Mitsuo Kawasaki

Light Harvesting and Energy Transfer in Multiporphyrin‐Modified CdSe Nanoparticles

Multiporphyrin-modified CdSe nanoparticles (CdSe-H2P) were prepared to elucidate the interaction between chromophores and luminescent semiconducting nanoparticles in the excited and ground states. The CdSe-H2P nanoparticles were obtained by place-exchange reactions of hexadecylamine-thiophenol-modified CdSe nanoparticles with porphyrin alkanethiols in toluene. The number of porphyrin molecules on the surface of a single CdSe nanoparticle increased with increasing reaction time to reach a saturated maximum of 21. The porphyrins as well as the core in CdSe-H2P can absorb UV/Vis radiation. Steady-state emission and emission-lifetime measurements reveal efficient energy transfer from the CdSe excited state to the porphyrins in the CdSe-H2P nanoparticles. The resulting porphyrin excited singlet state is not quenched by the CdSe core. These unique properties are in sharp contrast with those of multiporphyrin-modified metal and silica nanoparticles. Thus, semiconducting nanoparticle-multiporphyrin composites are highly promising as novel artificial photosynthetic materials.

Contribution of low-energy ion bombardment to the growth of atomically flat Ag(111) and Au(111) films by glow discharge sputtering

Abstract Atomically flat Ag(111) and Au(111) films grow relatively easily by simple DC glow-discharge sputtering. A series of sputter deposition experiments on deliberately DC-biased samples illuminated the important contribution of low-energy ion bombardment leading to the superior surface flatness of the sputtered films. Smoothest films grew at around the floating potential, where the Ar+ ions impinge upon the growing film surface with maximum allowed kinetic energies of several electron volts and with an ion flux comparable to that of incoming metal atoms. It is proposed that such a low-energy ion bombardment leads to a substantial enhancement of the interlayer mass transport across the step edges on atomically terraced surfaces.

Sputter deposition of atomically flat Au(111) and Ag(111) films

Abstract A simple Ar-ion sputter deposition has allowed preparation of atomically flat Au(111) and Ag(111) films in conditions of much lower substrate temperature and/or deposition rate compared with vacuum deposition. At a deposition rate less than 1 A s−1, Au(111) films with extended terrace structures could be grown on a freshly cleaved and heated mica (∼300°C) without extensive substrate prebaking. Sputtered Ag(111) films could also be grown atomically flat at a similar deposition rate, preferably on Au(111) predeposited on mica. Particularly smooth Ag(111) films often accompanied by hexagonal faceting grew at substrate temperatures, 150–200°C, near the point at which serious clouding of the film surface set in.

Atmospheric degradation mechanism of CF3OCF2H

A smog chamber/FTIR technique was used to study the Cl atom initiated oxidation of CF3OCH3 in 700 Torr of N2/O2 at 296 K. Using relative rate techniques it was determined that k(Cl + CF3OCH3) = (1.4 ± 0.2) × 10-13 and k(Cl + CF3OC(O)H) = (9.8 ± 1.2) × 10-15 cm3 molecule-1 s-1. At 700 Torr of N2/O2 diluent at 296 K reaction with O2 is the only loss mechanism of the CF3OCH2O• radical. The infrared spectra of the peroxy nitrates CF3OCH2O2NO2 and CF3OC(O)O2NO2 were recorded and compared to the nonfluorinated analogues CH3OCH2O2NO2 and CH3OC(O)O2NO2. The thermal decomposition rate of CF3OC(O)O2NO2 is (2.3 ± 0.1) × 10-4 s-1 in 700 Torr of N2 at 295.8 K. The reaction of CF3OC(O)O2 radicals with HO2 radicals gives CF3OC(O)H in a yield of (80 ± 11)%. The results are discussed with respect to the atmospheric degradation mechanism of CF3OCH3 and other ethers.

Transfer of photoelectrons and photoholes through a AgBr/AgCl interface, and relative locations of the energy bands

The transfer of photoelectrons and photoholes through the interface between AgBr and AgCl thin‐sheet crystals was studied by the transient dc pulse method. Photoelectrons were transferred very easily with near perfect freedom in both directions from AgBr to AgCl and from AgCl to AgBr. The photohole transfer, however, was allowed only from AgCl to AgBr, and the transfer from AgBr to AgCl was effectively blocked at the interface. These results were carefully analyzed in terms of the relative locations of the energy bands of AgBr and AgCl. It was concluded that the bottom of conduction band of AgBr was likely to lie very close to that of AgCl, while the top of valence band of AgBr was separated from that of AgCl by an amount nearly equal to the difference in the band‐gap energies of AgBr and AgCl.

Facile Carbon Fixation to Performic Acids by Water-Sealed Dielectric Barrier Discharge

Carbon fixation refers to the conversion of carbon dioxide (CO2) to organic materials, as commonly performed in nature through photosynthesis by plants and other autotrophic organisms. The creation of artificial carbon fixation processes is one of the greatest challenges for chemistry to solve the critical environmental issue concerning the reduction of CO2 emissions. We have developed an electricity-driven facile CO2 fixation process that yields performic acid, HCO2OH, from CO2 and water at neutral pH by dielectric barrier discharge with an input electric power conversion efficiency of currently 0.2−0.4%. This method offers a promising future technology for artificial carbon fixation on its own, and may also be scaled up in combination with e.g., the post-combustion CO2 capture and storage technology.

High efficiency photocurrent generation by two-dimensional mixed J-aggregates of cyanine dyes

Two-dimensional mixed J-aggregates of structurally and spectrally analogous anionic cyanine dyes, coadsorbed on a self-assembled monolayer of aminoalkanethiolate on Au(111), generated a high-efficiency (20-30% quantum efficiency) cathodic photocurrent and a significant photovoltaic effect in reversible Fe2+/Fe3+ redox solution.

Kinetics and mechanism of the gas phase reaction of Cl atoms and OH radicals with bromobenzene

Abstract Relative rate techniques were used to study the kinetics and mechanism of the reaction of Cl atoms and OH radicals with bromobenzene (C 6 H 5 Br) in 20–700 Torr of N 2 , O 2 , or air diluent at 295±2 K. Using the observed rate constant ratios k (C 6 H 5 Br+Cl)/ k (C 2 H 5 Cl+Cl)=1.56±0.05 and k (C 6 H 5 Br+Cl)/ k (C 2 H 6 +Cl)=0.24±0.01, the C 6 H 5 Br+Cl rate constant is determined to be k( C 6 H 5 Br + Cl )=(1.32±0.20)×10 −11 cm 3 molecule −1 s −1 giving exclusively C 6 H 5 Cl through a displacement mechanism. Using the observed rate constant ratios k (C 6 H 5 Br+OH)/ k (C 6 H 6 +OH)=0.77±0.06 and k (C 6 H 5 Br+OH)/ k (C 2 H 4 +OH)=0.11±0.004, the C 6 H 5 Br+OH rate constant is determined to be k( C 6 H 5 Br + OH )=(9.37±2.04)×10 −13 cm 3 molecule −1 s −1 . The product expected from a displacement mechanism, phenol, was not observed (

Measurement of the lifetime of silver atoms on silver bromide grain surfaces in photographic emulsion by the multiflash method

The multiflash exposure method, which is a new useful and powerful tool for studying the nature of the photolytic silver atom on silver halide grain surface, is reported. The lifetime of the photolytic silver atom and the corresponding activation energy are easily and quantitatively determined by this method. The lifetime at 20 °C and the apparent activation energy were 1.1 s and 0.7 eV, respectively, on (100) surface of a chemically unsensitized silver bromide grain in a wet air environment. In a vacuum environment the lifetime was prolonged to 300 s and the activation energy was decreased to 0.40 eV.

Good solvent effects of C70 cluster formations and their electron-transporting and photoelectrochemical properties.

Good solvent effects of C(70) cluster formations and their electron-transporting and photoelectrochemical properties have been systematically examined for the first time. Nano-to-micrometer scale assemblies of C(70) with different morphologies were prepared by rapidly injecting poor solvent (i.e., acetonitrile) into a solution of C(70) dissolved in various good solvents (i.e., benzene, toluene, chlorobenzene, etc). The cluster morphology engineering was successfully achieved by changing the good solvent, yielding the spherical, rodlike, or platelike clusters in the mixed solvents. The clusters of C(70) were electrophoretically deposited onto a nanostructured SnO(2) electrode to examine the photoelectrochemical properties under the white light or monochromatic light illumination. The maximum incident photon-to-current efficiency (IPCE) varied from 0.8 to 10% depending on the combinations of the poor-good solvents. The differences in the IPCE values are discussed in terms of the surface area, thickness, and electron mobility of the deposited cluster films. The electron mobility is found to be the most predominant factor for the IPCE, indicating the importance of the electron-transporting process in the overall photocurrent generation. In addition, the electron mobility is closely correlated with the underlying molecular alignment and the resultant cluster structure. Thus, these results will provide basic clue for the design of C(70)-based molecular devices including the organic photovoltaics.