Shinji Hasegawa

Electricity Generation from Decomposition of Hydrogen Peroxide

This paper demonstrates a direct H 2 O 2 fuel cell (DHPFC). The cell converts the energy released by H 2 O 2 decomposition with H + and OH - ions into electricity, and produces water and oxygen. In the experiment, we used amicrofluidic cell, in which acid and alkaline electrolytes contact with each other. The measured power density of the cell is comparable to that of a typical air-breathing direct-methanol fuel cell. The DHPFC emits no CO 2 , uses simply handled aqueous fuels, and requires no expensive membrane-electrolyte assemblies. These advantages may allow the DHPFC to be a promising candidate for practical fuel cells.

Structure of copper- and H2-phthalocyanine thin films on MoS2 studied by angle-resolved ultraviolet photoelectron spectroscopy and low energy electron diffraction

Angle-resolved ultraviolet photoelectron spectra (ARUPS) of copper phthalocyanine (CuPc) and metal-free phthalocyanine (H2Pc) films (thickness from monolayer to 50–80 A) on cleaved MoS2 substrates were measured using monochromatic synchrotron radiation. Observed take-off angle (θ) and azimuthal angle (φ) dependencies of the top π band intensity were analyzed quantitatively by the single-scattering approximation theory combined with molecular orbital calculations. The analysis indicated that the molecules lie flat on the MoS2 surface in monolayer films of CuPc and H2Pc. The azimuthal orientation of the molecules (angle between molecular axis and surface crystal axis of MoS2), was found to be about −7°, −37°, or −67° for both monolayer films of CuPc and H2Pc. In the azimuthal orientation, the analyses indicated that there are only molecules with conterclockwise rotation, although both clockwise and counterclockwise rotations are expected. From the low energy electron diffraction, the two-dimensional lattice...

Intermolecular energy-band dispersion in oriented thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) by angle-resolved photoemission

Angle‐resolved ultraviolet photoemission spectra using synchrotron radiation were measured for oriented thin films of bis(1,2,5‐thiadiazolo)‐p‐quinobis(1,3‐dithiole) (BTQBT) on graphite. From the photon energy dependence of normal emission spectra, the energy‐band dispersion of π‐bands were observed for the highest (HOMO) and next highest (NHOMO) bands. This is the first observation of intermolecular dispersion in a single‐component organic molecular crystal. The results demonstrate that the BTQBT molecules have a strong intermolecular interaction, which can be derived from the introduction of a covalent interaction between sulfur atoms in addition to the usual intermolecular interaction by van der Waals forces.

Ultraviolet photoelectron spectra of C84 and KxC84

Abstract Ultraviolet photoelectron spectra of C 84 , one of the fullerene family compounds, and of potassium-dosed C 84 have been measured with synchrotron radiation. The spectra of C 84 are compared with those of C 60 and C 70 . The photoemission spectral onset of C 84 is 1.3 eV below the Fermi level, which is smaller by 0.5 eV than that of C 60 or C 70 . This indicates its small band gap, which was expected from its absorption spectra. Upon potassium dosing, a new band becomes distinct between the Fermi level and the highest occupied molecular orbital band. The new band edge does not cross the Fermi level, which indicates that potassium-dosed C 84 is not metallic but a semiconductor.

Spectroscopic Investigation of Peridinin Analogues Having Different π-Electron Conjugated Chain Lengths: Exploring the Nature of the Intramolecular Charge Transfer State

The lifetime of the lowest excited singlet (S(1)) state of peridinin and many other carbonyl-containing carotenoids and polyenes has been reported to depend on the polarity of the solvent. This effect has been attributed to the presence of an intramolecular charge transfer (ICT) state in the manifold of excited states for these molecules. The nature of this ICT state has yet to be elucidated. In the present work, steady-state and ultrafast time-resolved optical spectroscopy have been performed on peridinin and three synthetic analogues, C(33)-peridinin, C(35)-peridinin, and C(39)-peridinin, which have different numbers of conjugated carbon-carbon double bonds. Otherwise, the molecules are structurally similar in that they possess the same functional groups. The trends in the positions of the steady-state and transient spectral profiles for this systematic series of molecules allow an assignment of the spectral features to transitions involving the S(0), S(1), S(2), and ICT states. A kinetics analysis reveals the lifetimes of the excited states and the dynamics of their excited state deactivation pathways. The most striking observation in the data is that the lifetime of the ICT state converges to the same value of 10.0 +/- 2.0 ps in the polar solvent, methanol, for all the peridinin analogues, regardless of the extent of pi-electron conjugation. This suggests that the ICT state is highly localized on the lactone ring, which is a common structural feature in all the molecules. The data further suggest that the S(1) and ICT states behave independently and that the ICT state is populated from both S(1) and S(2), the rate and efficiency from S(1) being dependent on the length of the pi-electron chain of the carotenoid and the solvent polarity.

Angle‐resolved photoemission spectroscopy of ultrathin films of H2‐phthalocyanine on MoS2 surfaces

The angle‐resolved ultraviolet photoelectron spectra were measured for ultrathin films of H2–phthalocyanine deposited on cleaved MoS2 surfaces using synchrotron radiation. The take‐off angle (θ) dependence of photoelectron intensity from the highest π band showed a sharp maximum at θ=34°. The observed angular distribution could be explained excellently by an angular distribution calculated for flat‐lie orientation of the molecules using independent‐atomic‐center approximation combined with molecular orbital calculation. The results confirm that the calculation method is useful to describe photoelectron angular distribution from thin films of large and complex organic molecules and H2‐phthalocyanine molecules lie flatly on MoS2 surface.

Ultraviolet photoelectron spectra of C76 and KxC76

Abstract Ultraviolet photoelectron spectra of C76, one of the fullerene family of compounds, have been measured with a synchroton radiation light source. The photoemission spectral onset is 1.3 eV below the Fermi level, which is equal to that of C84 but is about 0.5 eV smaller than that of C60 or C70. The relative intensity of the photoemission spectral features is independent of the incident photon energy change. Photoemission spectral changes for C76 during potassium dosing are also measured. A new band becomes distinct between the Fermi level and the HOMO band, when the potassium content (x in KxC76) is equal to or greater than 1.1. The spectral onset moves toward the Fermi level with increasing potassium dosage, approaching it but never crossing it. This indicates that potassium-dosed C76 could be a narrow gap semiconductor.

Effect of Molecular Symmetry on the Spectra and Dynamics of the Intramolecular Charge Transfer (ICT) State of Peridinin

The spectroscopic properties and dynamics of the excited states of two different synthetic analogues of peridinin were investigated as a function of solvent polarity using steady-state absorption, fluorescence, and ultrafast time-resolved optical spectroscopy. The analogues are denoted S-1- and S-2-peridinin and differ from naturally occurring peridinin in the location of the lactone ring and its associated carbonyl group, known to be obligatory for the observation of a solvent dependence of the lifetime of the S(1) state of carotenoids. Relative to peridinin, S-1- and S-2-peridinin have their lactone rings two and four carbons more toward the center of the π-electron system of conjugated carbon-carbon double bonds, respectively. The present experimental results show that as the polarity of the solvent increases, the steady-state spectra of the molecules broaden, and the lowest excited state lifetime of S-1-peridinin changes from ∼155 to ∼17 ps which is similar to the magnitude of the effect reported for peridinin. The solvent-induced change in the lowest excited state lifetime of S-2-peridinin is much smaller and changes only from ∼90 to ∼67 ps as the solvent polarity is increased. These results are interpreted in terms of an intramolecular charge transfer (ICT) state that is formed readily in peridinin and S-1-peridinin, but not in S-2-peridinin. Quantum mechanical computations reveal the critical factors required for the formation of the ICT state and the associated solvent-modulated effects on the spectra and dynamics of these molecules and other carbonyl-containing carotenoids and polyenes. The factors are the magnitude and orientation of the ground- and excited-state dipole moments which must be suitable to generate sufficient mixing of the lowest two excited singlet states.

Angle-resolved photoemission from oriented thin films of naphthacene: comparison with theoretical spectra

Abstract The comparison was made between the measured and calculated take-off angle dependencies of the valence-band photoelectron spectra for the thin films of naphthacene on HOPG graphite. A good agreement was obtained between them, and the molecular orientation in the thin films was estimated. In the present calculation, the single-scattering of the outgoing photoelectrons was taken into account. The calculation of the full valence-band spectra is the first example to the organic thin films.

PHOTODEGRADATION OF POLY(TETRAFLUOROETHYLENE) AND POLY(VINYLIDENE FLUORIDE) THIN FILMS BY INNER SHELL EXCITATION

Ion time-of-flight (TOF) mass spectra of poly(tetrafluoroethylene) (PTFE) and poly(vinylidene fluoride) (PVDF) thin films near fluorine and carbon K-edges were observed. For PTFE thin films, peaks corresponding to F+, CF+, and appeared, while for PVDF F+ and H+ were mainly observed. They indicate that for PTFE the polymer chain (C–C bonds) as well as C–F bonds are broken by irradiation of photons near fluorine and carbon K-edges, while for PVDF the bond scission occurs mainly at the C–F and C–H bond. Partial ion yields (PIY) of these ions for PTFE and PVDF thin films show strong photon energy dependencies near fluorine and carbon K-edges. The excitation from fluorine 1s to σ(C–F)* is specially efficient for F+ ion production for both PTFE and PVDF.