Kenji Komaguchi
Hiroshima University, Graduate School of Engineering, Faculty Member
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... pyridine ring for OH11, the 4-phenylpyridine ring for OH14, and the quinoline ring for OH15 ... excitation are shown in Figure 5, which reveals an intramolecular charge transfer (ICT) from the ... The DSSCs were prepared by using the... more
... pyridine ring for OH11, the 4-phenylpyridine ring for OH14, and the quinoline ring for OH15 ... excitation are shown in Figure 5, which reveals an intramolecular charge transfer (ICT) from the ... The DSSCs were prepared by using the dye-adsorbed TiO2 electrode, Pt-coated glass as ...
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Charge-modulation spectroscopy was applied to vacuum-sublimed films of pentacene in the metal-insulator-semiconductor configuration with Parylene-C or cross-linked polymer as insulator. The spectrum exhibited several peaks in the... more
Charge-modulation spectroscopy was applied to vacuum-sublimed films of pentacene in the metal-insulator-semiconductor configuration with Parylene-C or cross-linked polymer as insulator. The spectrum exhibited several peaks in the wavelength range of 300-800 nm. The signal in the visible was ascribed to the field-modulation effect of a neutral pentacene film, while the three broad peaks in the UV exhibited field and frequency dependences different from those in the visible and were ascribed to the optical absorption due to a monocation radical of pentacene. This assignment was supported by the calculation reported earlier on the basis of the time-dependent density functional theory.
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A simple and safe technique which is based on glow discharge is demonstrated for stable encapsulation of H atoms in cage-shaped silsesquioxanes at room temperature, leading to the encapsulation yield of ca. 10(-4) H atoms per molecule for... more
A simple and safe technique which is based on glow discharge is demonstrated for stable encapsulation of H atoms in cage-shaped silsesquioxanes at room temperature, leading to the encapsulation yield of ca. 10(-4) H atoms per molecule for 10-minute discharging, much faster than the conventional gamma-ray irradiation technique.
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The cyclobutanone and cyclopentanone radical cations were generated in a halocarbon matrix by ionizing radiation at 77 K. The ESR spectrum of a cyclobutanone radical cation consisted of a triple-quintet hf structure with ca. 0.9 mT (2H)... more
The cyclobutanone and cyclopentanone radical cations were generated in a halocarbon matrix by ionizing radiation at 77 K. The ESR spectrum of a cyclobutanone radical cation consisted of a triple-quintet hf structure with ca. 0.9 mT (2H) and 2.4 mT (4H) splittings. Whereas, both cyclopentanone and 2,2,5,5-tetradeuteriocyclopentanone radical cations gave an identical triplet with 1.5 mT (2H) splitting. Based on the 1Hhf splittings, it was concluded that the SOMO in cycloalkylketone radical cations was changed from a πCH2 oribital to a n0 (and σC-C) orbital (i.e., πCH2- n0 orbital crossover) when the ring size increased from a four-member to a five-member.
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Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase,... more
Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.
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ABSTRACT An EPR study was carried out to investigate the structure and motional dynamics of the [(CH3)3N–CH2]+• radical formed in a γ-irradiated Al-offretite. Strongly temperature-dependent EPR spectra were observed in the temperature... more
ABSTRACT An EPR study was carried out to investigate the structure and motional dynamics of the [(CH3)3N–CH2]+• radical formed in a γ-irradiated Al-offretite. Strongly temperature-dependent EPR spectra were observed in the temperature range between 4 and 300 K. The observed 1H hyperfine (hf) splitting was a1=0.46 mT for three magnetically equivalent hydrogens, one of each methyl group at 110 K and a1′=0.15 mT for three of each methyl group at 300 K; the hf splittings due to two equivalent CH2 hydrogens and the central 14N were a2=2.24 and a3=0.35 mT, respectively, independent of the temperature. This result suggests that rotation of the methyl group around the N–CH3 bond is responsible for the temperature dependent line shapes. Assuming a three-site jump model in which three methyl protons interchange their positions with each other, the EPR line shapes were successfully analyzed by a simulation method using the jump rate as a variable parameter in the temperature range from 140 to 270 K. The rate was found to increase from 7.0×106 s−1 (140 K) to 4.1×108 s−1 (270 K) with temperature. From an Arrhenius plot of the rate constants, an activation energy of 8.1 kJ mol−1 was evaluated for the methyl group rotation of [(CH3)3N–CH2]+• in Al-offretite.
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A hydrogen atom-hydrogen molecule pair entirely isolated in an Ar matrix has been investigated by high-resolution ESR spectroscopy from 4.2 to 23 K. A doublet ESR spectrum of the hydrogen atom was separated by 51.18 mT and further split... more
A hydrogen atom-hydrogen molecule pair entirely isolated in an Ar matrix has been investigated by high-resolution ESR spectroscopy from 4.2 to 23 K. A doublet ESR spectrum of the hydrogen atom was separated by 51.18 mT and further split isotropically into nine lines with superhyperfine coupling constants of ca. 0.06 mT and peak intensities of 1:1:2:1:2:1:2:1:1 in a solid Ar matrix containing HD (3.3 mol%) at 20 K. The superhyperfine structure can be attributed to HHD and HD 2 pairs. The HD 2 pair is a product of the tunneling reaction HD + D → HD 2. The mean distance between the hydrogen atom and the hydrogen molecule in the tunneling reaction in the Ar matrix at 20 K is experimentally determined to be 1.73 Å.
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ABSTRACT Novel donor–π–acceptor (D–π–A) dyes composed of oligothiophenes having 3,4-ethylenedioxythiophene (EDOT) as a π-linker have been synthesized. The introduction of EDOT unit in oligothiophenes and the elongation of π-conjugation... more
ABSTRACT Novel donor–π–acceptor (D–π–A) dyes composed of oligothiophenes having 3,4-ethylenedioxythiophene (EDOT) as a π-linker have been synthesized. The introduction of EDOT unit in oligothiophenes and the elongation of π-conjugation length of oligothiophenes led to a red-shift of absorption bands of the D–π–A dyes. It was found that a D–π–A dye having EDOT-containing quaterthiophene exhibited the excellent light-harvesting ability up to 800 nm.
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ABSTRACT Recent progress in deuterium (D or 2H) labeling studies of radicals in the solid state is reviewed. Emphasis is placed on quantum effects at low temperature. The high-resolution EPR (ESR) spectra of selectively D-labeled methyl... more
ABSTRACT Recent progress in deuterium (D or 2H) labeling studies of radicals in the solid state is reviewed. Emphasis is placed on quantum effects at low temperature. The high-resolution EPR (ESR) spectra of selectively D-labeled methyl radicals were radiolytically generated together with a hydrogen atom methyl radical pair in an Ar matrix at cryogenic temperatures. The methyl radical spectra are discussed in terms of nuclear spin-rotation couplings using a three-dimensional free quantum-rotor model. A hydrogen atom hydrogen molecule (H···H2) pair formation in Ar is discussed in terms of D-isotope effects on quantum mechanical tunneling reaction. The H2 molecule as a “quantum solid” for high-resolution EPR spectroscopy is presented. D-effects on zero-point vibrational energy (ZPVE) are presented in combination with Jahn-Teller (J-T) distortion of some chemically important radical cations of methane, tetramethylsilane, cyclohexane and related radical cations whose mother molecules have high symmetrical structures such as Td and D3d. D-isotope effects on methyl group conformations are exemplified using selectively deuterated dimethylether and monofluoromethane radical cations; the experimental results were also interpreted in terms of ZPVE incorporated with the mass difference of the two hydrogen isotopes. Furthermore, a D-labeling study on bimolecular homolytic substitution (SH2) reactions by methyl radical in solid methylsilane (CH3SiH3) is presented.
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Microspheres of conducting poly(N-methylaniline) (PNMA) were successfully synthesized in aqueous solutions through chemical polymerization using only N-methylaniline as monomer, acid and oxidant without any templates. The microspheres... more
Microspheres of conducting poly(N-methylaniline) (PNMA) were successfully synthesized in aqueous solutions through chemical polymerization using only N-methylaniline as monomer, acid and oxidant without any templates. The microspheres were obtained only ...
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ABSTRACT In the cyclic voltammogram measured using a polyaniline (PANI) coated electrode in the presence of chloranil (CHR), the anodic peak potential of PANI was directly proportional to log[CHR]. A new absorption shoulder was evident at... more
ABSTRACT In the cyclic voltammogram measured using a polyaniline (PANI) coated electrode in the presence of chloranil (CHR), the anodic peak potential of PANI was directly proportional to log[CHR]. A new absorption shoulder was evident at around 450 nm in the UV–visible absorption spectrum of PANI after the electro-oxidation. These facts implied that PANI incorporated CHR. The measurements of the ESR spectra and the magnetic susceptibility (χg) of the PANI incorporating CHR revealed that the incorporation magnetized PANI. Although no ferromagnetic property was observed for the PANI, it had an unusual paramagnetic property because χg was not inversely proportional to temperature.
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ABSTRACT Reduced polyaniline (PANI) showed a Nernstian response to dissolved chloranil (CHR), linear electrode potential-log[CHR] relationship. The anodic peak potential (E-pa) of PANI in the cyclic voltammogram was directly proportional... more
ABSTRACT Reduced polyaniline (PANI) showed a Nernstian response to dissolved chloranil (CHR), linear electrode potential-log[CHR] relationship. The anodic peak potential (E-pa) of PANI in the cyclic voltammogram was directly proportional to log[CHR], i.e. linear E-pa-log[CHR] relationship. These linear relationships and the fact that the new absorption shoulder was evident at around 450 nm in the UV-visible absorption spectra implied that PANI incorporated with CHR. The measurements of the electron spin resonance (ESR) spectra and the magnetic susceptibility (chi(g)) of the PANI incorporating CHR revealed that the incorporation magnetized PANI. No magnetic hysteresis loop was observed for the PANI, and it showed no ferromagnetic property. However, it had an unusual paramagnetic property because chi(g) was not inversely proportional to temperature. In addition, from the ESR spectra, the polaron species (cation radicals) of PANI are delocalized along the entire polymeric backbones.
ABSTRACT Reduced polyaniline (PANI) showed a Nernstian response to dissolved chloranil (CHR), linear electrode potential-log[CHR] relationship. The anodic peak potential (E-pa) of PANI in the cyclic voltammogram was directly proportional... more
ABSTRACT Reduced polyaniline (PANI) showed a Nernstian response to dissolved chloranil (CHR), linear electrode potential-log[CHR] relationship. The anodic peak potential (E-pa) of PANI in the cyclic voltammogram was directly proportional to log[CHR], i.e. linear E-pa-log[CHR] relationship. These linear relationships and the fact that the new absorption shoulder was evident at around 450 nm in the UV-visible absorption spectra implied that PANI incorporated with CHR. The measurements of the electron spin resonance (ESR) spectra and the magnetic susceptibility (chi(g)) of the PANI incorporating CHR revealed that the incorporation magnetized PANI. No magnetic hysteresis loop was observed for the PANI, and it showed no ferromagnetic property. However, it had an unusual paramagnetic property because chi(g) was not inversely proportional to temperature. In addition, from the ESR spectra, the polaron species (cation radicals) of PANI are delocalized along the entire polymeric backbones.
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This paper contains three results. First, the rate constants for the tunneling reaction HD + D → H + D2in solid HD increase steeply with increasing temperature above 5 K, while they are almost independent of temperature below 5 K. A... more
This paper contains three results. First, the rate constants for the tunneling reaction HD + D → H + D2in solid HD increase steeply with increasing temperature above 5 K, while they are almost independent of temperature below 5 K. A mechanism of a vacancy–assisted tunneling reaction is proposed to account for this temperature dependence. Second, a hydrogen atom and a hydrogen molecule form a van der Waals complex in the Ar matrix at 20 K, where the tunneling reaction HD + D →H + D2takes place in this complex. The analysis of well–resolved ESR spectra of the complex determined the distance between a hydrogen atom and a hydrogen molecule as 2.3 – 2.5 Å. Third, the decay rate constants of <img src="/fulltext-image.asp?format=htmlnonpaginated&src=W4T82504R683537X_html\10909_2004_Article_415476_TeX2GIFIE2.gif" border="0" alt=" $${\text{H}}_{\text{2}}^ - $$ " />anions in solid parahydrogen decrease with decreasing temperature below 6.6 K, attain the min...
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