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31.
Patrick E. Hartnett Scott M. Dyar Eric A. Margulies Leah E. Shoer Andrew W. Cook Samuel W. Eaton Tobin J. Marks Michael R. Wasielewski 《Chemical science》2015,6(1):402-411
The photophysics of a covalently linked perylenediimide–diketopyrrolopyrrole–perylenediimide acceptor–donor–acceptor molecule (PDI–DPP–PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ∼6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, upon CH2Cl2 vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron–hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ∼4 μs. This result has significant implications for the design of organic solar cells based on covalent donor–acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems. 相似文献
32.
Olankitwanit A Kathirvelu V Rajca S Eaton GR Eaton SS Rajca A 《Chemical communications (Cambridge, England)》2011,47(22):6443-6445
1,3-Alternate calix[4]arene with para-phenylene spacers connecting nitroxide monoradicals and high-spin (S = 1) diradicals provides tetraradical and octaradical scaffolds that possess conformations with slow electron spin relaxation rates (1/T(1)). Such scaffolds may facilitate tuning of relaxation rates that are more favorable for MRI or DNP applications. 相似文献
33.
We present an experimental study of a supersonic nozzle with supersonic iodine injection. This nozzle simulates Chemical Oxygen
Iodine Laser (COIL) flow conditions with non-reacting, cold flows. During the experiments, we used a laser sheet near 565 nm
to excite fluorescence in iodine, which we imaged with an intensified and gated CCD camera. We captured streamwise and semi-spanwise
(oblique-view) images, with fluorescence revealing the material injected into the flow. We identified the flow structures
in the images, and produced quantitative characterizations of the flow morphology and of the mixing between the primary and
injected flow. We considered four injection scenarios. The first scenario includes a single injector positioned downstream
of the nozzle throat. To enhance the mixing between the flows, trip jets are placed in the wake of the single jet. The sonic
trip jets, significantly smaller than the primary supersonic iodine jet, are intended to destabilize the counter-rotating
vortex pair (CRVP) of the primary jet. We compare three different trip jet configurations for their ability to enhance mixing
between the oxygen and iodine flows. 相似文献
34.
Continuous-wave spectra at W-band of four triarylmethyl (trityl) radicals at 100 K in 1∶1 water-glycerol exhibit rhombic electron paramagnetic resonance spectra. The rigid-lattice line widths at W-band are only 3 to 5 times larger than at X-band or S-band, and fluid-solution line widths are much narrower than those for rigid lattice, which indicates that unresolved anisotropic nuclear hyperfine couplings make significant contributions to the rigid-lattice line widths. Spin-flip lines are observed in glassy-solution spectra at X-band and S-band, but not at W-band or 250 MHz. At 100 KT m is dominated by spin diffusion of solvent protons and is independent of microwave frequency. Between about 130 and 170 K, 1/T m for trityl-CH3 is enhanced by rotation of the methyl groups at a rate comparable to inequivalences in the hyperfine interaction. Motional averaging of anisotropic interactions enhances spin echo dephasing between about 200 and 300 K. The temperature dependence of 1/T 1 is similar for the four radicals and is consistent with assignment of the Raman process and a local mode as the dominant relaxation processes. The similarity inT 1 values at W-band and X-band supports this assignment. 相似文献
35.
Gundu H. R. Rao J. M. Gerrard J. W. Eaton J. G. White 《Photochemistry and photobiology》1978,28(4-5):845-850
Abstract— The initial oxygenation or peroxidation of arachidonic acid seems to be an essential step for the synthesis of cyclic endoperoxides and prostaglandins. There has been some evidence and considerable interest in the role of superoxide anion, hydroxyl radicals or singlet oxygen as a source of oxygen in the formation of the active species (free radicals). A test capable of detecting active intermediates of lipid peroxidation and useful for studying the role of free radicals has been developed. The test resulted from the discovery that vitamin E markedly enhanced the reduction of nitroblue tetrazolium (NBT) during arachidonic acid peroxidation. Intact platelets, microsomes, sheep vesicular gland enzymes or peroxidases could provide essential enzyme activity. NBT and vitamin E when added to platelet microsomes inhibited the conversion of 14 C arachidonic acid to HETE, HHT and thromboxanes. The combination also inhibited aggregation of platelets stimulated by collagen, thrombin, ADP and epinephrine. Prolonged incubation with these agents at the highest concentrations used in the study caused no change in morphology and had no deleterious effect on platelet levels of adenine nucleotides and serotonin. Results of our preliminary studies suggest that NBT and vitamin E can detect intermediates of lipid peroxidation, inhibit the conversion of arachidonic acid, prevent platelet aggregation and the release reaction without damaging the platelets morphologically or biochemically. As both the agents are scavengers of free radicals and in combination exert synergistic effects, the test system may serve as a probe in various free radical mediated events and may offer some degree of protection against free radical mediated pathological processes. 相似文献
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