排序方式: 共有37条查询结果,搜索用时 31 毫秒
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Yi Chen Deng-Gao Chen Yi-An Chen Cheng-Ham Wu Kai-Hsin Chang Fan-Yi Meng Meng-Chi Chen Jia-An Lin Chun-Ying Huang Jianhua Su He Tian Prof. Pi-Tai Chou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16755-16764
With the aim of generalizing the structure–properties relationship of bending heterocyclic molecules that undergo prominent photoinduced structural planarization (PISP), a series of new dihydrodibenzo[ac]phenazine derivatives in which one nitrogen atom is replaced by oxygen ( PNO ), sulfur ( PNS ), selenium ( PNSe ), or dimethylmethanediyl ( PNC ) was strategically designed and synthesized. Compounds PNO , PNS , and PNSe have significantly nonplanar geometries in the ground state, which undergo PISP to give a planarlike conformer and hence a large emission Stokes shift. A combination of femtosecond early relaxation dynamics and computational approaches established an R*→I* (intermediate)→P* sequential kinetic pattern for PNS and PNSe , whereas PNO undergoes R*→P* one-step kinetics. The polarization ability of the substituted heteroatoms, which is in the order O<S<Se, correlates with their increase in π conjugation, and hence the Stokes shift of the emission is in the order PNO < PNS < PNSe . Compound PNSe with the largest PISP barrier was shown to be a highly sensitive viscosity probe. Further evidence for heteroatom-harnessing PISP is given by PNC , in which the dimethylmethanediyl substituent lacks lone pair electrons for π extension, showing the normal emission of the bent structure. The results led to the conclusion that PISP is ubiquitous in dihydrodibenzo[ac]phenazines, for which the driving force is elongation of the π delocalization to gain stabilization in the excited state. 相似文献
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Guangchen Sun Yu-Chen Wei Dr. Zhiyun Zhang Jia-An Lin Zong-Ying Liu Dr. Wei Chen Prof. Jianhua Su Prof. Pi-Tai Chou Prof. He Tian 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(42):18770-18777
Herein, we introduce the cyclic 8π-electron (C8π) molecule N,N′-diaryl-dihydrodibenzo[a,c]phenazine ( DPAC ) as a dual-functional donor to establish a series of new donor–linker–acceptor (D–L–A) dyads DLA1 – DLA5 . The excited-state bent-to-planar dynamics of DPAC regulate the energy gap of the donor, while the acceptors A1 – A5 are endowed with different energy gaps and HOMO/LUMO levels. As a result, the rate and efficiency of the excited-state electron transfer vs. energy transfer can be finely harnessed, which is verified via steady-state spectroscopy and time-resolved emission measurements. This comprehensive approach demonstrates, for the first time, the manifold of excited-state properties governed by bifunctional donor-based D–L–A dyads, including bent-to-planar, photoinduced electron transfer (PET) from excited donor to acceptor (oxidative-PET), fluorescence resonance energy transfer (FRET), bent-to-planar followed by electron transfer (PFET), and PET from donor to excited acceptor (reductive-PET). 相似文献
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Ping‐Lin Kuo Wei‐Fu Chen Wuu‐Jyh Liang 《Journal of polymer science. Part A, Polymer chemistry》2005,43(15):3359-3367
A new class of proton‐conducting polymer was developed via the sol–gel process from amino‐containing organic–inorganic hybrids by the treatment of poly(allylamine) with 3‐glycidoxypropyltrimethoxysilane doped with ortho‐phosphoric acid. The polymer matrix contains many hydrophilic sites and consists of a double‐crosslinked framework of polysiloxane and amine/epoxide. Differential scanning calorimetry results suggest that hydrogen bonding or electrostatic forces are present between H3PO4 and the amine nitrogen, resulting in an increase in the glass‐transition temperature of the poly(allylamine) chain with an increasing P/N ratio. The 31P magic‐angle spinning NMR spectra indicate that three types of phosphate species are involved in the proton conduction, and the motional freedom of H3PO4 is increased with increasing P/N ratios. The conductivity above 80 °C does not drop off but increases instead. Under a dry atmosphere, a high conductivity of 10?3 S/cm at temperatures up to 130 °C has been achieved. The maximum activation energy obtained at P/N = 0.5 suggests that a transition of proton‐conducting behavior exits between Grotthus‐ and vehicle‐type mechanisms. The dependence of conductivity on relative humidity (RH) above 50% is smaller for H3PO4‐doped membranes compared with H3PO4‐free ones. These hybrid polymers have characteristics of low water content (23 wt %) and high conductivity (10?2 S/cm at 95% RH), making them promising candidates as electrolytes for fuel cells. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3359–3367, 2005 相似文献
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Kuang-Yu Hu Jia-An Wuu Ming-Ching Kao Yu-Tien Liu Shou-Hsiung Pai 《Applied biochemistry and biotechnology》1998,73(2-3):231-241
Streptomyces chusanensis ZS-2, isolated from a soil sample in Chusan in Taiwan, was found to produce a new Type II restriction endonuclease. This
restriction enzyme was designated as SchI. The purified enzyme was characterized as having a subunit mol wt of 28 kDa, and
was apparently free from exonuclease activities. It cleaves the phosphodiester bond between the fourth C and the fifth G on
the 5’-CCGCGG-3’ sequence of DNAs, leaving a 2-nucleotide protruding end at its 3’ site. This data suggests that SchI is an
isoschizomer of SacII. In addition, based on the comparison between SchI and SacII regarding reaction parameters, it seems
that SchI is a better choice of restriction enzyme for genetic analysis and mapping. 相似文献
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设X为一(■t)特殊半鞅,X=A+M为其典则分解.称X有可料表示性,如果一切零初值(■t)局部鞅可表为一可料过程对M的随机积分.本文刻划了一类特殊半鞅的可料表示性(定理1.3及2.2);推广了Yoeurp-Yor定理(定理4.4).作为这些结果的应用,文中给出了Fujisaki-Kallianpur-Kunita定理的一个新证明(定理5.3). 相似文献
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以苯基二氯化膦和薄荷基甲酸为原料, 合成了一种手性双酰基膦氧化物光引发剂(-)-双(薄荷基甲酰基)苯基氧化膦. 采用核磁共振谱、 质谱及元素分析确定了该化合物的结构, 并测定了其螺旋诱导能力. 结果表明, (-)-BMPPO在引发自由基光聚合大位阻的单体甲基丙烯酸-1-苯基二苯并环庚酯(PDBSMA)的反应中具有螺旋选择性. 所得聚合物具有高度全同结构并显示出光学活性, 说明该聚合物形成了稳定的单手性螺旋链构象. 降低单体与引发剂的投料比及提高聚合温度有利于增加反应的螺旋选择性. 在手性薄荷醇溶剂中, 由(2,4,6-三甲基苯甲酰基)二苯基氧化膦(TPO)引发单体PDBSMA的光聚合反应也具有螺旋选择性, 但螺旋选择性很小. 相似文献
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5-硝基-6-羟基-2-(对甲氧羰基苯基)苯并噁唑的合成 总被引:1,自引:0,他引:1
研究了以关键中间体4-氨基-6-硝基间苯二酚盐酸盐(ANR·HCl)和对苯二甲酸单甲酯(MTA)为原料,分别经酰氯化、缩合、环合分步或原位合成AB型新单体前体--4-(5-硝基-6-羟基-2-苯并噁唑基)苯甲酸甲酯(MNB)的技术。 反应优化条件:在甲基异丁基酮溶剂中,n(ANR·HCl)∶n(MTA)=1.00∶1.03,115 ℃缩合反应2.5 h;m(ANR·HCl)∶m(PPA)=1.00∶3.25的多聚磷酸(PPA),120 ℃环合8.5 h;MNB收率75.68%(以ANR·HCl计),HPLC测定ω(MNB)=96.32%。 产物结构经1H NMR和IR确证。 相似文献
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R. H. Horng D. S. Wuu C. Y. Kung J. C. Lin C. C. Leu T. Y. Haung S. M. Sze 《Journal of Non》2001,280(1-3):48-53
The effects of ion implantation on the properties of spin-on sol–gel Ba0.7Sr0.3TiO3 (BST) thin films were studied by implanted Ar+, N+, and F+ doses. The F+-implanted BST samples present leakage current density <10−6 A/cm2 at 2.5 V and dielectric constant 450. The leakage current of F+-implanted BST samples was reduced about one order of magnitude as compared with that of samples with implanted Ar+, N+ or without implantation. The thickness shrinkage from 135 to 115 nm was observed in F+-implanted BST films (before annealing treatment) and a respective increase in the refractive index from 1.84 to 2.05 was measured. After annealing the implanted samples, the changes of thickness and refractive index depend on the concentration of implanted dose. Based on an infrared transmission study of the samples we suggest that the ion-implanted samples with smaller dose (5×1014 cm−2) have fewer −OH contaminants than the non-implanted or implanted samples with the larger doses (1×1015 cm−2). Based on the results presented, we conclude that suitable ion implantation densifies the spin-on sol–gel BST films and reduces the −OH contaminants in the films. 相似文献