertical polarized light. In contrast, with magnetic processing (8 T), the absorbance due to semiconducting SWNT in the horizontal polarization direction against the direction of magnetic field was stronger than that in the vertical polarization direction. Similar results were obtained from the polarized absorption spectra for the shortened SWNTs. These results of polarized absorption spectra also support the magnetic orientation of the SWNT/MEHPPV composites or the SWNTs. On the basis of a comparison of the composites and the SWNTs alone, the magnetic orientation of SWNT/MEHPPV composites is most likely ascribable to the anisotropy in susceptibilities of SWNTs.

Magnetic field effects and time-resolved EPR studies on photogenerated biradical from intramolecular electron transfer reactions in zinc-tetraphenylporphyrin-C60 linked compounds: contribution of relaxation mechanism due to spin–spin relaxation

Magnetic field effects (MFEs) and time-resolved EPR on photogenerated biradical from intramolecular electron-transfer reactions in zinc-tetraphenylporphyrin (ZnP)–C60 linked compounds (ZnP(4)C60 and ZnP(8)C60) with flexible four and eight methylene groups have been investigated in benzonitrile. At low temperature (288 K), the decay rate constant of the biradical decreased steeply in low magnetic fields (<0.1 T), and then increased gradually in middle magnetic fields (0.1 ≤ H ≤ 0.6 T) and finally became almost constant in high magnetic fields (0.6 ≤ H ≤ 1 T) in both ZnP(4)C60 and ZnP(8)C60. At high temperature (323 K), in contrast, the decay rate constant decreased slightly in low magnetic fields (<0.1 T), and then increased gradually in higher magnetic fields (0.1 ≤ H ≤ 1 T). Interestingly, the decay rate constants in higher magnetic fields (0.4 ≤ H ≤ 1 T) were larger than that in zero magnetic field. The reverse phenomena of the MFEs around 0.1 T and temperature dependence on the MFEs are explained by the contribution of spin–spin relaxation due to anisotropic Zeeman interaction to the relaxation mechanism and most likely ascribed to the properties of C60 anion radical due to the spherical π-system. The mechanism is also supported by the time-resolved EPR spectra.

Chain length dependence of high magnetic field effects on lifetimes of radical ion pairs linked by a methylene chain: interpretation by both spin—lattice and spin—spin relaxations

High magnetic field dependence of lifetimes of methylene-chain-linked radical ion pairs (RIPs) generated by photo-induced electron transfer from zinc(II) porphyrin to viologen has been confirmed in aqueous acetonitrile using a pulse magnet-laser flash photolysis apparatus. In the case of a short methylene chain it was first revealed that the dependence was definitely different from that for a long one, and was characterized by a reversal in the dependence. In addition to a long lifetime independent of the magnetic field, RIP in fields above 7T exhibited short lifetimes that depended on the field. These results were interpreted not only by spin-lattice (longitudinal) relaxation but also by spin-spin (transverse) relaxation in RIPs.

The ground state tautomer in the excited state relaxation process of 3-hydroxyflavone at room temperature

Abstract Very recently, the ground state reverse proton transfer in 3-hydroxyflavone (3-HF) has been reported to take place within 30 ps by picosecond transient absorption spectroscopy by Aartsma and co-workers. Here we present evidence of intervention of a long-lived ground state tautomer involved in the excited state relaxation process of 3-HF by transient absorption and two-step laser excitation fluorescence spectroscopy.

Magnetic Field Effect on Chemical Wave Propagation from the Belousov–Zhabotinsky Reaction

Effects of magnetic field (maximum field, 4 and 93 T(2) m(-1)) on the propagation speed of a chemical wavefront from the Belousov-Zhabotinsky reaction were studied in a thin glass tube. The downward and upward speed and the horizontal one are, respectively affected significantly by vertical and horizontal magnetic fields. Observations of the wavefront shape in magnetic fields showed that the magnetic force-induced convection causes the observed effects.