Kunihiro Tokumura

Kanazawa University, Kanazawa-shi, Ishikawa-ken, Japan

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Publications (38)165.75 Total impact

  • Shigeru Kohtani · Misa Tomohiro · Kunihiro Tokumura · Ryoichi Nakagaki
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    ABSTRACT: Photooxidative degradations of nine polycyclic aromatic hydrocarbons (PAHs) using pure and Ag-loaded BiVO4 photocatalysts have been examined in acetonitrile under visible light irradiation. Photoproducts have been identified by means of gas chromatography–mass spectrometry (GC–MS). Silver fine particles loaded on BiVO4 surface improved the reaction rates of all PAHs degradations. In particular, anthracene and benz[a]anthracene (Bz[a]A) are efficiently oxidized to anthraquinone and benz[a]anthracene-7,12-dione, respectively. Photooxidation mechanism of anthracene and Bz[a]A has been clarified by the GC–MS analyses by the use of H218O as a reactant. It has been proved that OH radicals are generated through the oxidation of water by valence band holes on the Ag-BiVO4 surface in acetonitrile, and greatly contribute to the degradations of these PAHs. The OH radical attack to PAHs probably determines the overall rates of oxidation of PAHs on Ag-BiVO4 photocatalyst.
    Applied Catalysis B Environmental 06/2005; 58(3-4-58):265-272. DOI:10.1016/j.apcatb.2004.12.007 · 7.44 Impact Factor
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    ABSTRACT: Silver fine-particles loaded on BiVO4 photocatalyst by an impregnation method remarkably improve adsorptive and photocatalytic performance on the degradation of long-chain alkylphenols such as 4-n-nonylphenol (NP) and 4-n-octylphenol (OP). The Ag-loaded BiVO4 powders strongly adsorb NP and OP, which is attributable to silver oxides (Ag2O and/or AgO) partly covered on the silver surface. The specific adsorption property disappears when the surface silver oxides are reduced in a H2 stream. Degradation rates and CO2 mineralization yields for NP are increased by the Ag loading on BiVO4.
    Catalysis Communications 03/2005; 6(3-6):185-189. DOI:10.1016/j.catcom.2004.12.006 · 3.70 Impact Factor
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    ABSTRACT: A visible-light-driven photocatalyst, BiVO4, has been applied for degradation of a series of linear 4-n-alkylphenols under irradiation from a solar simulator. Degradation rates become faster with increasing alkyl chain length. Half-life of 4-n-nonylphenol (4-n-NP) is 18 min, which is about eight times shorter than that of phenol. The rate law of disappearance for heptyl-, octyl- and nonylphenols exhibits zero-order kinetics. The amount of adsorption on BiVO4 surface is much larger for longer hydrophobic alkylphenols. It is thus concluded that BiVO4 is suitable for degradation of hydrophobic alkylphenols such as nonyl- and octylphenols nominated as endocrine disruptors. Degradation of branched 4-nonylphenol (mixture of isomers) has also been examined, and disappearance of its estrogenic activity was confirmed by means of the yeast two-hybrid assay. A gas chromatography–mass spectroscopy (GC–MS) analysis after solid-phase extraction indicates that the major product is cis,cis-4-alkyl-6-oxo-2,6-hexadienoic acids, and the minor products are 4-alkylcatechols and 4-(1-alkenyl)phenols.
    Applied Catalysis B Environmental 11/2003; 46(3-46):573-586. DOI:10.1016/S0926-3373(03)00320-5 · 7.44 Impact Factor
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    ABSTRACT: A toxic endocrine disruptor, 4-n-nonylphenol, was degraded using a well-known TiO2 and a visible-light-driven BiVO4 photocatalyst under irradiation from a solar simulator. The degradation rates for both BiVO4 and TiO2 are comparable in air-saturated solution though surface area of BiVO4 is much smaller than that of TiO2. This fact indicates that BiVO4 has a great ability to degrade alkylphenols in wastewater under solar light.
    Chemistry Letters 07/2002; 31(7):660-660. DOI:10.1246/cl.2002.660 · 1.23 Impact Factor
  • Source
    Kunihiro Tokumura · Yumi Matsushita
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    ABSTRACT: Deoxygenation of 6-cyanophenanthridine 5-oxide (6CPNO) in the lowest triplet state was confirmed by triplet sensitization of proflavine with visible S1←S0 absorption band (λmax=460nm) in ethanol. Absorption bands of 6-cyanophenanthridine (6CP) grew up at the expense of those of the N-oxide in a selective steady-light (>420nm) irradiation of proflavine in the presence of the N-oxide. In the 460nm laser pulse excitation of proflavine, furthermore, weak transient absorption due to sensitized triplet of the N-oxide was detected around 410nm.
    Journal of Photochemistry and Photobiology A Chemistry 04/2001; 140(1):27-32. DOI:10.1016/S1010-6030(01)00387-2 · 2.50 Impact Factor
  • Kunihiro Tokumura · Naoto Taniguchi · Takashi Kimura · Ryoka Matsushima
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    ABSTRACT: A photochromic behavior was found for trans-4-diethylamino-4'-dimethylamino-2-hydroxychalcone in toluene, and colored species undergoing dark reaction to regenerate trans-isomer may be ascribed to cis-isomer with the lifetime of 77 min at room temperature. It is demonstrated that a trans-->cis isomerization in the lowest triplet state is significantly responsible for the primary process of the coloration.
    Chemistry Letters 02/2001; 11(2):126-127. DOI:10.1246/cl.2001.126 · 1.23 Impact Factor
  • Ryoka Matsushima · Shuichi Fujimoto · Kunihiro Tokumura
    Bulletin of the Chemical Society of Japan 01/2001; 74(5):827-832. DOI:10.1246/bcsj.74.827 · 2.21 Impact Factor
  • Kunihiro Tokumura · Kazushige Nagaosa · Yumi Ohta · Ryoka Matsushima
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    ABSTRACT: Direct evidence for the S1→S1′ photoenolization of 3′,4′-benzo-2′-hydroxychalcone was obtained by the detection of the S1′→S0′ tautomer fluorescence spectra (λmax=600–610 nm) at 77–298K. The enol-tautomer is barely fluorescent at 298K, and the fluorescence intensity increases with decreasing temperature. The drastic increase in the S1′→S0′ fluorescence intensity with the 180→77K temperature drop demonstrates the solvent-derived viscosity barrier for the Z→E isomerization of S1′ to generate S0″ (E-enol-tautomer). Such primary photochemical processes are supported by the detection of the respective transient absorption spectra of E- and Z-enol-tautomers (S0″ and S0′) with lifetimes of 190 and 13 μs at 298K.
    Chemical Physics Letters 10/1998; 295(5):516-524. DOI:10.1016/S0009-2614(98)00984-1 · 1.90 Impact Factor
  • Yae Kumamoto · Teiko Nakatani · Kunihiro Tokumura · Michiya Itoh
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    ABSTRACT: The excimer formation and photodissociation in jet-cooled molecular clusters of 1-cyanonaphthalene (1-CNN) and its deuterated compound (1-CNN-d7) were investigated. The jet-cooled excimer fluorescence was observed in the excitation cluster band (n ≥ 4) of 1-CNN-d7 as well as of 1-CNN. The excitation of the excimer at 700−750 nm results in a considerably strong depletion of the excimer fluorescence and a simultaneous fragment fluorescence of the clusters at 335−350 nm. An excimer depletion spectrum was observed at 700−750 nm from the wavelength dependence of the depletion laser of the fragment intensity. Comparison of the excimer depletion spectrum of the jet-cooled cluster with that of the transient absorption of the excimer in solution suggests that the excitation into the upper state of the excimer induces the photodissociation of the excimer and the simultaneous fluorescence of the fragment. Fluorescence decay times of the fragment by the excimer depletion were considerably larger than those of the monomer and smaller than the dimer's. The photodissociation mechanism of the excimer was discussed in terms of decay times of the fragment fluorescence and the unexpectedly stable dimer core of 1-CNN.
    The Journal of Physical Chemistry A 07/1998; 102(32). DOI:10.1021/jp981363c · 2.69 Impact Factor
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    ABSTRACT: Time-resolved infrared absorption spectra of 7-hydroxyquinoline (7-HQ) in methanol were measured to investigate the relaxation processes following S1 → S′1 proton transfer tautomerization. Deuterium and nitrogen isotope effects were observed for the transient infrared spectra of 7-HQ-14N and -15N in MeOD and MeOH. The 1644 (1628) cm−1 band in MeOH (MeOD) is ascribed to the H(D)-bonded C = O stretching of the phototautomer in the ground state (St́0). Transient absorption decay exhibits a remarkable deuterium isotope effect. It is thus demonstrated that the ground-state reverse proton transfer of S′0 is responsible for the observed transient decay.
    Chemical Physics Letters 06/1997; 271(4-6):320-326. DOI:10.1016/S0009-2614(97)00459-4 · 1.90 Impact Factor
  • Kunihiro Tokumura · Osamu Oyama · Hiromi Mukaihata · Michiya Itoh
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    ABSTRACT: Significantly Stokes-shifted fluorescence induced by the UV photoexcitation of 2,2‘-bipyridin-3-ol in 3-methylpentane exhibits a dramatic temperature dependence such that dual fluorescence spectra (λmax = 560 and 585 nm) at room temperature are replaced by a single fluorescence spectrum (λmax = 560 nm) below 200 K. The respective emitting species responsible for the short- and long-wavelength bands may be ascribed to the excited-state primary phototautomer (S1‘) and its rotamer (S1‘‘), which is generated by the rotational isomerization of S1‘ with an activation barrier.
    The Journal of Physical Chemistry A 02/1997; 101(8). DOI:10.1021/jp962540h · 2.69 Impact Factor
  • Kunihiro Tokumura · Mutsuo Kurauchi · Nobuo Yagata · Michiya Itoh
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    ABSTRACT: Selective excitation of benzil in the presence of 3-hydroxyflavone (3HF) in fluid solution results in diffusional triplet energy transfer from benzil to 3HF, and the Tn←T1 absorption spectrum of 3HF (acceptor) was determined by transient absorption spectroscopy. It is demonstrated that red probe pulse excitation of the lowest triplet state (T1) of the normal tautomer yields green fluorescence from the phototautomer in the lowest excited singlet state (S′1). Generation of S′1 upon the excitation of T1 may be ascribed to an efficient Tn→T′n proton transfer followed by Tn′→T′2 relaxation and T′2→S′1 reverse intersystem crossing.
    Chemical Physics Letters 08/1996; 258(3):495-500. DOI:10.1016/0009-2614(96)00680-X · 1.90 Impact Factor
  • Kunihiro Tokumura · Mutsuo Kurauchi · Osamu Oyama
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    ABSTRACT: The S1′→S0′ fluorescence of 2,2′-bipyridine-3,3′-diol was detected on red probe pulse excitation of the tautomeric triplet (T1′), which was generated via S1′→S1′ double proton transfer followed by S1′→T1′ intersystem crossing. The excitation spectrum of the two-step laser-induced fluorescence corresponds satisfactorily to the transient Tn′←T1′ absorption spectrum in the 600–800 nm region. It is demonstrated that the T2′(n,π*)→S1′(π,π*) reverse intersystem crossing is responsible for the generation of S1′ on excitation of T1′. The probability of reverse intersystem crossing was estimated to be 0.0024.
    Journal of Photochemistry and Photobiology A Chemistry 08/1994; 81(3):151–158. DOI:10.1016/1010-6030(94)03794-9 · 2.50 Impact Factor
  • Kunihiro Tokumura · Nobuo Yagata · Yoshihisa Fujiwara · Michiya Itoh
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    ABSTRACT: The S1'--> S0' fluorescence spectrum (lambda(max) = 505 nm) was induced by both blue and red probe pulse excitations of transient species generated by the 308-nm pump pulse excitation of 2',3',4',5',6'-pentamethyl-3-hydroxyflavone (PM3HF) undergoing the S1 --> S1' excited-state intramolecular proton transfer in degassed 3-methylpentane at room temperature. The tautomeric lowest triplet state (T1') is predominantly responsible for the two-step laser-induced fluorescence (TSLIF) induced by red probe pulse excitation, whereas both the primary lowest triplet state (T1) and the tautomeric ground state (S0') are mainly responsible for the TSLIF induced by blue probe pulse excitation. The T2' --> S1' and the T(n) --> S(m) reverse intersystem crossings are considered as the key processes for the appearance of the S1' --> S0' fluorescence upon the excitation of T1' and T1, respectively. In addition to the S1 --> S1' excited-state proton transfer followed by the S0' --> S0 ground-state reverse proton transfer, the longer sequence, S1 --> S1' --> T1' --> S0' --> S0, was confirmed for the overall S1 --> S0 relaxation. The respective lifetimes of S1', T1', and S0' in the sequence were determined to be 1.5 ns, 20 mus, and 1.4 mus, and the lifetime of T1 was determined to be 7.5 mus. From the triplet quenching study, the T1-S0 energy gap is higher than 18 690 cm-1, and the T1'-S0' energy gap is between 11 650 and 10 900 cm-1.
    ChemInform 06/1993; 97(25). DOI:10.1021/j100127a015
  • Kunihiro Tokumura · Tomomi Ozaki · Hideyo Nosaka · Yoko Saigusa · Michiya Itoh
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    ABSTRACT: The quenching rates of the 1A2 fluorescence-state p-X-benzyls (X = F, Cl, OCH3, and OCH2ph) by molecular oxygen were determined to be (1.8-2.3) x 10(10) M-1 s-1, which are about 1 order of magnitude higher than the ground-state oxygenation rates. Physical quenching at the diffusion-limited rate and oxygenation reaction at a lower rate were demonstrated for the reactivities of the excited state (1A2) and the ground state (1B2) toward molecular oxygen, respectively. A poor quenching rate of 6.7 x 10(9) M-1 s-1 for p-cyanobenzyl in the 2B2 fluorescent state implies that the excited-state oxygenation competes with the physical quenching. The oxygenation rate of benzyl radical in the ground state (1B2) was reduced by the introduction of stabilizing substituents (Cl, phenyl, Br, NO2, and CN) at thc para position. A good correlation was found between the oxygenation rate and thc free radical substituent parameter (sigma.) based upon the NBS bromination of 4-substituted 3-cyanotoluene.
    Journal of the American Chemical Society 06/1991; 113(13). DOI:10.1021/ja00013a037 · 12.11 Impact Factor
  • Kunihiro Tokumura · Hideyo Nosaka · Yoshihisa Fujiwara
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    ABSTRACT: Transient absorption and two-step laser-induced-fluorescence measurements confirmed that the transient p-methoxybenzyl-peroxy radical generated via the oxygenation of the p-methoxybenzyl radical releases molecular oxygen upon the 308 nm pulse excitation. In the air-saturated n-hexane and cyclohexane at room temperature, the respective lifetimes of the peroxy radical were determined to be 120 and 187 μs, which are sufficiently longer than the lifetime (110–130 ns) of the p-methoxybenzyl radical. It was assumed that the peroxy radical is subjected to H-abstraction from the solvent molecule in the dark.
    Chemical Physics Letters 03/1991; 177(6):559-562. DOI:10.1016/0009-2614(91)90084-M · 1.90 Impact Factor
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    ABSTRACT: Transient absorption and two-step laser-induced fluorescence (TS-LIF) studies on the intramolecular excited-state proton transfer (ESPT) in a 3-methylpentane solution of 2-(1- and 2-naphthyl)-3-hydroxychromone (α- and β-NHC) have been reported. Transient absorption spectra of the ground (S n ← S 0) and excited states (S n ← S 1) of the tautomer generated by the ESPT in these compounds have been obtained at room temperature. The TS-LIF spectra and variable delay plots of the TS-LIF intensity as well as transient absorption (recovery) suggest that two ground-state tautomers with short and long decay times are involved in the relaxation process of the ESPT. The former and latter ground-state tautomers exhibit slightly different fluorescence spectra at λ max 538 and 515 nm in the excited state, respectively. The latter tautomer is generated in the ground state at the expense of the former and relaxes to the parent NHC molecule. Taking account of the "triplet mechanism" for TS-LIF suggested by other groups, the possible involvement of the higher triplet for the observed TS-LIF was examined. However, no significant TS-LIF signal was detected by the second laser excitation of the T-T absorption throughout 400-600 nm. The involvement of two ground-state tautomers, which was proposed here in the relaxation process of the ESPT, is discussed in terms of internal rotation of the naphthyl group at the 2 position of the γ-pyrone ring in NHC.
    ChemInform 10/1990; 22(5). DOI:10.1021/j100384a032
  • Kunihiro Tokumura · Hideyo Nosaka · Tomomi Ozaki
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    ABSTRACT: The oxygenation rate constants (kO2) of the ground-state para-substituted benzyl radicals (p-X-benzyls) were obtained by Stern-Volmer plots for the decay of the transient Dn←D0 absorption in the presence of various concentrations of dissolved molecular oxygen. A remarkable substituent effect, a sharp drop in the kO2 value in the order of p-chlorobenzyl, p-phenylbenzyl, p-bromobenzyl, p-nitrobenzyl and p-cyanobenzyl, was confirmed in contrast to almost the same kO2 values of (3.0±0.4) × 109 M−1 s−1 for p-X-benzyls (X = H, CH3, OCH3 and F).
    Chemical Physics Letters 06/1990; 169(4):321-325. DOI:10.1016/0009-2614(90)85210-4 · 1.90 Impact Factor
  • Kunihiro Tokumura · Fumie Kiso · Mitsue Dohi · Nobuyuki Takamichi · Michiya Itoh
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    ABSTRACT: Unusually long-lived (500 ns) doublet-doublet fluorescence of p-methoxybenzyl radical was observed in the KrF-laser photolysis of p-methylanisole in hexane at room temperature, in spite of the intrinsic fluorescence lifetime (120 ns) of the radical. It was confirmed that the triplet-doublet electronic energy transfer from p-methylanisole to p-methoxybenzyl is responsible for the long-lived fluorescence. The rate constant of the energy transfer was determined to be 1.2×1010M−1s−1.
    Chemical Physics Letters 11/1989; 163(6):509-513. DOI:10.1016/0009-2614(89)85178-4 · 1.90 Impact Factor
  • Kunihiro Tokumura · Tomomi Ozaki · Michiya Itoh
    Journal of the American Chemical Society 08/1989; 111(16). DOI:10.1021/ja00198a004 · 12.11 Impact Factor