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排序方式: 共有534条查询结果,搜索用时 93 毫秒
51.
K. Mizuno T. Matsubara K. Sugahara M. Ichida H. Ando T. Itoh 《Journal of luminescence》2011,131(3):506-509
A persistent hole-burning is observed in β-perylene microcrystallites, which were embedded in poly-vinyl alcohol. By laser light excitation at 22,535 cm−1 and at 10 K, the hole is found at the excitation photon energy. The mechanism of the persistent hole-burning is interpreted in terms of the resolution of microcrystallites into smaller microcrystallites. This is a novel observation of the persistent hole-burning in aromatic microcrystallites. When the specimen, which includes a hole, is annealed at high temperatures, the resolved microcrystallites restore back to the old position as had been. The β-perylene microcrystallite specimen that we have grown was as small as 1.5 nm in average diameter. They are one order smaller in number of molecules included, compared to those that have been reported on aromatic microcrystallites, anthracene for example. Due to this, we were able to observe the 0-0 transition energy, which varied according as the number of molecules involved in the microcrystallites. We also observed the 0-0 absorption (excitation) spectrum, which depends on the molecular arrays in the microcrystallites. The 0-0 transition of a single molecule in poly-vinyl alcohol matrix is anticipated to be located at 22,885 cm−1. 相似文献
52.
Masayuki Nogami Shohei Hotta Kazumasa Kugimiya Hideaki Matsubara 《Journal of Sol-Gel Science and Technology》2010,56(2):107-113
Silica-based aerogels with high transparency and high bending strength were prepared using methyltrimethoxysilane and non-ionic
surfactant under supercritical drying condition of CO2. Non-ionic surfactant, ethylene oxide/propylene oxide block copolymer, was appropriate to form the three dimensional-connected
thinner fibers of silica skeletons, which was extruded by soaking the wet gel in hot water at 50 °C, resulting in the formation
of porous materials having small pores with narrow size distribution. The transparency of aerogels increased with decreasing
the pore size, reaching to higher than 65 and 88% at 400 and 600 nm wavelength, respectively, for 10 mm thickness of sample.
The formation of fiber skeletons were discussed using small angle X-ray scattering experiments. 相似文献
53.
Phosphorylimidates reacted with N-Boc imines in the presence of a catalytic amount of potassium hexamethyldisilazide, to afford the corresponding Mannich-type adducts in high yields. It was shown that, like sulfonylimidates, phosphorylimidates can function as ester equivalents. In contrast to sulfonylimidates however, phosphorylimidates exhibited high anti-selectivity even in low polar solvents. An explanation for the anti-selectivity is given. 相似文献
54.
55.
A Triphenylamine with Two Phenoxy Radicals Having Unusual Bonding Patterns and a Closed‐Shell Electronic State 下载免费PDF全文
Dr. Daisuke Sakamaki Soichiro Yano Toshiyuki Kobashi Prof. Dr. Shu Seki Dr. Takuya Kurahashi Prof. Dr. Seijiro Matsubara Dr. Akihiro Ito Prof. Dr. Kazuyoshi Tanaka 《Angewandte Chemie (International ed. in English)》2015,54(28):8267-8270
Reported herein is the structure and the electronic properties of a novel triphenylamine derivative having two phenoxy radicals appended to the amino nitrogen atom. X‐ray single crystal analysis and the magnetic resonance measurements demonstrates the unexpected closed‐shell electronic structure, even at room temperature, of the molecule and two unusual C? N bonds with multiple‐bond character. The theoretical calculations support the experimentally determined molecular geometry with the closed‐shell electronic structure, and predicted a small HOMO–LUMO gap originating from the nonbonding character of the HOMO. The optical and electrochemical measurements show that the molecule has a remarkably small HOMO–LUMO gap compared with its triphenylamine precursor. 相似文献
56.
Naoki Yoneda Yukihiro Fukata Dr. Keisuke Asano Prof. Dr. Seijiro Matsubara 《Angewandte Chemie (International ed. in English)》2015,54(51):15497-15500
Chiral spiroketal skeletons are found as core structures in a range of bioactive compounds. These natural compounds and their analogues have attracted much attention in the field of drug discovery. However, methods for their enantioselective construction are limited, and easily available optically active spiroketals are rare. We demonstrate a novel catalytic asymmetric synthesis of spiroketal compounds that proceeds through an intramolecular hemiacetalization/oxy‐Michael addition cascade mediated by a bifunctional aminothiourea catalyst. This results in spiroketal structures through the relay formation of contiguous oxacycles, in which multipoint recognition by the catalyst through hydrogen bonding imparts high enantioselectivity. This method offers facile access to spiroketal frameworks bearing an alkyl group at the 2‐position, which are prevalent in insect pheromones. Optically active (2S,5S)‐chalcogran, a pheromone of the six‐spined spruce bark beetle, and an azide derivative could be readily synthesized from the bicyclic reaction product. 相似文献
57.
Komal Garg Yasuo Matsubara Mehmed Z. Ertem Anna Lewandowska‐Andralojc Shunsuke Sato David J. Szalda James T. Muckerman Etsuko Fujita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(47):14334-14338
We prepared two geometric isomers of [Ir(tpy)(ppy)H]+, previously proposed as a key intermediate in the photochemical reduction of CO2 to CO, and characterized their notably different ground‐ and excited‐state interactions with CO2 and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]+, reacts with CO2 to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH3CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]0 species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO2 and produces CO with the same catalytic efficiency. 相似文献
58.
A.?Inasawa F.?LundellEmail author M.?Matsubara Y.?Kohama P.?H.?Alfredsson 《Experiments in fluids》2003,34(2):242-252
It is known from smoke visualizations that in a transitional boundary layer subjected to free-stream turbulence, streaks appear
and eventually break down to turbulence after wavy motions. In order to observe the streaky structures directly, a stereo
particle-tracking velocimetry system using hydrogen bubbles in a water channel has been developed and validated against laser
Doppler velocimetry. Mean flow statistics show good agreement with previous results. With the developed measurement system,
the instantaneous spanwise distribution of the streamwise and wall-normal velocities can be measured fast enough to resolve
the time development of the streaky structures. Measurements of instantaneous spanwise distributions of the streamwise and
wall-normal velocity disturbances show strong negative correlation between the wall-normal and streamwise velocities in the
streaks.
Published online: 19 November 2002 相似文献
59.
Mutsumi SadaSeijiro Matsubara 《Tetrahedron》2011,67(14):2612-2616
An alkylation to an easily enolizable ketone, such as β-tetralone, is difficult to perform with Grignard reagent (RMgX) or with diorganomagnesium (R2Mg), because a deprotonation to form a magnesium enolate occurs predominantly. To avoid the prior enolization, a complex reagent of a transition-metal salt and R2Mg was examined: A combination of R2Mg with iron(II) chloride (FeCl2) or ytterbium(III) chloride (YbCl3) gave a complex reagent that can realize a nucleophilic reaction to β-tetralone prior to the enolization. A combination of RMgX with these metal salts is inferior to a combination of R2Mg with them to obtain the nucleophilic complex reagent. 相似文献
60.