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Dr. Seiichi Uchiyama Kohki Kimura Chie Gota Dr. Kohki Okabe Kyoko Kawamoto Dr. Noriko Inada Dr. Toshitada Yoshihara Prof. Seiji Tobita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(31):9552-9563
An environment‐sensitive fluorophore can change its maximum emission wavelength (λem), fluorescence quantum yield (Φf), and fluorescence lifetime in response to the surrounding environment. We have developed two new intramolecular charge‐transfer‐type environment‐sensitive fluorophores, DBThD‐IA and DBSeD‐IA, in which the oxygen atom of a well‐established 2,1,3‐benzoxadiazole environment‐sensitive fluorophore, DBD‐IA, has been replaced by a sulfur and selenium atom, respectively. DBThD‐IA is highly fluorescent in n‐hexane (Φf=0.81, λem=537 nm) with excitation at 449 nm, but is almost nonfluorescent in water (Φf=0.037, λem=616 nm), similarly to DBD‐IA (Φf=0.91, λem=520 nm in n‐hexane; Φf=0.027, λem=616 nm in water). A similar variation in fluorescence properties was also observed for DBSeD‐IA (Φf=0.24, λem=591 nm in n‐hexane; Φf=0.0046, λem=672 nm in water). An intensive study of the solvent effects on the fluorescence properties of these fluorophores revealed that both the polarity of the environment and hydrogen bonding with solvent molecules accelerate the nonradiative relaxation of the excited fluorophores. Time‐resolved optoacoustic and phosphorescence measurements clarified that both intersystem crossing and internal conversion are involved in the nonradiative relaxation processes of DBThD‐IA and DBSeD‐IA. In addition, DBThD‐IA exhibits a 10‐fold higher photostability in aqueous solution than the original fluorophore DBD‐IA, which allowed us to create a new robust molecular nanogel thermometer for intracellular thermometry. 相似文献
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The vapor-liquid and liquid-liquid equilibria of binary mixtures formed by sulphur dioxide with organic components are reproduced well using a new associated-solution model whose association and solvation constants are defined in terms of the modified segment fractions of chemical species. The model shows a good performance in predicting ternary vapor-liquid and liquid-liquid equilibria of sulphur dioxide mixtures from only binary parameters. 相似文献
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Dr. Takuji Kawamoto Kohki Noguchi Ryotaro Takata Rio Sasaki Prof. Dr. Hiroshi Matsubara Prof. Dr. Akio Kamimura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(37):9529-9534
The redox-neutral tetrafluoroethylation of alkynes with 1,1,2,2-tetrafluroroethanesulfonic acid (TFESA) and azobis(isobutyronitrile) (AIBN) proceeds via the formation of vinyl tetrafluoroethanesulfonates followed by a radical tetrafluoroethylation. Experimental and theoretical results support an intermolecular reaction. 相似文献
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Tomoyuki Akiyama Haruhiko Kuwatsuka Takashi Simoyama Yoshiaki Nakata Kohki Mukai Mitsuru Sugawara Osamu Wada Hiroshi Ishikawa 《Optical and Quantum Electronics》2001,33(7-10):927-938
Ultrafast gain dynamics in quantum-dot optical amplifiers has been studied by using the pump-probe and four-wave mixing (FWM) techniques. It was found that there are at least three nonlinear processes, which are attributed to carrier relaxation to the ground states, phonon scattering, and carrier capture from the wetting layers into the quantum dots (QDs). The relevant time constants were evaluated to be ~90 fs, ~260 fs, and ~2 ps, respectively, under a 50 mA bias condition. The compressed gain recovered to 3% of its initial value in 4 ps, and no recovery component slower than 2 ps could be seen in the temporal range tested. This is quite different from the feature in quantum wells, where a very slow component (> 50 ps) exists. This suggests a possibility of enhancing the operation speed of semiconductor optical amplifiers by using QDs as an active layer. The third-order optical susceptibility (χ(3)) has been evaluated by means of both nonlinear transmission and FWM experiments. The results show that the nonlinearity expressed by χ(3)/g 0 is quite similar to that of bulk and quantum wells, which can be explained by the similar relaxation times. 相似文献
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Kinetics and Mechanism of the Racemization of Aryl Allenes Catalyzed by Cationic Gold(I) Phosphine Complexes
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Robert J. Harris Kohki Nakafuku Prof. Ross A. Widenhoefer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12245-12254
The kinetics of the racemization of aromatic 1,3‐disubstituted allenes catalyzed by gold phosphine complexes has been investigated. The rate of gold‐catalyzed allene racemization displayed first‐order dependence on allene, and catalyst concentration and kinetic analysis of gold‐catalyzed allene racemization as a function of allene and phosphine electron‐donor ability established the accumulation of electron density on the phosphine atom and the depletion of electron density on the terminal allenyl carbon atoms in the rate‐limiting transition state for racemization. These and other observations were in accord with a mechanism for allene racemization involving rapid and reversible inter‐ and intramolecular allene exchange followed by turnover‐limiting, unimolecular conversion of a chiral gold η2‐allene complex to an achiral η1‐allylic cation intermediate through a bent and twisted η1‐allene transition state. With respect to proper ligand selection, these studies reveal that both electron‐poor phosphine ligands and polar solvents facilitate racemization. 相似文献
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Yuichiro Haramoto Yuko Kawada Atushi Mochizuki Masato Nanasawa Seiji Ujiie Masahiro Funahashi Kohki Hiroshima Takamasa Kato 《Liquid crystals》2005,32(7):909-912
We report a new possibility for liquid crystalline organic semiconductors. These materials exhibit smectic liquid crystalline phases, in which the molecules assume a smectic molecular order by self-assembly. Because of the strong dispersion force among long alkyl chains, on cooling, smectic molecular order was retained at room temperature. A charge transport ability was also retained. The conductivity of a device having smectic liquid crystalline order is about 5×107 that of a device with no smectic order. The current - voltage characteristic of the device has a very sharp increase at low threshold voltage (5 V). A high carrier mobility of 1.8×10-2 was observed in the smectic phase of one of the compounds studied (e). 相似文献