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41.
Cheng YM Pu SC Yu YC Chou PT Huang CH Chen CT Li TH Hu WP 《The journal of physical chemistry. A》2005,109(51):11696-11706
Comprehensive excitation behaviors of 7-N,N-diethylamino-3-hydroxyflavone (I) have been investigated via steady state, temperature-dependent emission, and fluorescence upconversion to probe the excited-state intramolecular proton transfer (PT) reaction. Upon excitation, I undergoes ultrafast (<120 fs), adiabatic type of charge transfer (CT), so that the dipolar vector in the Franck-Condon excited state is much different from that in the ground state. In polar solvents such as CH2Cl2 and CH3CN, early relaxation dynamics clearly reveals the competitive rates between solvent relaxation and PT dynamics. After reaching thermal equilibrium, a relatively slow, solvent-polarity-dependent rate (a few tens of picoseconds(-1)) of PT takes places. Firm support of the early relaxation dynamics is rendered by the spectral temporal evolution, which resolves two distinct bands ascribed to CT and PT emission. The results, in combination with ab initio calculations on the dipolar vectors for various corresponding states, led us to conclude that excited-state normal (N*) and excited proton-transfer tautomer (T*) possesses very different dipole orientation, whereas the dipole orientation of the normal ground state (N) is between that of N* and T*. PT is thus energetically favorable at the Franck-Condon excited N*, and its rate is competitive with respect to the solvent relaxation dynamics induced by CT. Unlike the well-known PT system, 4'-N,N-diethylamino-3-hydroxyflavone, in which equilibrium exists between solvent-equilibrated N(eq)* and T(eq)*, N(eq)* --> T(eq)* PT for I is a highly exergonic, irreversible process in all solvents studied. Further temperature-dependent studies deduce a solvent-polarity-perturbed energy barrier of 3.6 kcal/mol for the N(eq)* --> T(eq)* PT in CH3CN. The proposed dipole-moment-tuning PT mechanism with the associated relaxation dynamics is believed to apply to many PT molecules in polar, aprotic solvents. 相似文献
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Macrocyclic Schiff‐base ligand, bisacetylaceton‐ethylenediimine (BAE) and its transition metal complexes M(BAE) (M = Cu2+, Ni2+) were synthesized. The complexes having characteristics of aromatic systems and well‐defined one‐dimensional structures, reacted with p‐phthaloyl chloride, to obtain polymer complexes. The complexes were characterized by elemental analysis, inductively coupled plasma (ICP), FT‐IR, and thermal analysis and show good thermal stability. ESR spectra analysis discovered that there are free radicals in the chain of polymers, indicating that a weak magnetic spin‐exchange interaction operates between the metal ions and free radicals. It is found that, as the bridging p‐phthaloyl group is able to propagate the magnetic exchange interaction, the polymer complexes show paramagnetic properties by measurement of temperature dependence of the magnetic property, and obey Curie–Weiss law. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Jacobi BG Laitar DS Pu L Wargocki MF DiPasquale AG Fortner KC Schuck SM Brown SN 《Inorganic chemistry》2002,41(18):4815-4823
Trimesityliridium(III) (mesityl = 2,4,6-trimethylphenyl) reacts with O(2) to form oxotrimesityliridium(V), (mes)(3)Ir=O, in a reaction that is cleanly second order in iridium. In contrast to initial reports by Wilkinson, there is no evidence for substantial accumulation of an intermediate in this reaction. The oxo complex (mes)(3)Ir=O oxidizes triphenylphosphine to triphenylphosphine oxide in a second-order reaction with DeltaH++ = 10.04 +/- 0.16 kcal/mol and DeltaS++ = -21.6 +/- 0.5 cal/(mol.K) in 1,2-dichloroethane. Triphenylarsine is also oxidized, though over an order of magnitude more slowly. Ir(mes)(3) binds PPh(3) reversibly (K(assoc) = 84 +/- 3 M(-1) in toluene at 20 degrees C) to form an unsymmetrical, sawhorse-shaped four-coordinate complex, whose temperature-dependent NMR spectra reveal a variety of dynamic processes. Oxygen atom transfer from (mes)(3)Ir=O and dioxygen activation by (mes)(3)Ir can be combined to allow catalytic aerobic oxidations of triphenylphosphine at room temperature and atmospheric pressure with overall activity (approximately 60 turnovers/h) comparable to the fastest reported catalysts. A kinetic model that uses the rates measured for dioxygen activation, atom transfer, and phosphine binding describes the observed catalytic behavior well. Oxotrimesityliridium does not react with sulfides, sulfoxides, alcohols, or alkenes, apparently for kinetic reasons. 相似文献
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投料顺序对动态硫化PP/EPDM性能影响及其机理的研究 总被引:12,自引:0,他引:12
针对PP降解在PP/EPDM动态硫化中对体系产生的不利影响。考察了四种不同投料顺序对PP/EPDM动态硫化物的冲击韧性,加工流动性,交联程度和断面形貌等宏观和微观性能,并进行了不同EPDM含量的动态硫化和非硫化PP/EPDM的性能比较。结果表明,优化投料顺序能实现对动态硫化体系中化学反应对象和化学反应程度的有效干预。 相似文献
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Czechoslovak Mathematical Journal - Let L(n, d) denote the minimum possible number of leaves in a tree of order n and diameter d. Lesniak (1975) gave the lower bound B(n,d) = ⌈2(n −... 相似文献
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Highly dispersed α-Fe_2O_3/NaY,NiO/NaY,and CuO/NaY catalyst systems were pre-pared by impregnation method.Dispersion thresholds of the transition metal oxides on NaY" zeolitewere determined by XRD phase analysis.The dispersion capacities of the transition metal oxides on NaYzeolite are much lower than that estimated on the basis of a closed packed monolayer in the micropores.The catalytic activity and selectivity of the highly dispersed oxide catalyst systems for ethylben-zene and cyclohexane dehydrogenation reactions were reported. 相似文献