Time-resolved fluorescence of α-(9-anthryl)-ω-(1-naphthyl)-oligosilanes: intramolecular electronic energy and charge transfer through π-π and σ-π interactions

The photophysical properties of a series of α,ω-diaryloligosilanes: (9-anthryl)-(SiMe₂)_n-(1-naphthyl) (1-4, and 6), n=1, 2, 3, 4, and 6, were investigated. For n?2, the intramolecular exciplex emission was observed in cyclohexane. For the stationary and the time-resolved fluorescence (TR-FL) measurements, the excitation of the naphthyl moiety showed a very efficient intramolecular energy transfer to the anthryl moiety, thus only fluorescence from the anthryl moiety was observed. In the case of 4 and 6, a charge-transfer (CT) emission was observed in acetonitrile. Then TR-FL of 6 revealed that the intramolecular-energy transfer from the naphthyl to anthryl moieties is faster than the CT.     

Electrical resistance of a monatomic step on a crystal surface

We have succeeded in measuring the resistance across a single atomic step through a monatomic-layer metal on a crystal surface, Si(111)(sqrt[3]xsqrt[3])-Ag, using three independent methods, which yielded consistent values of the resistance. Two of the methods were direct measurements with monolithic microscopic four-point probes and four-tip scanning tunneling microscope probes. The third method was the analysis of electron standing waves near step edges, combined with the Landauer formula for 2D conductors. The conductivity across a monatomic step was determined to be about 5 x 10(3) Omega(-1) m(-1). Electron transport across an atomic step is modeled as a tunneling process through an energy-barrier height approximately equal to the work function.     

Construction of positively-charged layered assemblies assisted by cyclodextrin complexation

A beta-cyclodextrin dimer is found to be effective in preparing a layer-by-layer architecture of positively charged ferrocene-appended poly(allylamine) presumably on the basis of strong beta-cyclodextrin-ferrocene host-guest interaction.     

X-ray diffraction profiles of Si nanowires with trapezoidal cross-sections

Comparisons of the experimental and calculated X-ray diffraction profiles have been made for Si nanowires with trapezoidal cross-sections. Examined samples are periodically arranged nanowires prepared on a silicon-on-insulator wafer by electron-beam lithography, so that they are isolated from Si substrate. The nanowire periodicity gives rise to diffractions at additional reciprocal lattice points, which we employ to avoid the mixture of the diffraction from the Si substrate. The experimental diffraction profiles are found to be in good agreement with the square modulus of the Fourier transform of the trapezoidal cross-sections determined from transmission electron micrographs.     

Clarithromycin form I determined by synchrotron X‐ray powder diffraction

The structure of the metastable form I polymorph of the macrolide antibiotic clarithromycin, C₃₈H₆₉NO₁₃, was determined by a powder diffraction method using synchrotron radiation. The space group of form I is P2₁2₁2. The initial model was determined by a molecular replacement method using the structure of clarithromycin form 0 as a search model, and the final structure was obtained through Rietveld refinements. In the form I crystal structure, the clarithromycin molecules are aligned parallel along the a axis in a head‐to‐tail manner with intermolecular hydrogen bonds between the hydroxy O atoms. The dimethylamine groups of the clarithromycin molecule interdigitate between neighbouring head‐to‐tail clarithromycin alignments. The novel crystal packing found in form I provides a mechanism that describes the transformation of form 0 to form I.     

Neutral-fermionic presentation of the K-theoretic Q-function

Journal of Algebraic Combinatorics - We show a new neutral-fermionic presentation of Ikeda-Naruse’s K-theoretic Q-functions, which represent a Schubert class in the K-theory of coherent...     

Copolymerization of Chloroprene with Methyl Methacrylate by the EtnAICI3.n (n=1, 1.5, 2)-Vanadium Compound System

Abstract

The copolymerization of chloroprene with methyl methacrylate was studied in the presence of Et_n A1C1_3-n (n=1, 1.5, 2)-vanadium compounds. Monomer reactivity ratios in various catalyst concentrations were compared with that of a usual radical initiator. The apparent monomer reactivity ratio changed with the concentration of alkylaluminum halide. In this polymerization, alternating copolymer could not be prepared by the ordinary catalyst concentration by which the alternating copolymerization of chloroprene with acrylonitrile was carried out. The addition of more than 10 mole % of the alkylaluminum halide based on two monomers was required to prepare the copolymer which had equimolar composition irrespective of the feed monomer ratio.

The configuration in the repeating unit of the copolymer was discussed by comparison with the NMR and IR spectra of the radical copolymer and the cyclic Diels-Alder adduct of chloroprene-methyl methacrylate. The high alternating tendency was clarified by ozonolysis of the copolymer which was prepared under the conditions which produced equimolar copolymer in various feed monomer ratios. The chloroprene unit of the copolymer was present in the 1, 4-trans structure in the copolymer prepared by the Et_n A1C1_3-n -vanadium compound system.     

1‐Aryl‐4‐Silylmethyl[60]fullerenes: Synthesis,Properties, and Photovoltaic Performance

The efficient nucleophilic addition of aryl Grignard reagents (aryl=4‐MeOC₆H₄, 4‐Me₂NC₆H₄, Ph, 4‐CF₃C₆H₄, and thienyl) to C₆₀ in the presence of DMSO produced 1,2‐arylhydro[60]fullerenes after acid treatment. The reactions of the anions of these arylhydro[60]fullerenes with either dimethylphenylsilylmethyl iodide or dimethyl(2‐isopropoxyphenyl)silylmethyl iodide yielded the target compounds, 1‐aryl‐4‐silylmethyl[60]fullerenes. The properties and structures of these 1‐aryl‐4‐silylmethyl[60]fullerenes (aryl=4‐MeOC₆H₄, thienyl) were examined by electrochemical studies, X‐ray crystallography, flash‐photolysis time‐resolved microwave‐conductivity (FP‐TRMC) measurements, and electron‐mobility measurements by using a space‐charge‐limited current (SCLC) model. Organic photovoltaic devices with a polymer‐based bulk heterojunction structure and small‐molecule‐based p–n and p–i–n heterojunction configurations were fabricated by using 1‐aryl‐4‐silylmethyl[60]fullerenes as an electron acceptor. The most efficient device exhibited a power‐conversion efficiency of 3.4 % (short‐circuit current density: 8.1 mA/ cm², open‐circuit voltage: 0.69 V, fill factor: 0.59).     

Study on selective adsorption of deuterium on boron nitride using photon-stimulated ion-desorption

Adsorption behavior of atomic deuterium on a hexagonal boron nitride (h-BN) thin film is studied by photon-stimulated ion desorption (PSID) of D⁺ and near edge X-ray absorption fine structure (NEXAFS) at the B and N K-edges. After the adsorption of atomic deuterium, D⁺ desorption yield η(hν) shows clear enhancement at the B K-edge and almost no enhancement at the N K-edge. NEXAFS spectra show a large change in the B K-edge and a small change in the N K-edge after the adsorption. We propose selective adsorption of atomic deuterium on the h-BN thin film based on the experimental results, and mention the effectiveness of applying the PSID method with X-ray to study hydrogen storage materials.     

EXCITATION ENERGY TRANSFER IN THE CHROMATICALLY ADAPTED PHYCOBILIN SYSTEMS OF BLUE-GREEN ALGAE: DIFFERENCE IN THE ENERGY TRANSFER KINETICS AT PHYCOCYANIN LEVEL

Abstract— Excitation energy transfer in chromatically adapted phycobilin system was investigated with the blue-green algae Tolypothrix tenuis and, supplementary, Fremyella diplosiphon with use of time-resolved fluorescence spectrum (Yamazaki et al , 1984). Special attention was paid to the energy migration at the phycocyanin (PC) level in the phycoerythrin (PE)-rich and PE excited system and in the PE-less and PC excited system. The energy transfer from PC to allophycocyanin was far faster in the former than in the latter in both organisms. Such feature was the same as our previous observation for PE-rich system of Porphyridium cruentum and PE-less system of Anacystis nidulans (Yamazaki et al , 1984). Thus, the difference in phycobilisome structure is not a cause for such difference. Based on simulation analysis, we interpreted our observation as that (1) all PC chtomophores do not equally participate to the energy migration within PC compartment but (2) a short transfer path through PC compartment is formed probably by f-type chromophores and (3) the difference in the "length" of this path is a main determinant for kinetic difference between PE-rich and PE-less systems.