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991.
Photophysical properties of porphyrin tapes 总被引:1,自引:0,他引:1
Cho HS Jeong DH Cho S Kim D Matsuzaki Y Tanaka K Tsuda A Osuka A 《Journal of the American Chemical Society》2002,124(49):14642-14654
The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso-meso, beta-beta, beta-beta positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, approximately 500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of approximately 1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from approximately 4.5 ps for the T2 dimer to approximately 0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes were observed to be in a sharp contrast to those of the orthogonal porphyrin arrays. The PPP-SCI calculated charge-transfer probability indicates that the lowest excited state of the porphyrin tapes (Tn) resembles a Wannier-type exciton closely, whereas the lowest excited state of the directly linked porphyrin arrays can be considered as a Frenkel-type exciton. Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials. 相似文献
992.
Molecular dynamics simulations of binary colloidal monolayers, i.e., monolayers consisting of mixtures of two different particle sizes, are presented. In the simulations, the colloid particles are located at an oil-water interface and interact via an effective dipole-dipole potential. In particular, the influence of the particle ratio on the configurations of the binary monolayers is investigated for two different relative interaction strengths between the particles, and the pair correlation functions corresponding to the binary monolayers are calculated. The simulations show that the binary monolayers can only form two-dimensional crystals for certain particle ratios, for example, 2:1, 6:1, etc., while, for example, for a particle ratio of 7:1 the monolayers are found to be in a disordered, glassy state. The calculations also reveal that in analogy to the Wigner lattice the configurations are very sensitive to the relative interaction strength between the particles but not to the absolute magnitude of the interaction strength, even when particle size effects are taken into account. Consequently, it is argued that a comparison between the calculated configurations and actual binary particle monolayer systems could provide useful information on the relative interaction strength between large and small particles. Possible mechanisms giving rise to disparities in the interaction strength between large and small particles are described briefly. 相似文献
993.
Zhiqiang Tao 《European Polymer Journal》2007,43(2):550-560
A novel fluorinated epoxy resin, 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane (BGTF), was synthesized through a four-step procedure, which was then cured with hexahydro-4-methylphthalic anhydride (HMPA) and 4,4′-diaminodiphenyl-methane (DDM). As comparison, a commercial available epoxy resin, bisphenol A diglycidyl ether (BADGE), cured with the same curing agents was also investigated. We found that the BGTF gave the exothermic starting temperature lower than BADGE no mater what kind of curing agents applied, implying the reactivity of the former is higher than the latter. The fully cured fluorinated BGTF epoxy resins have good thermal stability with glass transition temperature of 170-175 °C and thermal decomposition temperature at 5% weight loss of 370-382 °C in nitrogen. The fluorinated BGTF epoxy resins also showed the mechanical properties as good as the commercial BADGE epoxy resins. The cured BGTF epoxy resins exhibited improved dielectric properties as compared with the BADGE epoxy resins with the dielectric constants and the dissipation factors lower than 3.3 and dissipation 2.8 × 10−3, respectively, which is related to the low polarizability of the C-F bond and the large free volume of CF3 groups in the polymer. The BGTF epoxy resins also gave low water absorption because of the existence of hydrophobic fluorine atom. 相似文献
994.
Yi‐Zhen Tang Hao Sun Ya‐Ru Pan Xiu‐Mei Pan Rong‐Shun Wang 《International journal of quantum chemistry》2007,107(6):1495-1501
The mechanisms for the reaction of CH3S with NO2 are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero‐point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6‐311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6‐311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH3SONO and then dissociate to CH3SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
995.
Wei Sun Yan‐Tuan Li Zhi‐Yong Wu Ning‐Yu Xiao 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(3):m111-m113
In the crystal structure of the title complex, [Ni2(C10H20N4O2)(C12H12N2)2](ClO4)2 or [Ni(dmaeoxd)Ni(dmbp)2](ClO4)2 {H2dmaeoxd is N,N′‐bis[2‐(dimethylamino)ethyl]oxamide and dmbp is 4,4′‐dimethyl‐2,2′‐bipyridine}, the deprotonated dmaeoxd2− ligand is in a cis conformation and bridges two NiII atoms, one of which is located in a slightly distorted square‐planar environment, while the other is in an irregular octahedral environment. The cation is located on a twofold symmetry axis running through both Ni atoms. The dmaeoxd2− ligands interact with each other via C—H⋯O hydrogen bonds and π–π interactions, which results in an extended chain along the c axis. 相似文献
996.
Yan-Ping Liu Li-Li Sun Xiang-Lin Zhang Hai-Yuan Niu Zheng-Hong Pan 《Natural product research》2020,34(16):2295-2300
Abstract A phytochemical investigation on the stems of Mappianthus iodoides led to the isolation of a new naturally occurring prenylated isoflavone, mappianthone A (1), together with seven known analogues (2?8). The structure of 1 was elucidated by extensive spectroscopic methods and the known compounds were identified by comparison with data reported in the literature. All isolated compounds were evaluated for their antiproliferative activities against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480 in vitro. Compounds 1?8 showed significant antiproliferative effects against several human cancer cell lines with IC50 values ranging from 0.16 to 12.68?μM. 相似文献
997.
Synthesis and reactivity of 3-(trichlorogermyl)propanoic acid and 3-(triphenylgermyl) propanoic acid
3-(Trichlorogermyl)propanoic acid (la) reacts with phenylmagnesium bromide in malar ratio 1:4 to give 3-(triphenylgermyl)propanoic acid (2a).In the compounds la and 2a theβ-carboxylic functional group shows some unusual properties when they react with excess of phenylmagnesium bromide.The compound la reacts with phenylmagnesium bromide in molar ratio 1:5 to give phenyl 2-(triphenylgermyl)ethylketone (3a) and in molar ratio 1:6 to give l,l-diphenyl-3-(triphenylgermyl)propanol (4a).The compound 2a reacts with phenylmagnesium bromide in molar ratio 1:2 to give 3a and in molar ratio 1:3 to give 4a also.Dehydration of the compound 4a with dilute hydrochloric acid seems especially easy.Moreover,the compound la reacted with phenylmagnsium bromide in molar ratio 1:6,then the mixture was treated with dilute hydrochloric acid to give 1,1-diphenyl-3-(triphenylgermyl)-1-propene (5a) in one pot reaction.Alkyl Ge-C bond in the compound 5a can be cleaved selectively by lithium aluminium hydride ( LiAlH4) in good yiel 相似文献
998.
Wang Xiaolin Chen Yinliang Wang Xiuyuan Sun Ying Fu Yibei Guo Gaopin 《Journal of Radioanalytical and Nuclear Chemistry》1991,147(2):377-384
A method of determination of trace gold and iridium in steel is presented. The samples were preconcentrated with an anion exchanger. The chemical recoveries were determined by an isotope tracer technique using198Au and192Ir. 相似文献
999.
The preconcentration and voltammetric behavior of BiIII on a sodium humate modified carbon paste electrode was studied by means of cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). The proposed measurement involves an initial nonelectrolytic preconcentration step in which BiIII is complexed by the surface modifier in a solution of 0.05 M KNO3-0.0106 M HNO3 (pH 2.0) and a subsequent electrochemical scan step in which the preconcentrated BiIII was reduced and then oxidized promptly in supporting electrolyte of 0.5 M HNO3. The resulting DPSV anodic current was proportional to the concentration of BiIII ion over the range of 4.78 × 10−8–1.44 × 10−5 M. The detection limit was 4.78 × 10−8 M. The proposed method was used to determine bismuth in various samples. Various factors affecting the electrode behavior were also investigated at the same time. 相似文献
1000.