Country：Japan

DOI： 10.5702/massspec.s22-05

DOI： 10.1021/acs.jpca.1c06390

DOI： 10.1016/j.chemphys.2020.110817

DOI： 10.1016/j.chemphys.2020.110817

DOI： 10.1016/j.cplett.2020.137570

DOI： 10.1016/j.cplett.2020.137570

DOI： 10.1016/j.cplett.2020.137504

DOI： 10.1016/j.cplett.2020.137504

DOI： 10.1002/cphc.202000021

DOI： 10.1002/cphc.202000021

DOI： 10.1002/cphc.202000282

<p>Synthesis of iron oxide nanoparticles (Fe-O NPs) from iron(III)acetylacetonate solution by femtosecond laser irradiation is reported. Fe-O NPs and carbon are agglomerated in <i>n</i>-hexane, while single-nanometer-sized dispersed Fe-O NPs are obtained in water. We propose that the choice of ligands and solvent determines the primary particle size distribution and dispersion states of NPs as well as carbon contaminants in laser-assisted synthesis using metal complexes as reactants.</p>

DOI： 10.1246/cl.190751

CiNii Article

<p>Synthesis of iron oxide nanoparticles (Fe-O NPs) from iron(III)acetylacetonate solution by femtosecond laser irradiation is reported. Fe-O NPs and carbon are agglomerated in <i>n</i>-hexane, while single-nanometer-sized dispersed Fe-O NPs are obtained in water. We propose that the choice of ligands and solvent determines the primary particle size distribution and dispersion states of NPs as well as carbon contaminants in laser-assisted synthesis using metal complexes as reactants.</p>

DOI： 10.1246/cl.190751

CiNii Article

DOI： 10.1016/j.ijms.2019.116236

DOI： 10.1016/j.ijms.2019.116236

DOI： 10.32163/amadareport.33.0_349

CiNii Article

<p>We report the production of the long-lived hexafluorobenzene tetracation, which is the smallest aromatic tetracation ever investigated, by 0.8 µm femtosecond laser pulses. The yield of tetracation relative to trication radical is 0.11. Using the time-of-flight mass spectrometer equipped with the fast ion gate and the curved field reflectron, we estimate the lower limit of the lifetime of tetracation to be 9 µs. Confinement of multiple positive charges in a small organic molecule is unexpected; however, our finding is an answer of this fundamental concern.</p>

DOI： 10.1246/cl.190667

CiNii Article

芳香族フッ素化合物にフェムト秒レーザーを照射することで、芳香族化合物では最も小さい4価陽イオン（ヘキサフルオロベンゼン、C6F6）を生成することに成功しました。イオンの検出には飛行時間型質量分析計を用い、イオンの飛行時間からイオンのm/zを決定しました。さらに、同位体ピークの面積比から元素組成を決定しました。このような多価陽イオンを生成することができた理由として、フェムト秒レーザーを用いるトンネルイオン化によって生じるイオンが余剰なエネルギーをもたないこと、プロトンとして容易に脱離する水素原子をフッ素原子で置換したことが挙げられます。今回、フェムト秒レーザーを用いることで芳香族4価陽イオンについて分子サイズの最小値を34年ぶりに更新しました。その一方で、リフレクトロンを用いて、4価ヘキサフルオロベンゼンの寿命の下限値を9マイクロ秒と見積もりました。ヘキサフルオロベンゼンについては、高速イオン選別器を用いて価数別にイオンを選別し、解離で生じる生成物をリフレクトロンによって分離する事で価数ごとの反応の観測を試みました。しかしながら、検出感度を限界まで上げても生成物は観測されませんでした。多価陽イオンが単独では極めて安定であることが明らかになりましたので、これまで未知であった多価陽イオンの物性や反応の研究が可能であるといえます。また、多価陽イオンのサイズが十分に小さくなったため理論研究にも取り組みやくなったといえます。これらの課題については、引き続き研究を進めていくつもりです。(参照: LINＫ1)

DOI： 10.1246/cl.190667

CiNii Article

DOI： 10.1016/j.chemphys.2019.110465

DOI： 10.1016/j.chemphys.2019.110465

DOI： 10.1021/acs.langmuir.9b01854

DOI： 10.1021/acs.langmuir.9b01854

DOI： 10.1016/j.jphotochem.2018.10.009

DOI： 10.1016/j.jphotochem.2018.10.009

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Iron-based nanoparticles (FeNPs) have unique and attractive properties such as superparamagnetism, biocompatibility, and catalytic activity. Although the synthesis of precious metal NPs from a metal in liquid and/or metal salt solution by a pulsed laser has been investigated, comparably little effort has been devoted to examine the production of FeNPs. Here we report the synthesis of carbon-shell free spherical NPs of iron oxide (magnetite) from ferrocene hexane solution by femtosecond near infrared laser pulses. Nanosecond UV laser pulses are used to compare the evolution of the particle size distribution as a function of laser irradiation time. The size of NPs remains constant even for extended exposure to femtosecond laser pulses, whereas it grows with exposure to nanosecond laser pulses. The primary particles are generated by photochemical reactions regardless of pulse duration; however, the fragmentation of NPs by successive femtosecond laser pulses regulates the particle size.

DOI： 10.1002/cphc.201800436

PubMed

DOI： 10.1002/cphc.201800436

Other URL： http://orcid.org/0000-0002-6810-7774

DOI： 10.1016/j.jphotochem.2018.06.006

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2018 Elsevier B.V. The kinetic energy of ions produced by a Coulomb explosion, in which multiply charged molecular cations dissociate, is determined by the charge number, mass, and geometric configuration of the ions upon explosion. Although the importance of the structural deformation and migration of atoms on kinetic energy variations is well known, there has been little investigation into the effect of charge localization before the ions are released. In this study, the angular distributions of iodine and carbon ions ejected from linear alkanes, which have one iodine atom on each side of an alkyl chain having one to six carbon atoms, are measured. The highly charged iodine ions (I4+, I5+) are emitted mostly along the laser polarization direction, whereas the angular distribution of iodine ions becomes isotropic the longer the alkyl chain and the lower the charge number of iodines are. Furthermore, the longer the alkyl chain, the higher the kinetic energy of iodine and carbon ions. The emission of ions is discussed in terms of the selective ionization of aligned molecules based on their molecular orbitals. The charge localization during ionization in strong alternating electric fields followed by two-body Coulomb explosion via a C–I bond cleavage is proposed.

DOI： 10.1016/j.jphotochem.2018.06.006

DOI： 10.1246/cl.180379

CiNii Article

Authorship：Lead author,　Corresponding author  

© 2017 Elsevier B.V. Intense femtosecond lasers as well as X-ray free electron lasers provide new means to produce multiply charged molecular cations. The fragmentation processes that these high energy species undergo, termed Coulomb explosion, are utilized to determine the static molecular structures as well as to trace the molecular dynamics of ultrafast chemical reactions. This review focuses on recent advances made in studies of Coulomb explosion imaging, highlighting the use of this process to determine the static structures of complex molecules, geometric isomers, chiral molecules and molecular complexes. Briefly, we summarize the recent time-resolved studies of surface electric fields and the controversy pertaining to the contribution of Coulomb explosion to the mechanism for ablation of solid surfaces.

DOI： 10.1016/j.jphotochemrev.2017.12.001

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2018 The Chemical Society of Japan. A sub-nanosecond visible laser coupled with a liquid chromatograph is utilized for atmospheric pressure laser ionization (APLI). We reveal that the range of applicable substances for nonresonant three-photon ionization is determined by the proton affinity and the ionization potential, the latter of which is lowered by solvation with eluents. APLI with a visible laser can be used for fragmentation- and background-free detection of analytes as well as to investigate the ionization threshold of solvated molecules.

DOI： 10.1246/cl.180379

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cphc.201700381

Other URL： http://orcid.org/0000-0002-6810-7774

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The inclusion of an ion gate in a tandem mass spectrometer allows a specific precursor ion to be selected, and the fragment ions are then used for structure analysis and to investigate chemical reactions. However, the performance of an ion gate has been judged simply by whether or not the target ion was selected. In this study, we designed, manufactured, constructed, and characterized a Bradbury–Nielsen ion gate (BNG). The actual ion selection ability, i.e. the gate function, of the BNG was measured for isotopes of Xez+ (z=1–6). The gate function of the BNG was 36.5±0.5 ns in width and 3–13 ns in rise and fall times. The BNG provides a simple way to select multiply charged molecular cations of small organic molecules as well as large molecules such as proteins and peptides.

DOI： 10.1002/cphc.201700381

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cphc.201700802

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jphotochem.2017.05.011

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2017 Elsevier B.V. We report on the transformation of dichloromethane to low-chlorine carbon nanoparticles by the exposure of aqueous dichloromethane solution and/or dichloromethane/water biphasic solution to femtosecond laser pulses. The pH of either solution immediately decreased due to the reduction of dichloromethane by hydrated electrons. The time evolution of transmittance revealed that particle formation was suppressed when the initial pH was low because protons scavenge hydrated electrons. The size and morphology of nanoparticles was independent of the initial pH and the reaction solution used. The analysis of the elemental composition of carbon particles showed that the Cl/C atomic ratio was, independent on the initial pH values, greatly reduced to 0.06. We propose that the violent destruction of dichloromethane and elimination of chlorine atoms not only as Cl− but also Cl2 excludes chlorine atoms from the carbon network construction processes toward the formation of carbon nanoparticles.

DOI： 10.1016/j.jphotochem.2017.05.011

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cphc.201600602

Other URL： http://orcid.org/0000-0002-6810-7774

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim We report on the preparation and characterization of fluorine-doped hydrophilic carbon nanoparticles by the exposure of hexafluorobenzene or a water/hexafluorobenzene bilayer solution to femtosecond laser pulses. Uniform atom distributions are achieved not only on the particle surface but also inside the particles. The semi-ionic character of C−F bonds and the non-aggregating feature of the nanoparticles play key roles in the water-dispersible character of fluorine-doped carbon nanoparticles. We suggest the following building-up process of carbon nanoparticles: the fragmentation of hexafluorobenzene initiated by the electrons generated in laser-induced plasma followed by the reconstruction of a carbon framework of nanoparticles.

DOI： 10.1002/cphc.201600602

PubMed

Kind of work：Single Work  

We briefly review femtosecond laser induced chemical reactions and nanomaterial productions in aliquid phase. Focused intense femtosecond laser pulses create a high density of reactive species such assolvated electrons and cation radicals of the solvent. The solvated electrons efficiently reduce the metalions followed by their nanoparticle formations. Multimetallic nanoparticles, which are expected to beutilized as electromagnetic materials and catalysts, are produced. In the cases of neat organic solvents,polyynes and carbon nanoparticles are formed. We also presented the production of heteroatom-dopedcarbon nanoparticles, which are candidates of oxygen reduction catalysts in fuel cells. By using aqueousorganic solutions and/or water/organic bilayer solutions, hydrophilic carbon nanoparticles are formed bythe successive oxidation of organic molecules by hydroxyl radicals. Nanoparticle synthesis by reactivespecies in the liquid phase might be an alternative means of widely used laser ablation in liquid.

DOI： 10.2184/lsj.45.5_278

CiNii Article

We briefly review femtosecond laser induced chemical reactions and nanomaterial productions in a
liquid phase. Focused intense femtosecond laser pulses create a high density of reactive species such as
solvated electrons and cation radicals of the solvent. The solvated electrons efficiently reduce the metal
ions followed by their nanoparticle formations. Multimetallic nanoparticles, which are expected to be
utilized as electromagnetic materials and catalysts, are produced. In the cases of neat organic solvents,
polyynes and carbon nanoparticles are formed. We also presented the production of heteroatom-doped
carbon nanoparticles, which are candidates of oxygen reduction catalysts in fuel cells. By using aqueous
organic solutions and/or water/organic bilayer solutions, hydrophilic carbon nanoparticles are formed by
the successive oxidation of organic molecules by hydroxyl radicals. Nanoparticle synthesis by reactive
species in the liquid phase might be an alternative means of widely used laser ablation in liquid.

DOI： 10.2184/lsj.45.5_278

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cphc.201600555

Other URL： http://orcid.org/0000-0002-6810-7774

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Several features distinguish intact multiply charged molecular cations (MMCs) from other species such as monocations and polycations: high potential energy, high electron affinity, a high density of electronic states with various spin multiplicities, and charge-dependent reactions. However, repulsive Coulombic interactions make MMCs quite unstable, and hence small organic MMCs are currently not readily available. Herein, we report that the isolated four-atom molecule diiodoacetylene survives after the removal of four electrons via tunneling. We show that the tetracation remains metastable towards dissociation because of the localization (91–95 %) of the positive charges on the terminal iodine atoms, ensuring minimum Coulomb repulsion between adjacent atoms as well as maximum charge-induced attractive dipole interactions between iodine and carbon. Our approach making use of iodines as the positively charged sites enables small organic MMCs to remain intact.

DOI： 10.1002/cphc.201600555

Publishing type：Research paper (scientific journal)  

© 2016 Wiley Periodicals, Inc. The decomposition of aqueous chlorohydrocarbons regarded as environmental pollutants has been widely studied. However, it is usually difficult to separate liquid and/or volatile products originated from chlorohydrocarbons from reactant solution. We succeeded to precipitate hydrophobic carbon nanoparticles and their agglomerates from aqueous dichloromethane by femtosecond laser (0.8 μm, 40 fs) irradiation. In the case of water/dichloromethane bilayer solution, the precipitates were produced in abundance when the water layer was exposed to femtosecond laser pulses. The time evolution of pH and transmittance revealed that the precipitation of carbon particles was preceded by dechlorination. Focusing intense femtosecond laser pulses onto water creates a high density of reactive species in a well-confined volume; that is, plasma filament. The graphitization hence solidification by using laser pulses could be a useful way to remove chlorinated compounds from their aqueous solution.

DOI： 10.1002/ecj.11873

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/ecj.11873

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpca.6b05113

Publishing type：Research paper (scientific journal)  

© 2016 American Chemical Society. Multiple ionization and subsequent Coulomb explosion have been studied for many organic molecules and their clusters; however, the metal complexes, particularly the large Coulombic interactions expected between a metal and its ligands, have not yet been explored. In this study, the angular distribution of CO+, oxygen, and carbon ions ejected from metal hexacarbonyls (M(CO)6, M: Cr, Mo, W) having Oh symmetry by Coulomb explosion in femtosecond laser fields (>1 × 1014 W cm-2) is investigated. The emissions of oxygen ions are well-explained in terms of the geometric alignment along a line inclined 45° relative to the CO-M-CO axis in a M(CO)4 plane. Unlike the explosion behavior of the oxygen ions located on the outer part of the molecule, the explosion behavior of the carbon ions was affected by the laser intensity, kinetic energy, and metal. This finding that the emission trends of carbon sandwiched between oxygen and metal atoms were the opposite of those for oxygen was explained by the obstruction by oxygen, the deformation of structure in bending coordinates, and the strong interaction with charged metal. The anisotropic Coulomb explosion of metal complexes reflecting their structural symmetry and central metal charge is a promising candidate for use in the investigation of large Coulombic interactions at the molecular level.

DOI： 10.1021/acs.jpca.6b05113

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijms.2016.03.011

Publishing type：Research paper (scientific journal)  

© 2016 Elsevier B.V. We investigated the significant differences in the angular distribution of carbon ions ejected from dimethylacetylenes (CH3-CC-CH3 and CH3-CC-CC-CH3) and diiodoacetylenes (I-CC-I and I-CC-CC-I) induced by a Coulomb explosion. The longest linear chain molecule ever reported was exposed to intense femtosecond laser fields (40 fs, <5 × 1014 Wcm-2) in this study. In the cases of the diiodoacetylenes, the angular distributions of the carbon ions were orthogonal with respect to the laser polarization direction and became narrower as the length of the molecules became longer. This is in sharp contrast to the dimethylacetylenes, in which the angular distributions of the carbon ions were parallel with respect to the laser polarization direction and became broader as the length of the molecules became longer. The specific angular distributions of carbon ions ejected from the diiodoacetylenes are explained in terms of the frozen molecular rotation, the blocking of carbon ion emission, and the bending of carbon chains at highly charged states due to the presence of iodines.

DOI： 10.1016/j.ijms.2016.03.011

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jphotochem.2015.12.021

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

© 2016 Elsevier B.V. All rights reserved. Chemical reactions of metal ions in solution were studied using 800 nm, 90 femtosecond laser pulses with a laser intensity range beginning at sub-micro-Joules/pulse, where the intensities were at or just below supercontinuum generation. Products were observed as surface resonance absorptions assignable to Ag, Au nanoparticles (NPs) and light scattering, indicating the formation of Pd NPs. The consumption efficiencies of metal ions from the Au and Pd ions were estimated to be 10-3 per incident photon. The major absorbing species of the laser energy was water, which led to the formation of solvated electrons that acted as a reducing agent of metal ions, while direct multi-photon dissociation to neutral atoms was unlikely. Metal ion Fe3+and Yb3+ systems are also discussed, where Fe3+ to Fe2+ was ascribed to two-photon absorption and Yb3+ to Yb2+ to a reduction followed by solvent ionization.

DOI： 10.1016/j.jphotochem.2015.12.021

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

DOI： 10.1246/bcsj.20140247

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

The decomposition of aqueous chlorohydrocarbons regarded as environmental pollutants has been widely studied. However, it is usually difficult to separate liquid and/or volatile products originated from chlorohydrocarbons from reactant solution. We succeeded to precipitate hydrophobic carbon nanoparticles and their agglomerates from aqueous dichloromethane by femtosecond laser (0.8 µm, 40 fs) irradiation. In the case of water/dichloromethane bilayer solution, the precipitates were produced in abundance when the water layer was exposed to femtosecond laser pulses. The time evolution of pH and transmittance revealed that the precipitation of carbon particles was preceded by dechlorination. Focusing intense femtosecond laser pulses onto water creates a high density of reactive species in a well-confined volume; i.e., plasma filament. The graphitization hence solidification by using laser pulses could be an useful way to remove chlorinated compounds from their aqueous solution.

DOI： 10.1541/ieejeiss.135.1075

CiNii Article

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

© 2014 The Chemical Society of Japan. We synthesized hydrophilic and hydrophobic carbon nanoparticles (CNPs) by femtosecond laser (0.8 μm, 40 fs) irradiation of the water layer of an aerated benzene/water (B/W) bilayer solution. Focusing intense femtosecond laser pulses onto water creates a high density of reactive species such as hydroxyl radicals in a well-confined volume; i.e., plasma filament. The properties of the particle surface were controlled simply by adjusting the laser focusing position, the duration between the preparation of B/W bilayer solution and the laser irradiation. The hydrophobic CNPs appeared to be nearly identical in size and morphology to hydrophilic CNPs. Raman spectroscopy revealed that both particles had a graphitic and disordered structure; however, IR spectroscopy clearly showed that the hydroxy group is the origin of the hydrophilicity. The time evolution of particle formation, products in water, and benzene dissolution behavior in water reveals that the surface properties are determined by the concentration of benzene in water. The diluted aqueous benzene solution gave hydrophilic particles; however, the density of particles was much smaller than that formed in B/W bilayer solution. We concluded that the production of denser hydrophilic CNPs in B/W bilayer was achieved by limiting the concentration of benzene in water layer by B/W interface, and by continuously supplying benzene into water layer through B/W interface. We discuss the subsequent reaction mechanism leading to CNPs of different surface characters.

DOI： 10.1246/bcsj.20140247

CiNii Article

Publishing type：Research paper (scientific journal)  

© 2015 The Institute of Electrical Engineers of Japan. The decomposition of aqueous chlorohydrocarbons regarded as environmental pollutants has been widely studied. However, it is usually difficult to separate liquid and/or volatile products originated from chlorohydrocarbons from reactant solution. We succeeded to precipitate hydrophobic carbon nanoparticles and their agglomerates from aqueous dichloromethane by femtosecond laser (0.8 μm, 40 fs) irradiation. In the case of water/dichloromethane bilayer solution, the precipitates were produced in abundance when the water layer was exposed to femtosecond laser pulses. The time evolution of pH and transmittance revealed that the precipitation of carbon particles was preceded by dechlorination. Focusing intense femtosecond laser pulses onto water creates a high density of reactive species in a well-confined volume; i.e., plasma filament. The graphitization hence solidification by using laser pulses could be an useful way to remove chlorinated compounds from their aqueous solution.

DOI： 10.1541/ieejeiss.135.1075

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.6122/CJP.52.504

Publishing type：Research paper (scientific journal)  

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp402194g

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Ytterbium 3+ ions in alcohol were found to be reduced to the corresponding 2+ ions upon laser irradiation with a stepwise two-color two-photon excitation. The infrared (975-nm) pulse with a duration of 4 ns pumps the ground state to the 4f excited state with the transition of 2F5/2 ← 2F7/2, and the second photon (355-nm) generates the charge transfer (CT) state of Cl 3p to Yb 4f; the reduction then occurs. Laser energy and excitation wavelength dependencies well-explain the above mechanism. The product Yb2+ was detected by its absorption spectrum peak at 367 nm. The absorption spectrum of the intermediate in the two-photon chemistry was measured from the 4f excited state (2F5/2) to the CT state by nanosecond laser photolysis. The intermediate spectrum appears in the wavelengths shorter than 400 nm with the molar extinction coefficient on the order of (102 M-1 cm-1) at 340 nm and can be explained in terms of the CT absorption shifted by IR photon energy. A UV nanosecond laser pulse (266 nm from a YAG laser with a duration of 6 ns) can generate the reactive CT state by one-photon absorption and leads to Yb 2+ formation. The reaction yields for single-photon UV excitation and the second photon in the two-photon excitation are on the order of 0.1, suggesting that the reactive states are a common CT state. © 2013 American Chemical Society.

DOI： 10.1021/jp402194g

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp310361x

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Strikingly different Coulomb explosion behavior under intense laser fields is shown between the cis and trans geometric isomers of dichloroethene using 40-fs pulses at 0.8 μm. Although the fragment-ion distributions in the mass spectra did not aid in the identification of the geometric and positional isomers of the dichloroethenes, we found that the angular distributions of atomic ions were strongly dependent on the geometric structures. The angular distributions of chlorine ions, carbon ions, and protons were similar between 1,1- and cis-1,2-dichloroethene, whereas trans-1,2-dichloroethene showed a very sharp distribution of chlorine ions and quite different distributions of carbon ions and protons. The origin of the anisotropic ion angular distributions is the geometric selection of molecules in the tunnel-ionization process followed by a Coulomb explosion, although molecules are randomly oriented in the gas phase. The highly charged molecular ions exploded into pieces, and the direction of atomic-ion ejection was strongly correlated with the relative configuration of atoms with respect to the electron-extraction axis, the repulsion with adjacent atomic ions within the molecule, and the degree of the persistence of a molecular frame. We propose herein that the most probable electron-extraction axis by tunneling, which is governed by the configuration of molecular orbitals, is different among three dichloroethene isomers. Because multiple ionization under intense laser fields occurs by sequential tunneling processes, the first ionization step at the leading edge of the laser pulse dominates the further ionization steps. Therefore, the shapes of the highest occupied molecular orbitals and probably the underlying orbitals determine the anisotropic emission of atomic ions that can be used to identify isomers. © 2013 American Chemical Society.

DOI： 10.1021/jp310361x

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.2012.722

CiNii Article

Other URL： http://orcid.org/0000-0002-6810-7774

CiNii Article

Publishing type：Research paper (scientific journal)  

The irradiation of NIR femtosecond laser pulses to a benzene/water bilayer dramatically enhanced the formation of carbon nanoparticles compared with that in neat benzene. The focusing-position-dependent chemistry and the oxidative mechanism of nanoparticle formation are discussed. © 2012 The Chemical Society of Japan.

DOI： 10.1246/cl.2012.722

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jphotochem.2011.02.031

Publishing type：Research paper (scientific journal)  

While studying a series of methyl-substituted benzenes, C6H 6-n(CH3)n with n = 2, 3, 4, 6, and perfluorobenzene in the gas phase using 193-nm laser flash photolysis, we observed the formation of p-xylylene (benzoquinodimethane) due to the elimination of two hydrogen atoms as a result of a two-photon process. The results were explained in terms of an intermediate hot molecule formed by internal conversion which finally led to the ground electronic state. Quadratical dependencies on the photoproducts were observed for toluene, xylene, mesitylene, and perfluorobenzene in the presence of a foreign gas, while linear dependencies were observed for durene and hexamethylbenzene. Dewar-type benzene was detected from photolysis of hexamethylbenzene. © 2011 Elsevier B.V.

DOI： 10.1016/j.jphotochem.2011.02.031

Publishing type：Research paper (scientific journal)  

Multiply charged iron atoms up to Fe6+ with few carbon ions were produced from ferrocene under intense femtosecond laser fields. The production of Fe4+ and Fe5+ from ferrocene requires much less laser intensity than theoretically expected for iron atoms. The dissociation of ferrocene and the generation mechanism of multiply charged iron atoms are discussed. © 2011 the Societies Owner.

DOI： 10.1039/c0cp02122a

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cphc.201000756

Publishing type：Research paper (scientific journal)  

Multiply charged carbons from diiodoacetylene are emitted orthogonally to the laser polarization direction with significant energy, whereas those from acetylene were emitted parallel to the laser polarization direction (see scheme). The distinct carbon emissions from diiodoacetylene can be explained in terms of the persistence of a molecular frame at a high charge state, and the deformation within the Coulomb field formed by the two adjacent iodine ions. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/cphc.201000756

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c0cp02122a

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp1067186

Publishing type：Research paper (scientific journal)  

Quadruply charged, neon-like silicon and helium-like carbon were generated by the exposure of hexamethyldisilane to intense femtosecond laser pulses. Dissociation of the silicon?silicon bond, the formation of highly charged silicons, as well as the saturation intensity of their formation were studied by mass spectroscopy. The production of these ions in high abundance, but also with lower laser intensity than theoretically expected for the element, was accomplished by using organosilicon compounds. Multiply charged silicon was generated at low laser intensity because stripping electrons from organosilicon compounds is much easier than from pure silicon due to the loose binding of electrons belonging to molecular orbitals. Femtosecond laser ionization is a valuable methodology for producing highly charged ions in high abundance and is useful in many fields of interest. © 2010 American Chemical Society.

DOI： 10.1021/jp1067186

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp1041475

Publishing type：Research paper (scientific journal)  

The photocycloreversion of anthracene photodimers and biplanemer in solution was investigated by nonresonant intense femtosecond laser pulses. Cycloreversion of biplanemer showed a pseudolinear response to laser intensity whereas the formation of anthracene from photodimer was proportional to the cubic of laser intensity. The unusual intensity dependence of biplanemer was explained in terms of the sum of three-photon intramolecular cycloreversion and the recovery of reactant by a two-photon intramolecular cyclodimerization. The coexistence of high- and low-order multiphoton processes within the same laser pulse originated in the spatial distribution of the laser intensity. We observed white light emerging from the sample solution; however, the effect of solvated electrons was not observed in the present system. The saturation of both the photoreaction and white light due to a volume effect was observed at high intensity. © 2010 American Chemical Society.

DOI： 10.1021/jp1041475

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp103725s

Publishing type：Research paper (scientific journal)  

We investigated the formation and fragmentation of multiply charged molecular ions of several aromatic molecules by intense nonresonant femtosecond laser pulses of 1.4 -m with a 130 fs pulse duration (up to 2 × 10 14 W cm-2). Quadruply charged states were produced for 2,3-benzofluorene and triphenylene molecular ion in large abundance, whereas naphthalene and 1,1α-binaphthyl resulted only in up to triply charged molecular ions. The laser wavelength was nonresonant with regard to the electronic transitions of the neutral molecules, and the degree of fragmentation was strongly correlated with the absorption of the singly charged cation radical. Little fragmentation was observed for naphthalene (off-resonant with cation), whereas heavy fragmentation was observed in the case of 1,1α-binaphthyl (resonant with cation). The degree of H2 (2H) and 2H2 (4H) elimination from molecular ions increased as the charge states increased in all the molecules examined. A striking difference was found between triply and quadruply charged 2,3-benzofluorene: significant suppression of molecular ions with loss of odd number of hydrogen was observed in the quadruply charged ions. The Coulomb explosion of protons in the quadruply charged state and succeeding fragmentation resulted in the formation of triply charged molecular ions with an odd number of hydrogens. The hydrogen elimination mechanism in the highly charged state is discussed. © 2010 American Chemical Society.

DOI： 10.1021/jp103725s

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp9109089

Publishing type：Research paper (scientific journal)  

Samarium 3+ ions in methanol were found to be reduced to the corresponding 2+ ions upon irradiation with intense femtosecond laser pulses. The reduction was observed at both pulses with central wavelengths of 403 nm converted from an 800 fs fundamental pulse and 800 nm with a duration of 43 fs. When the laser wavelength was tuned to the 4f-4f absorption at 403 nm corresponding to the 6P3/2 ← 6H5/2 transition, the reduction occurred by multiphoton absorption, presumably due to reaching the deep charge transfer state. In the case of excitation by 800 nm pulses of the fundamental wavelength of the Ti:sapphire laser, the reduction is considered to occur via solvent ionization followed by electron capture by Sm3+. The product Sm2+ was detected by its fluorescence, which was observed for the first time in solution and showed a broad spectrum peak around 750 nm with a quantum yield of 0.050 in methanol in the presence of 15-crown-5-ether. © 2010 American Chemical Society.

DOI： 10.1021/jp9109089

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp902557v

Publishing type：Research paper (scientific journal)  

Ionization and fragmentation were studied on alkylphenols with long alkyl chains (p-(C6H4)(OH)(CnH2n-1), n = 1,3,5,8,9) and, for reference, on alkylbenzenes ((C6H 5)(CnH2n-1), n = 1,3,5,7,9) by intense femtosecond laser pulses, typically with 43 fs duration at 0.8 μm and 140 fs at 1.3 μm in an intensity range of 1014 W cm-2. The major products were the corresponding molecular and C7 fragment ions from the alkylphenols and alkylbenzenes. The molecular ion yields decreased from nearly 1 (n = 1) to 0.3-0.5 (n = 9) when the carbon number in the alkyl chain increased for both excitation wavelengths. Higher yields of the molecular ions were observed at a longer wavelength of 1.3 μm. The long wavelengths in the range of 1.3-1.5 μm were used to determine whether or not -OH absorption had any increase in fragment ions. No effect was observed by vibrational overtone excitation of the -OH group in this wavelength range. Direct dissociation by cation absorption is the most plausible explanation of the present fragmentation results. Other possible mechanisms were discussed, including a statistical model, an effect of electron rescattering, a multiactive electron model, and dissociation from the superexcited state. In the case of cyclohexane, nonresonant wavelength excitation with a pulse of 1.3 μm (150 fs) effectively suppressed fragmentation more than excitation by a resonant but short-duration pulse (0.8 μm, 15 fs). © 2009 American Chemical Society.

DOI： 10.1021/jp902557v

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp8082985

Publishing type：Research paper (scientific journal)  

Fused anthracene cation and a series of anthracene-CnH m cluster-like products were observed on irradiation with nonresonant femtosecond pulses at 1.4 m. Ionization of polycrystalline anthracene revealed strikingly different features such as the absence of multiply charged molecular ions, the appearance of H+ and C+ at low intensity without the formation of CnHm fragment ions, CnH m-attached and detached molecular ions, and multimer cation formation, compared with the gas-phase experiments. The fusion reactions of anthracene and CnHm fragments indicated the presence of novel reactions among high-density cations in the crystal produced by femtosecond laser irradiation. © 2009 American Chemical Society.

DOI： 10.1021/jp8082985

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

DOI： 10.1109/CLEOPR.2009.5292380

Other URL： http://orcid.org/0000-0002-6810-7774

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (international conference proceedings)  

Molecular ions of alkylphenols and cyclohexane were found to be produced more effectively with longer wavelength excitation. The cation resonance would enhance the fragmentation in femtosecond ionization of the organic molecules. © 2009 IEEE.

DOI： 10.1109/CLEOPR.2009.5292380

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ja806488n

Publishing type：Research paper (scientific journal)  

The five and possibly seven-photon fluorescence was observed for organic molecules in solution for the first time. A high-intensity laser enabled us to measure the properties of the high and any-order processes, and the emission could be directly visualized by the eye. These results showed that the common two-photon microscope could be upgraded to the higher order multiphoton microscope by choosing suitable excitation wavelengths. The multiphoton absorption cross sections differed by a factor of 1033 as the order of the multiphoton process increased. Copyright © 2008 American Chemical Society.

DOI： 10.1021/ja806488n

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cplett.2008.10.005

Publishing type：Research paper (scientific journal)  

Europium 3+ ions in methanol were found to be reduced to the corresponding 2+ ions upon irradiation with intense femtosecond laser pulses. The excitation wavelength of 800 nm was nonresonant with their electronic transitions of Eu3+. It is notable that femtosecond white-light laser was generated when the reactions occurred. The mechanisms can be explained in terms of solvated electron formation followed by the reduction. The electron ejection in a focused beam in solution has been known to be accompanied by white-light laser. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2008.10.005

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp8023028

Publishing type：Research paper (scientific journal)  

Desorption of C60+ and its dimer cation was investigated on irradiation with nonresonant femtosecond laser pulses at 1.4 μm. Ionization of solid C60 revealed strikingly different features, such as the absence of multiply charged molecular ions, the emission of C+ at low laser intensity, C2 attachments, delayed ionization, and dimer cation formation, as compared with the gas phase experiments. The large kinetic energy distribution of ions found in this study indicated that the desorption process was mainly driven by an electrostatic mechanism rather than by thermal, photochemical, or volume expansion mechanisms. Singly charged C60 emission by a Coulomb explosion due to the high density of C60+ is suggested. © 2008 American Chemical Society.

DOI： 10.1021/jp8023028

PubMed

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.50847/collision.05.r002

Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.2764078

Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.2738468

Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.2713107

DOI： 10.1007/978-3-540-38156-3-2

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

DOI： 10.1039/b611877a

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

The authors investigated Coulomb explosions of ethynylbenzenes under intense femtosecond laser fields. Deuteration on the edge of the triple bond gave information about specific fragment emissions and the contribution of hydrogen migration. Some fragments not resulting from migration were emitted in the direction of laser polarization. These were ethynyl fragment ions (D+, C D+, C2 D+, and C3 D+). Although two bonds have to be cleaved to produce C3 D+, the rigid character of the triple bond was maintained in the Coulomb explosion process. In contrast, fragment ions, which are formed after single or double hydrogen migration, showed isotropic emissions with distinct kinetic energies. The character of the substituents has been found to hold even under strong laser light fields where violent fragmentation took place. The ethynyl parts were emitted like bullets from the molecular frame of ethynylbenzene despite the explosion into pieces of the main body of benzene ring. © 2007 American Institute of Physics.

DOI： 10.1063/1.2738468

Publishing type：Research paper (scientific journal)  

The authors compared circularly and linearly polarized lights in the ionization and fragmentation of anthracene, using 800 nm femtosecond laser pulses at intensities of 1013 - 1015 W cm-2. Singly and doubly charged intact molecular ions as well as numerous fragment ions were observed in the mass spectra, which were investigated as a function of laser intensity and polarization. At comparable intensities above the saturation threshold for complete ionization, the fragmentation pathways are enhanced with a circularly polarized field compared to a linearly polarized field. Resonant excitation of the molecular cation through the Au2 Bg2 transition is proposed to be the initial step to ion fragmentation. The circularly polarized field interacts with a larger fraction of the randomly oriented molecules than the linearly polarized field, and this is considered to be the reason for the enhanced fragmentation brought about by circularly polarized light. © 2007 American Institute of Physics.

DOI： 10.1063/1.2713107

Publishing type：Research paper (scientific journal)  

Methane derivatives of C H3 -X (X: H, F, Cl, Br, I, and CN) were ionized and fragmented by an intense femtosecond laser with a 40 fs pulse at 0.8 μm in intensities of 1013 - 1015 W cm-2. The curves of the ionization yields of C H3 -X versus laser intensities have been found to be fitted with an atomic ionization theory (the theory of Perelomov, Popov, and Terent'ev) that has been established to reproduce experimental results well for rare gas atoms. The saturation intensities have been reproduced within a factor of 1.6 of the calculated ones. For molecules with low ionization potentials such as amines, another atomic ionization theory (the theory of Ammosov, Delone, and Krainov) reproduced the saturation intensities. The atomiclike ionization behavior of molecules indicates that the fragmentation occurs after the ionization. The fragmentation mechanisms after the ionization of some molecular ions are discussed. © 2007 American Institute of Physics.

DOI： 10.1063/1.2764078

Publishing type：Research paper (international conference proceedings)  

Ionization of organic molecules irradiated with intense infrared femtosecond pulses is explained from the perspective of intact molecular ion formation. Although fragmentation is more suppressed in general by femtosecond pulse excitation than pico- and nanosecond pulse excitations, molecules are still often heavily fragmented. Among the excitation parameters affecting ionization and fragmentation processes, excitation wavelengths and pulse durations at a fixed laser intensity have been found to drastically change ionization patterns. Intact molecular ions are produced when the wavelengths are non-resonant with the electronic levels of cations, whereas fragmentation proceeds to a large extent when the wave length is resonant with the electronic transitions. An ultimately short pulse presumably leads to the formation of fragment-free ions. Time-of-flight spectra of femtosecond pulse ionization of cyclohexadiene isomers, 2,3-dimethyl-1,3-butadiene, naphthalene, anthracene, and dioxin are presented. The great advantage of femtosecond laser mass spectrometry (FLMS) for the intact molecular ion formation is shown by referring briefly to the results obtained for dioxin. Some details of the experimental methods, such as a method of estimating irradiation intensity, are described. © 2007 Springer-Verlag.

DOI： 10.1007/978-3-540-38156-3-2

Publishing type：Research paper (scientific journal)  

4-Aminobenzonitrile derivatives have two excited states of similar energy: besides the benzene-like Lb state (also termed "locally excited" or LE state) one with charge-transfer (CT) character that is slightly higher in the isolated molecules. The CT state can be lowered by solvents of suitable polarity, so that dual fluorescence can be observed in them. It is controversial along which coordinate this state is displaced, although the amino-group twist is a wide-spread assumption. We investigated a number of such compounds by transient ionization in the gas phase, initially exciting the higher-lying La state (S2). Here we briefly review the previous results on 4-(dimethylamino)benzonitrile (the prototype of this class of molecules), 4-piperidino-, pyrrolidino- and pyrrolyl-benzonitrile and compare them with new results on 4-aminobenzonitrile and on the bridged derivative N-methyl-6-cyano-1,2,3,4-tetrahydroquinoline (NMC6). Although in the latter two molecules the CT state has never been detected before, we find the same relaxation path for all compounds: From S2, the wave packet passes through a conical intersection (CI); from there part of it reaches the S1 (Lb) state directly, whereas another part temporarily populates the CT state (also in NMC6), from where it goes around the CI also to the Lb well. The wave packet directly reaching the Lb well oscillates there along coordinates involving amino-group twist and wagging or molecular arching and a quinoidal distortion. These coordinates must be components of the CI displacement vector. A vibration involving bond-length alternation of the benzene ring is ascribed to a momentum caused by the electronic symmetry change in the CI, i.e., to the nonadiabatic coupling vector. Also the CT state involves amino-group twist, as to conclude from the anisotropy of the corresponding signal. The six-membered aliphatic ring in NMC6 hinders the twist and raises the CT state to an energy that is, however, still below the La state, so that it can be temporarily populated in a barrierless process. Also in aminobenzonitrile the CT state is between L a and Lb and is reached from La without a barrier. The twist is rationalized by vibronic interaction with a higher state that is π-antibonding between the amino group and the aromatic ring. This journal is © the Owner Societies.

DOI： 10.1039/b611877a

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cplett.2006.06.065

Publishing type：Research paper (scientific journal)  

Cyclohexane and 2,3-dimethyl-1,3-butadiene (DMBD) were ionized and fragmented by 0.8 μm femtosecond pulses with a typical intensity of 4 × 1013 W cm-2, which were resonant with the cation absorption of cyclohexane and DMBD. Their intact molecular ions were dominant at a pulse duration of 15 fs, whereas the molecules were heavily fragmented by excitation at 205-210 fs. Possible reasons for the formation of intact molecular ions by a short pulse are discussed in terms of the vibrational periods of excited precursor states. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2006.06.065

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp0619989

Publishing type：Research paper (scientific journal)  

We examined the femtosecond nonresonant ionization of organic amines with vertical ionization potentials as low as 5.95 eV. The quantitative evaluation of suppressed ionization relative to the single active electron approximation model was done by comparing the saturation intensity, Isat, in experiments and theory. ADK theory was found to be useful in predicting the ionization yield in the Isat scale within a factor of 2, even for molecules with very low ionization potentials. The degree of suppression was, however, smaller than that of benzene. The localization of electrons on the nitrogen atom was found to affect the ionization behavior under the strong laser field. The delocalized π electrons in benzene could not follow the laser field adiabatically, while those in localized molecular orbitals could. In addition, the growth of a tunneling barrier due to the screening effect in amines may be relatively smaller than that in benzene. © 2006 American Chemical Society.

DOI： 10.1021/jp0619989

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.1142/9789812707154_0003

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp053868q

Publishing type：Research paper (scientific journal)  

Naphthalene was ionized with 130 fs pulses of different polarizations at 1.4 μm. In contrast to the results of ionization by 0.8 μm pulses, fragmentation was dramatically suppressed and naphthalene molecular ions of up to 3+ were produced. The use of this simple model of ionization and large electron kinetic energy enabled us to study the electron-recollision-induced fragmentation and/or double ionization more precisely. The failure of the theoretical prediction of ion yield for the case of naphthalene prevented us from judging the electron recollision solely by a comparison with theoretical curves. Therefore, the effects of laser polarization on the ratios between differently charged states and between molecular and total ions were compared at the same effective (peak) intensity instead of average intensity. Comparison under the same effective intensity enabled us to identify the effects of ellipticity clearly. Evidence of the electron recollision was found in the doubly charged molecular ion formation but not in the fragmentation. The single-electron recollision event was not sufficient to induce fragmentation because of its low energy transfer efficiency. We concluded that the fragmentation originated in the unstable nature of the highly charged molecular ion itself and in the Coulomb explosion in the case of naphthalene. © 2005 American Chemical Society.

DOI： 10.1021/jp053868q

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp0516947

Publishing type：Research paper (scientific journal)  

The ring-cleavage reactions of a series of benzocycloalkenes were studied using an ArF excimer laser. Product formation was significantly suppressed in the presence of nitrogen; therefore, the presence of vibrationally excited states (hot molecules), as intermediates, was indicated. The product of highly strained benzocyclobutene was linearly proportional to the laser fluence, whereas those of benzocyclopentene and benzocyclohexene were proportional to the square of the laser fluence in the presence of nitrogen. These phenomena cannot be understood as photochemical bond cleavage in the electronic excited state, but instead appear to be the result of single- and two-photon reactions of hot molecules. The dissociation rate constants were evaluated by a statistical rate theory under the assumption that the reaction occurred from the hot molecule. The reaction rate of highly strained benzocyclobutene was predicted to be faster than the collisional rate with foreign gas, even if it had vibrational energy equivalent to one photon; however, the reaction rates of less strained benzocyclohexene were expected to compete with the collisional rate when the vibrational energy was equivalent to two photons. Benzocyclopentene was an intermediate case and showed both single- and two-photon reactions. The dissociation rate constant of 1.4 × 106 s-1 was successfully obtained from benzocyclopentene under collision-free conditions. This value was in fair agreement with the calculated value. The different dissociation rate constants of the molecules were well-explained in terms of the strain energy. Although the strain energy varies in a wide range (10-130 kJ mol-1), the simple model of the calculations reproduced the observed values of the CH2-CH2 bond dissociation in strained benzocycloalkenes. © 2005 American Chemical Society.

DOI： 10.1021/jp0516947

Publishing type：Research paper (scientific journal)  

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jphotochem.2004.10.008

Publishing type：Research paper (scientific journal)  

The two-photon chemistry of gaseous benzene was studied by laser flash photolysis using an ArF laser (193 nm) pumping to the S2 state. The major product was assigned to 1,3-hexadiene-5-yne, and one of the minor products was the phenyl radical. The formation mechanism is suggested to be as follows: hot benzene (S0** is formed by internal conversion from the S2 state, and hot benzene with two-photon energy (S0***) is formed from an excited state of S0**. S0*** is produced by a two-photon process, and its internal energy reaches 1243 kJ/mol. 1,3-Hexadiene-5-yne can form at rates much faster than the collision frequency (∼1010 s-1) under benzene 0.53 kPa in the presence of 51 kPa of propane. Collisional cooling is expected to quench the slow processes from S0** as well as the decomposition of 1,3-hexadiene-5-yne. 1,3-Hexadiene-5-yne and the phenyl radical can be the primary products of the two-photon fragments, which have been found by a multimass ion imaging technique. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2004.10.008

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

Coulomb explosion of hexa-fluorobenzene in an intense laser field (1.0 × 1016 W cm-2) was investigated using time-of-flight (TOF) mass spectrometry. The fluorine ions were mainly ejected parallel to the laser polarization, whereas the carbon ions were broadly distributed. The angular distribution features were totally different from those of benzene. Molecular dynamics simulations indicated that the substitution of fluorine atoms and/or ions caused ultrafast deformation of the carbon framework during the explosion. The effect of molecular alignment induced by the intense laser field is discussed. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2005.01.119

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cplett.2005.01.119

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cplett.2005.01.008

Publishing type：Research paper (scientific journal)  

Anthracene molecule was ionized with 130-fs pulses at two wavelengths, 0.8 and 1.4 μm. Anthracene ionized at 1.4 μm showed predominance of molecular ions with only few fragment ions, whereas excitation with 0.8-μm pulse produced many fragment ions. These observations are explained in terms of non-resonant (1.4 μm) vs. resonant (0.8 μm) excitations with the electronic levels of anthracene cation. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2005.01.008

Publishing type：Research paper (scientific journal)  

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

For the first time, femtosecond laser mass spectrometry (FLMS) has successfully detected 1,3,6-trichlorodibenzo-p-dioxin and 2,2′,5- trichlorobiphenyl. Non-chlorinated dibenzo-p-dioxin and biphenyl were also compared with the results of trichlorinated dioxins. The formation of parent ions without heavy fragmentation is an important goal for laser mass spectrometry; in other words, a high signal intensity ratio value of the parent ions/total ions (P/T ratios) is essential. The ratios were found to depend on the laser intensities as well as the wavelengths in FLMS. Generally, dioxins were more highly fragmented with increases in the laser intensity for all compounds studied here; the P/T ratios of non-chlorinated dioxins were higher with increases in the laser wavelength. The wavelength dependency for the chlorinated compounds was not distinct, probably because C-Cl bonds are easily dissociated in high-intensity laser fields, which induce further fragmentation. As a consequence of dissociation, the P/T ratios of the chlorinated dioxins were lower than the non-chlorinated dioxins. Within our experimental parameters, the optimum laser conditions were 1500 nm excitation with an intensity of 3.0 × 1013 W/cm2 for 1,3,6-trichlorodibenzo-p-dioxin and 2000 nm and 3.3 × 1013 W/cm2 for 2,2′,5-trichlorobiphenyl. © 2005 The Japan Society for Analytical Chemistry.

DOI： 10.2116/bunsekikagaku.54.127

CiNii Article

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.2184/lsj.33.12

CiNii Article

Publishing type：Research paper (scientific journal)  

For the first time, femtosecond laser mass spectrometry (FLMS) has successfully detected 1, 3, 6-trichlorodibenzo-p-dioxin and 2, 2′, 5-trichlorobiphenyl. Non-chlorinated dibenzo-p-dioxin and biphenyl were also compared with the results of trichlorinated dioxins. The formation of parent ions without heavy fragmentation is an important goal for laser mass spectrometry ; in other words, a high signal intensity ratio value of the parent ions/total ions (P/T ratios) is essential. The ratios were found to depend on the laser intensities as well as the wavelengths in FLMS. Generally, dioxins were more highly fragmented with increases in the laser intensity for all compounds studied here ; the P/T ratios of non-chlorinated dioxins were higher with increases in the laser wavelength. The wavelength dependency for the chlorinated compounds was not distinct, probably because C-Cl bonds are easily dissociated in high-intensity laser fields, which induce further fragmentation. As a consequence of dissociation, the P/T ratios of the chlorinated dioxins were lower than the non-chlorinated dioxins. Within our experimental parameters, the optimum laser conditions were 1500 nm excitation with an intensity of 3.0×10^<13> W/cm^2 for 1, 3, 6-trichlorodibenzo-p-dioxin and 2000 nm and 3.3×10^<13> W/cm^2 for 2, 2′, 5-trichlorobiphenyl.

DOI： 10.2116/bunsekikagaku.54.127

CiNii Article

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.2184/lsj.33.12

CiNii Article

The ionization and fragmentation of 2,3-dimethyl-1,3-butadiene of a femtosecond laser have been studied at various pulse durations, which were changed from 35 fs to 1 ps. A reflectron-type time of flight mass spectrometer (TOF-MS) was used for ion detection. Molecules were ionized under a strong laser field and formed parent ions. Some were fragmented, resulting in a drastic increase of ionic species. Fragmentation was dominant when a long duration pulse was used, probably because the parent and large fragmented ions were further decomposed into small fragmented ions. Such heavy fragmentation may cause an underestimation of I_sat.

DOI： 10.2184/lsj.32.717

CiNii Article

Other URL： https://jlc.jst.go.jp/DN/JALC/00244141255?from=CiNii

© 2004 Elsevier B.V. All rights reserved. Pumping a molecule by a femtosecond, pulse to an electronically excited state S2 creates a vibrational wave packet in this state. Ultrafast internal conversion through a conical intersection may give rise to a periodic motion in a lower potential well, which can be observed as a coherent oscillation in pump-probe spectroscopy. If the slope on entering the well excites the vibration, its assignment gives information on the relaxation or reaction path direction. In the experiment in this chapter the molecules are excited to the S2 (La, symmetry 2A) state by a 70 fs pulse at 270 nm. The La and CT states are just two locations on one potential energy surface (PES), and the Lb PES in the form of a conical intersection (CI) crosses this surface. The wave packet passes through the CI and branches there. The one entering first into the S1 well oscillates there coherently, whereas the other arriving later from the CT state seems to have lost its coherence. The vibration is assigned in PIPBN to amino-group wagging (planarization/pyramidalization) in S1.

DOI： 10.1016/B978-044451656-5/50061-X

Publishing type：Part of collection (book)  

© 2004 Elsevier B.V. All rights reserved. Pumping a molecule by a femtosecond, pulse to an electronically excited state S2 creates a vibrational wave packet in this state. Ultrafast internal conversion through a conical intersection may give rise to a periodic motion in a lower potential well, which can be observed as a coherent oscillation in pump-probe spectroscopy. If the slope on entering the well excites the vibration, its assignment gives information on the relaxation or reaction path direction. In the experiment in this chapter the molecules are excited to the S2 (La, symmetry 2A) state by a 70 fs pulse at 270 nm. The La and CT states are just two locations on one potential energy surface (PES), and the Lb PES in the form of a conical intersection (CI) crosses this surface. The wave packet passes through the CI and branches there. The one entering first into the S1 well oscillates there coherently, whereas the other arriving later from the CT state seems to have lost its coherence. The vibration is assigned in PIPBN to amino-group wagging (planarization/pyramidalization) in S1.

DOI： 10.1016/B978-044451656-5/50061-X

Publishing type：Research paper (scientific journal)  

A series of alkylarenes (AR) was excited by an ArF excimer laser in the gas phase. The neutral radical was observed by transient absorption spectroscopy without traces of emission, triplet state, or cation radical. Single and multiphoton (up to three-photon) processes were observed even though molecules have similar structures. This presents a quite different feature from ordinary photochemistry in the condensed phase. Neutral radical production was explained well by the hot molecule mechanism and compared with statistical reaction theory. The differences between multiphoton reactions in the condensed phase and those in the gas phase were discussed. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/S1010-6030(03)00389-7

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

The La-like S2 state of 4-(1-piperidino) -benzonitrile and the corresponding 3,5-dimethyl-piperidino derivative was excited at 270 nm in the gas phase at 130°C. Nonresonant multiphoton ionization at infrared wavelengths (810 and 1300 nm) with mass-selective detection of the ion yields then probed the subsequent processes. Two groups of time constants were found: in the range <2 ps and in the 100 ps range. In addition, a coherent oscillation with period 1.06 and 1.18 ps for the unsubstituted and substituted species were monitored until about 10 ps. The sub-picosecond time constants can be assigned to relaxation from S2 through a conical intersection to both S1 (Lb-like) and a charge transfer (CT) state. These two states then equilibrate within about 1.9 ps. The oscillation must be a vibration in Lb, because this is the only state still populated at 10 ps. It is suggested to assign it to the amino-group wagging (planarization/pyramidalization). It indicates a component of the direction into which the conical intersection is displaced from the Lb minimum. The ultrafast relaxation times suggest, however, that additional coordinates are involved in the process, probably amino-group twist and bond stretching in the benzene ring. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemphys.2003.09.011

DOI： 10.2184/lsj.32.717

J-GLOBAL

DOI： 10.1039/b313691d

Other URL： http://orcid.org/0000-0002-6810-7774

DOI： 10.1016/j.chemphys.2003.09.011

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S1010-6030(03)00389-7

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (international conference proceedings)  

4-(N-pyrrolidinyl)benzonitrile and 4-(N-pyrrolyl)benzonitrile were excited by an ultrashort pulse at 270 nm to their La (S2) states and then probed by ionization at long wavelengths. Parent and fragment ion signals show components with time constants < 100 fs which we attribute to ultrafast relaxation to the Lb (S1) state. From this short time we infer a conical intersection between the Lb and L a surfaces. The wave packet can branch there, one part going temporarily to a strongly displaced state. Its shift was concluded from an anisotropy observed only there. The only excited state known to have a large displacement is the charge-transfer (CT) state. The positive anisotropy indicates that the CT state belongs to the 2A species for both molecules. For pyrrolylbenzonitrile, this is in contrast to previous assignments. The anisotropy, and a coherent oscillation observed in pyrrolidinylbenzonitrile, support the idea that the amino-group twist is an important component of the CT reaction coordinate.

DOI： 10.1039/b313691d

Publishing type：Research paper (scientific journal)  

4-(N-pyrrolidinyl) benzonitrile and 4-(N-pyrrolyl) benzonitrile were excited by an ultrashort pulse at 270 nm to their L-a (S-2) states and then probed by ionization at long wavelengths. Parent and fragment ion signals show components with time constants &lt; 100 fs which we attribute to ultrafast relaxation to the L-b (S-1) state. From this short time we infer a conical intersection between the Lb and La surfaces. The wave packet can branch there, one part going temporarily to a strongly displaced state. Its shift was concluded from an anisotropy observed only there. The only excited state known to have a large displacement is the charge-transfer (CT) state. The positive anisotropy indicates that the CT state belongs to the 2A species for both molecules. For pyrrolylbenzonitrile, this is in contrast to previous assignments. The anisotropy, and a coherent oscillation observed in pyrrolidinylbenzonitrile, support the idea that the amino-group twist is an important component of the CT reaction coordinate.

DOI： 10.1039/b313691d

Publishing type：Research paper (scientific journal)  

We detected parent and fragment ions from 14 chlorinated and a few fluorinated compounds as well as dibenzo-p-dioxin (dioxin) in intense laser fields. The irradiation pulse had an intensity from 1 × 1013 to 1 × 1015 W cm-2, with a 130-fs pulse duration at a central wavelength of 800 nm. Irradiation at this intensity led to a singly ionized species and a small amount of atomic ions, indicating the onset of Coulomb explosions. We have previously reported finding a key factor in determining the parent and/or fragment ion formations of organic hydrocarbons with an intense femtosecond laser pulse [Harada, H.; et al. Chem. Phys. Lett. 2001, 342, 563-570]. This key factor is a requirement for parent ion predominance if the excitation laser wavelength and the absorption spectra of the target cation are in nonresonance, and vice versa. Use of this factor has been found to be effective for molecules other than hexachlorobutadiene. The threshold intensities Isat at the infinity ionization rate were determined and are reasonably comparable to those of previously reported hydrocarbons.

DOI： 10.1021/jp022626c

Publishing type：Research paper (scientific journal)  

EuO (Europium(II) oxide) nanocrystals are prepared under irradiation by means of an ArF excimer laser. The formation of EuO nanocrystals with the clear lattice fringes was confirmed by TEM image. The crystal growth was monitored by the emission spectra.

DOI： 10.1246/cl.2003.708

Publishing type：Research paper (scientific journal)  

4-Dimethylamino-benzonitrile was excited in the gas phase at 270 nm into the S2 (La) state and probed by femtosecond time-resolved photoionization at 2 μm. Coherent oscillations were detected in the transient ion signal. We claim that from S2, the molecule relaxes through a conical intersection and, going backwards along the charge-transfer (CT) reaction coordinate, enters into the S1 (Lb) well, where it vibrates along the amino-group twist and inversion. Probably mainly the last slope stimulates these oscillations. We conclude that the conical intersection - and hence also the CT state - is displaced from the L b minimum in a direction containing the twist and inversion as components and that inversion is part of the nonadiabatic coupling vector. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0009-2614(03)00979-5

DOI： 10.1021/jp022626c

Other URL： http://orcid.org/0000-0002-6810-7774

Other URL： http://orcid.org/0000-0002-6810-7774

DOI： 10.1016/S0009-2614(03)00979-5

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

The deactivation process of excited 1-(dimethylamino)-9-fluorenone (1-DMAF) was investigated by means of steady-state and time-resolved fluorescence spectroscopy. Fluorescence decay profiles for 1-DMAF, which has a relatively short lifetime (several tens of picoseconds in low viscosity solvents at ambient temperature) are much affected by the fluidity of the surrounding solvent. The lifetimes increase in glassy solvents at 77 K as well as with increasing viscosity. These results indicate that conformational relaxation by the dimethylamino group plays an important role in the deactivation process of 1-DMAF. Detailed analysis of the temperature dependence of the fluorescence lifetime revealed that the conformational relaxation process has a very small intramolecular activation barrier (5.4 kJ/mol). Results of MO calculations suggest that the dimethylamino moiety of 1-DMAF is pretwisted in the ground state and that the most stable structure in the excited state is a twisted intramolecular charge transfer (TICT) state. 1-DMAF could be a new model molecule that exhibits the TICT phenomena.

DOI： 10.1021/jp0203604

Publishing type：Research paper (scientific journal)  

The kinetic-energy distributions of multiply charged carbon ions produced by the Coulomb explosion of benzene are reported to be highly anisotropic in the direction of the laser electric field. Specifically, the Coulomb explosion of benzene at laser intensity of 8.0 × 1016 W cm-2 and the C4+ ion and proton with large kinetic energy and at a higher angle are observed. The molecular dynamics (MD) simulations reveal that the explosion process is anisotropic for the laser electric field.

DOI： 10.1063/1.1492275

Publishing type：Research paper (scientific journal)  

Cyclophane derivatives were irradiated with an ArF excimer laser in the gas phase. No triplet states, fluorescence, or cation radicals were observed in the transient spectra. The CH2-CH2 bonds dissociated, forming corresponding xylylenes by a two-photon process. The bond dissociations were explained in terms of a multiphoton reaction of hot molecules formed by an internal conversion. In addition, a slow rise of xylylene that originated in the single photon dissociation process of hot cyclophane was observed in the case of methyl-substituted paracyclophanes under low pressure conditions. The specific reaction rates of the dissociations of highly strained paracyclophanes were well explained by a statistical reaction theory, if a simple consideration of strain energy was made in the calculations.

DOI： 10.1021/jp0120817

DOI： 10.1063/1.1492275

Other URL： http://orcid.org/0000-0002-6810-7774

DOI： 10.1021/jp0120817

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp0203604

Other URL： http://orcid.org/0000-0002-6810-7774

Publishing type：Research paper (scientific journal)  

Energy-gap dependency for radiationless deactivation from excited states of various molecules having strong intramolecular charge transfer (ICT) character has been investigated by observing fluorescence quenching on addition of alcohols. Molecules having strong ICT excited states were classified into three groups: (a) molecules that underwent considerable fluorescence quenching by ethanol (quenching constant, K SV > 20 M -1) and for which radiationless deactivation in protic solvents was much faster than anticipated from the ordinary energy-gap law observed in aprotic solvents, (b) molecules whose fluorescence exhibited substantial red shifts, and (c) molecules whose fluorescence were barely affected by the addition of ethanol (K SV < 1 M -1) and for which the energy-gap dependences on radiationless deactivation in protic solvents were not so different from those in aprotic solvents. Typical fluorophores for each case, i.e., a, b, and c, were aminoanthraquinone, aminophthalimide, and aminocoumarin, respectively. Differences in the fluorescence quenching phenomena are discussed in terms of the molecular structure and the hard-soft anionic character of the excited states, governed by changes in charge density on the carbonyl oxygen. An excited molecule having a hard anionic character on a specific site within the molecule, classified as group a, was concluded to undergo considerable fluorescence quenching through an intermolecular hydrogen bonding interaction with an alcohol having a hard cationic character. On the other hand, fluorescence of an excited molecule having a soft anionic character, classified as group c, cannot be quenched well by an alcohol because of the weak interaction on the carbonyl oxygen. The anomalous behavior of the excited aminophthalimides (group b), which are classified as hard anions but do not undergo fluorescence quenching, suggested the possibility that molecular rigidity is another factor controlling the radiationless deactivation process induced by hydrogen bonding.

DOI： 10.1021/jp0117213

CiNii Article

DOI： 10.1021/ja015803g

PubMed

CiNii Article

Publishing type：Research paper (scientific journal)  

Two pairs of organic molecules (2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene; 1,4-cyclohexadiene, 1,3-cyclohexadiene) were irradiated with a high-intensity 120-fs laser pulse in the intensity region of 1014 W cm-2. One molecule in each pair had no allowed electronic transition in the cation at the excitation wavelength of 800 nm, resulting in parent ion dominance. In contrast, the counter molecule, which had a similar structure but with absorption in the cation at the excitation wavelength, showed heavy fragmentation with a negligibly small signal of the parent ion. The previously reported observations are explainable on the basis of the proposed mechanism for fragmentation in femtosecond ionization. © 2001 Elsevier Science B.V.

DOI： 10.1016/S0009-2614(01)00662-5

CiNii Article

Publishing type：Research paper (scientific journal)  

The hot molecule (S0**) is in a highly vibrationally excited state formed by rapid internal conversion from initially prepared electronic excited states. The importance and predominance of the S0** mechanism in VUV gas phase photochemistry has been demonstrated. In this account, the fundamental physicochemical properties of S0** are discussed in order to understand the characteristic features of S0** reactions, and VUV laser chemistry is reviewed from the following two points of view: 1) The generalization and classification of VUV chemistry for a variety of molecules, including the hot molecule mechanism and other competitive mechanisms; 2) A new strategy of multiphoton chemistry that employs hot molecule as an intermediate. Internal conversion is a dominant deactivation process for many molecules in the VUV region. Aromatic hydrocarbons and olefins are the representative examples of S0** reactions. However, fluorescence and intersystem crossing are major deactivation processes in some cases such as large condensed aromatic hydrocarbons. The reactions of chlorinated compounds and phenols are explained by other reaction mechanisms such as direct dissociation and predissociation. Carbonyl compounds and some amines are classified into the intermediate cases. Due to the large molar extinction coefficient and relatively long lifetime of S0**, the multiphoton absorption process can be induced by a single nanosecond laser pulse. As a result of fast internal conversion and intramolecular energy redistribution, the second photon and further photons will not be absorbed by the molecule in the electronic excited state but by that in the S0**, and the photon energy of the multiphoton is accumulated as vibrational energy. Therefore, ionization is minor process in the case of the multiphoton reaction of S0**. The neutral radical formation is predominant in the dissociation reaction, and the rate constant increases because the internal energy is multiplied by the multiphoton absorption process. The applications of these findings lie in the following: 1) Large molecules of which the single-photon hot molecule reaction rate is small; 2) Molecules which have been deemed to be photoinert.

DOI： 10.1246/bcsj.74.579

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

DOI： 10.1016/S1010-6030(01)00486-5

CiNii Article

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

DOI： 10.1016/S0009-2614(01)00662-5

CiNii Article

Kind of work：Single Work  

DOI： 10.1021/ja015803g

PubMed

CiNii Article

Kind of work：Single Work  

DOI： 10.1246/bcsj.74.579

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

DOI： 10.1021/jp0117213

CiNii Article

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

DOI： 10.1021/jp004560w

CiNii Article

Publishing type：Research paper (international conference proceedings)  

Analysis of coulomb explosion of benzene in high intensity laser fields was presented. The irradiation intensity from an Ti:sapphire femtosecond laser with a pulse width of 120 fs was obtained. Detection of Cq+ and H+ was obtained in the time-of-flight spectra accompanied by multiple peaks. The explosion for the Coulomb explosion of C60 was successfully reproduced as classical simulations of molecular dynamics.

Publishing type：Research paper (international conference proceedings)  

Photoionization of polychlorinated compounds with an intense femtosecond laser pulse was demonstrated. Ti:sapphire laser system was used and the ion species were recorded using a reflectron time-of-flight mass spectrometer. The spectrometer was placed parallel to the electric field of the linearly polarized laser beam. Ions of polychlorinated compounds were detected in a laser intensity region less than 1×1014W cm-2 and the mechanism was explained in terms of non-resonant multiphoton ionization.

Publishing type：Research paper (scientific journal)  

Solvent and substituent effects on the competition between internal conversion and triplet formation were studied systematically for aminofluorenones and their N-methylated derivatives. Intersystem crossing (ISC) was found to be the dominant process for the singlet excited 1-amino- and 1-methylaminofluorenone in all solvents. The short fluorescence decay time of these compounds does not originate from intramolecular hydrogen bonding induced internal conversion but it is due to the fast triplet formation. Rather slow (kISC ≤ 4.8 × 107 s-1) and solvent insensitive intersystem crossing characterizes the photophysical behavior of 2-, 3- and 4-aminofluorenones but their internal conversion rate strongly increases with solvent polarity. The change of the internal conversion rate constants with molecular structure and solvent can be rationalized in terms of the energy gap law.

DOI： 10.1039/b009860o

CiNii Article

New research fields have opened up that are related to the interactions between molecules and high-intensity optical fields where the laser intensity ranges from 1012-1017 W cm-2. A broad outline of this area will be described from the perspective of products and new techniques for beam generation. Studies of large molecules have begun and some examples are introduced herein. Parent ions with little fragmentation are found to form in the intensity region below 1016 W cm-2. The formation of intact ions can be used in femtosecond laser mass spectrometry. In the intensity region above 1016 Wcm-2, electrons are stripped from the molecules by optical field ionization and the highly charged ions can undergo a Coulomb explosion. Coulomb explosions of benzene and C60 have been demonstrated, and the mechanism can be analyzed by means of molecular dynamics simulations. A high intensity femtosecond laser beam can be converted to radiation sources of coherent VUV light, X-rays etc. and some possibilities for new chemical applications will be discussed. © 2000 Japanese Photochemistry Association. All rights reserved.

DOI： 10.1016/S1389-5567(00)00009-5

Publishing type：Research paper (scientific journal)  

A VUV (vacuum-UV) three-photon hot molecule reaction is demonstrated in this study for gaseous triphenylmethane (TPM). A TPM radical was derived from vibrationally hot TPM, which sequentially absorbed the second and third photons within a laser pulse. In the condensed phase, TPM radical was formed by the deprotonation of a cation radical, which was formed by the two-photon ionization. The multiphoton reaction via a hot molecule is a special case which can produce a neutral radical directly. This study also shows that more than two high-energy photons (VUV) can be absorbed and accumulated as vibrational energy. It should be emphasized that an internal conversion is not a useless photophysical process, but a very interesting process for forming an important intermediate in multiphoton laser chemistry. © 2000 American Chemical Society.

DOI： 10.1021/jp003017c

CiNii Article

Steady-state and time-resolved fluorescence behavior of 4-cyano-4′-pentylbiphenyl (5CB) in polymer-dispersed liquid crystal (PDLC) films sandwiched between two quartz substrates was characterized by the surfacelimited excitation (SLE) and through-film excitation (TFE) methods, which were used to discriminate the emissions from the interface layer with the substrate and from the interior domain. Although PDLC films showed both the monomer and excimer emissions of 5CB, SLE gave a substantially greater contribution of the former in the fluorescence than TFE. By contrast, a neat nematic film of 5CB showed exclusively the excimer emission independently of the excitation methods. Time-resolved analysis of the excimer emission from PDLC films revealed double-exponential decay profiles with shorter-lived (1.5-1.8 ns) and longer-lived (12-17 ns) components, in which the former is dominant for the excimer emission obtained by SLE, while the latter takes a major part for that obtained by TFE. By contrast, the excimer emission from a neat nematic film of 5CB showed a single-exponential decay with a ∼7 ns lifetime independently of the excitation methods. The unique fluorescence behavior of the PDLC films has been discussed in terms of different molecular aggregation features of 5CB in the interface layer and in the interior domain. © 2000 American Chemical Society.

Publishing type：Research paper (scientific journal)  

Steady-state and time-resolved fluorescence behavior of 4-cyano-4′-pentylbiphenyl (5CB) in polymer-dispersed liquid crystal (PDLC) films sandwiched between two quartz substrates was characterized by the surfacelimited excitation (SLE) and through-film excitation (TFE) methods, which were used to discriminate the emissions from the interface layer with the substrate and from the interior domain. Although PDLC films showed both the monomer and excimer emissions of 5CB, SLE gave a substantially greater contribution of the former in the fluorescence than TFE. By contrast, a neat nematic film of 5CB showed exclusively the excimer emission independently of the excitation methods. Time-resolved analysis of the excimer emission from PDLC films revealed double-exponential decay profiles with shorter-lived (1.5-1.8 ns) and longer-lived (12-17 ns) components, in which the former is dominant for the excimer emission obtained by SLE, while the latter takes a major part for that obtained by TFE. By contrast, the excimer emission from a neat nematic film of 5CB showed a single-exponential decay with a ∼7 ns lifetime independently of the excitation methods. The unique fluorescence behavior of the PDLC films has been discussed in terms of different molecular aggregation features of 5CB in the interface layer and in the interior domain. © 2000 American Chemical Society.

Publishing type：Research paper (scientific journal)  

The photodecarbonylation of gaseous coumarin was studied using an ArF excimer laser. The triplet state, fluorescence, and cation radical of coumarin were not observed in the transient spectra. The addition of nitrogen effectively quenched the formation of 2,3-benzofuran, indicating that 2,3-benzofuran was derived from the highly vibrationally excited state of coumarin. Transient absorption was proportional to the square of the laser fluence. All of the results showed that the hot coumarin was an intermediate in the two-photon decarbonylation reaction. The decarbonylation reaction of coumarin is the first example of the multiphoton reaction of hot molecules other than hydrocarbons. This new photochemical reaction pathway of coumarin was opened by the hot molecular mechanism. © 2000 American Chemical Society.

DOI： 10.1021/jp993339k

CiNii Article

Publishing type：Research paper (scientific journal)  

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

DOI： 10.1021/jp992469q

CiNii Article

Kind of work：Single Work  

DOI： 10.1021/jp993702n

CiNii Article

Kind of work：Single Work  

DOI： 10.1021/jp993339k

CiNii Article

Kind of work：Single Work  

DOI： 10.1021/jp003017c

CiNii Article

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Kind of work：Single Work  

DOI： 10.1016/S1389-5567(00)00009-5

Kind of work：Single Work  

DOI： 10.1039/b009860o

CiNii Article

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

Photophysical properties of fluorenone and 12 aminofluorenone derivatives were investigated systematically by fluorescence quantum yield and picosecond lifetime measurements in cyclohexane, benzene, acetonitrile, and ethanol. Aminofluorenones underwent efficient deactivation in ethanol, except for the 1-aminofluorenone derivatives. An appreciable deuterium isotope effect on the radiationless deactivation (knr) was observed in all aminofluorenones. The largest effect was observed for 4-aminofluorenone (knr(EtOH)/knr(EtOD) = 1.9), while the smallest was for 1-aminofluorenone (knr(EtOH)/knr(EtOD) = 1.2). The radiationless deactivation in ethanol was concluded to be induced through an intermolecular hydrogen bond between the hydroxyl hydrogen of ethanol and the carbonyl oxygen of aminofluorenones. The possibility of a twisted intramolecular charge-transfer state in the case of 1-(dimethylamino)fluorenone was explored by semiempirical molecular orbital calculation.

DOI： 10.1021/jp980158u

CiNii Article

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Other URL： http://orcid.org/0000-0002-6810-7774

Kind of work：Single Work  

DOI： 10.1021/jp980158u

CiNii Article

Kind of work：Single Work  

DOI： 10.1021/jp981975x

CiNii Article

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

The molecular mechanism of radiationless deactivation from the excited singlet state of aminoanthraquinones (AAQ) induced by alcohols and hydroperoxides was investigated by time-resolved picosecond fluorescence measurements. AAQ suffered substantial fluorescence quenching with red shifts of their λmax in benzene solution upon addition of alcohol and hydroperoxide. Primary alcohols exhibited the largest quenching effects among 26 alcohols examined, while tertiary alcohols were least effective. The Stern-Volmer constants were well correlated with the 13C NMR chemical shift of the carbinol carbon atom and the contact molecular surface area of the hydroxyl hydrogen of the quenchers, while it apparently did not depend upon pKa values. Contact molecular surface area was revealed to be a good quantitative parameter for the steric effect in the intermolecular hydrogen-bonding interaction. The steric factor was dominant in the fluorescence-quenching process, but the electronic factor becomes evident among the molecules having the same steric factor such as benzyl alcohol derivatives, where the Hammet plot showed a good linearity. Fluorescence decay kinetics clearly showed that two emitting levels were involved such as the fluorescent state in benzene and a fully relaxed state in which reorganization of the surrounding alcohol was established. Estimated lifetimes of the fully relaxed states were longer than those in neat alcohol by a factor of 30. The results were interpreted that there were at least two relaxation pathways by alcohol reorganization through the intermolecular hydrogen bond. A specific reorganization of alcohol to AAQ induced relaxation from the fluorescent state in benzene to a relaxed, emissive state and to another relaxed, nonfluorescent state. The latter leads to an efficient radiationless deactivation. The relaxed emissive state corresponds to the excited state of intermolecular hydrogen-bonded species of AAQ with the alcohol in the ground state in which the hydroxyl group of alcohol interacts through an in-plane mode against the carbonyl oxygen of AAQ. Another relaxed nonfluorescent state is formed through an out-of-plane mode interaction between AAQ and the hydroxyl group of alcohol.

DOI： 10.1021/jp970581n

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Publishing type：Research paper (scientific journal)  

Kind of work：Single Work  

DOI： 10.1021/jp970581n

CiNii Article

Total pages：v.   Book type：Scholarly book

CiNii Books

Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Presentation type：Oral presentation (general)  

Presentation type：Poster presentation