排序方式: 共有35条查询结果,搜索用时 171 毫秒
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G. H. Gelinck J. M. Warman H. F. M. Schoo 《Journal of Radioanalytical and Nuclear Chemistry》1998,232(1-2):115-120
Using the pulse-radiolysis time-resolved microwave conductivity technique the mobility and decay kinetics of radiation-induced
charge carriers is studied in a series of poly(2,5-dialkoxy-phenylene vinylene) derivatives. The lower limit to the sum of
the mobilities of the positive and negative charge carriers, Σμmin, depends strongly on the alkoxy functionalization and ranges from 1.2·10−7 to 1.4·10−6 m2/V·s at room temperature. Σμmin increases with the degree of order in the material. The after-pulse conductivity decay kinetics are disperse and are controlled
by a combination of charge recombination and trapping. 相似文献
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A large microwave conductivity change is observed on laser flash photolysis (308 nm) of a solution of TMPD in CCl4. This is ascribed to single-photon ionisation of the solute resulting in the formation of a stable TMPD+Cl? ion pair. The dipole moment of the ion pair is estimated to be (8.7 ± 0.9)(φ*)? where φ* is the quantum efficiency for ion-pair formation. 相似文献
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David A. Armstrong Eric.S. Sennhauser John M. Warman Ulrich Sowada 《Chemical physics letters》1982,86(3):281-284
The rate coefficient for electron—ion recombination at 292 K rises to a value of 7 x 10?5 cm3 s?1 in CO2 at 13 x 1019 molecule cm?3, but is non-linear with density above 8 x 1019 molecule cm?3. In ammonia it passes through a definite maximum of 7 x 10?5 cm3 s?1 at 2.4 x 1019 molecule cm?3 相似文献
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J J Piet W Schuddeboom B R Wegewijs F C Grozema J M Warman 《Journal of the American Chemical Society》2001,123(22):5337-5347
The flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to investigate the nature of the relaxed S(1) state of 9,9'-bianthryl (AA), 10-cyano-9,9'-bianthryl (CAA), and 10,10'-dicyano-9,9'-bianthryl (CAAC). Changes in both the real, Deltaepsilon' (dielectric constant), and imaginary, Deltaepsilon' ' (dielectric loss), components of the complex permittivity have been measured. The dielectric loss transients conclusively demonstrate the dipolar nature of S(1) for all three compounds in the pseudopolar solvents benzene and 1,4-dioxane, and even in the nonpolar solvents n-hexane and cyclohexane. The required symmetry breaking is considered to result from density and structural fluctuations in the solvent environment. The dipole relaxation times for AA (CAAC) are ca. 2 ps for the alkanes and 7.9 (5.3) and 14 (14) ps for benzene and dioxane, respectively. The time scale of dipole relaxation for the symmetrical compounds is much shorter than that for rotational diffusion and is attributed to intramolecular, flip-flop dipole reversal via a neutral excitonic state. The dipole moment of the transient dipolar state is estimated to be ca. 8 D, that is much lower than the value of ca. 20 D determined from the solvatochromic shifts in the fluorescence in intermediate to highly polar solvents which corresponds to close to complete charge separation. For the asymmetric compound, CAA, a dipole moment close to 20 D is found in all solvents, including n-hexane. Dipole relaxation in this case occurs on a time scale of several hundred picoseconds and is controlled mainly by diffusional rotation of the molecules. The mechanism and kinetics of formation of the dipolar excited states are discussed in the light of these results. 相似文献
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van Delden RA Huck NP Piet JJ Warman JM Meskers SC Dekkers HP Feringa BL 《Journal of the American Chemical Society》2003,125(50):15659-15665
The photochemical control of ground- and excited-state chirality of (M)-cis-(1) and (P)-trans-(2)-2-nitro-7-(dimethylamino)-9-(2',3'-dihydro-1'H-naphtho[2,1-b]-thiopyran-1'-ylidene)-9H-thioxanthene is described. It is shown that while ground state chirality can be controlled photochemically by irradiation with light of different wavelengths, the excited state chirality can be tuned either photochemically in a similar way or by appropriate choice of solvent. In benzene solution, circularly polarized luminescence of the two isomers with opposite ground-state helicity, (M)-cis-1 and (P)-trans-2, revealed corresponding excited states of opposite helicity. On the contrary, in n-hexane solution, circularly polarized luminescence was identical for the two forms indicating identical excited state chirality. Circularly polarized luminescence (CPL), steady-state and time-dependent fluorescence, and time-resolved microwave conductivity (TRMC) measurements in both n-hexane and benzene are reported, which provide an explanation for the remarkable solvent dependence of excited-state chirality. 相似文献