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1.
Frequency-resolved femtosecond transient absorption spectra and kinetics measured by optical excitation of the second and first electronic transitions of the (8,3) single-walled carbon nanotube species reveal a unique mutual response between these transitions. Based on the analysis of the spectra, kinetics, and their distinct amplitude dependence on the pump intensity observed at these transitions, we conclude that these observations originate from both the excitonic origin of the spectrum and nonlinear exciton annihilation. 相似文献
2.
V. N. Knyukshto E. I. Zenkevich E. I. Sagun A. M. Shulga S. M. Bachilo 《Journal of fluorescence》2000,10(1):55-68
It was found that mono- and di-meso-phenyl substitution in octaethylporphyrins (OEP)and their chemical dimers with the phenyl ring as a spacer manifests itself in the dramatical shortening of T1 state lifetimes at 295 K (from 1.5 ms down to 2–5 s in degassed toluene solutions). On the other hand, this substitution does not influence spectral-kinetic parameters of S0 and S1 states. The enhancement of the T1 state non-radiative deactivation is explained by torsional librations of the phenyl ring around a single C-C bond in sterically encumbered OEP molecules leading to non-planar dynamic distorted conformations in the excited T1 states. For these compounds with electron-accepting NO2-groups in the meso-phenyl ring the strong non-radiative deactivation of S1 and T1 states (by 2–3 orders of magnitude) is observed upon the displacement of NO2-group from para-to ortho-position of the phenyl ring. The S1 state quenching is caused by the direct intramolecular electron transfer to low-lying CT state of the radical ion pair (the normal region, non-adiabatic case presumably, V = 130–190 cm–1 in dimethylformamide). The additional deactivation of the T1 state is connected with thermally activated transitions to upper-lying CT states as well as the strengthening of intersystem crossing probabilities. 相似文献
3.
S. M. Bachilo T. P. Karkotskaya S. V. Lepeshkevich A. F. Malenchenko B. M. Dzhagarov 《High Energy Chemistry》2000,34(4):251-255
Hemoglobin molecules were studied by stationary and time-resolved laser absorption spectroscopy. On the basis of these results,
the kinetic parameters of oxygenation in the course of methemoglobin formation under the combined action of radiation and
sodium nitrite were analyzed. The kinetics of oxygenation of hemoglobin with an initial methemoglobin concentration of 3%
or lower is described by a two-exponential function. The rate parameters of the reaction are independent of the radiation
history and of the amount of subunits oxidized by sodium nitrite, which is as high as ≈50% relative to the total number of
protein subunits 相似文献
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5.
A. P. Losev S. M. Bachilo D. I. Volkovich Yu. S. Avlasevich K. N. Solov’yov 《Journal of Applied Spectroscopy》1997,64(1):62-71
Photoinduced electron transfer (PET) in a Pd-porphyrin-quinone complex (Pd-P-Q) was investigated using the flash photolysis
method in microsecond and picosecond range and by luminescence. The investigations were performed for toluene solutions. Intramolecular
PETs in the lower excited singlet state (kCT=1.7·1010 sec−1) and in the triplet state (kCT=2.5·108sec−1) were observed. For a quantum yield of the triplet state that is close to 1 in Pd-porphyrin (Pd-P) this yield is equal to
0.4 in Pd-P-Q. This decrease is the result of PET in the excited state and, possibly, in an unrelaxed triplet state. Triplet
Pd-P-Q molecules were efficiently quenched by unexcited molecules, and this process is related to intermolecular charge transfer.
This electron transfer is likely to occur from the Pd-P protion of an excited molecule to the quinone protion of an unexcited
molecule in the collisional complex (Pd-P-Q)2. Charged radicals, formed once the collisional complex is transferred and separated, have a wide absorption band with a maximum
of about 960 nm. The average lifetime of the radicals was about 2 msec.
Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No 1 pp. 61–70, January–February, 1997. 相似文献
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7.
Engel PS Tsvaygboym KP Bachilo S Smith WB Jiang J Chignell CF Motten AG 《The Journal of organic chemistry》2005,70(7):2598-2605
[reaction: see text] Although some aspects of azoxy group radical chemistry have been investigated, unhindered alpha-azoxy radicals remain poorly understood. Here we report the generation of alpha-azoxy radicals under mild conditions by irradiation of alpha-azoxy ketones 4a,b. These compounds undergo alpha-cleavage to yield radicals 5a,b, whose oxygen atom then recombines with benzoyl radicals to produce presumed intermediate 15. Formal Claisen rearrangement gives alpha-benzoyloxyazo compounds 8a,b, which are themselves photolabile, leading to both radical and ionic decomposition. The ESR spectrum of 5a was simulated to extract the isotropic hyperfine splitting constants, which showed its resonance stabilization energy to be exceptionally large. Azoxy compounds have been found for the first time to be good quenchers of triplet excited acetophenone, the main sensitized photoreaction of 7Z in benzene being deoxygenation. While this reaction has been reported previously, it was always in hydrogen atom donating solvents, where chemical sensitization occurred. The principal direct irradiation product of 4bZ and model azoxyalkane 7Z is the E isomer, whose thermal reversion to Z is much faster than that of previously studied analogues. 相似文献
8.
Unusually intense near-infrared (near-IR) photoluminescence has been observed from mixed solutions of C70 and palladium octaethylporphyrin (PdOEP). The novel emission has a spectrum similar to C70 phosphorescence and an intensity that is approximately 20 times greater than that of C70 fluorescence. The emitting species is identified as a noncovalently bound, short-lived triplet exciplex of C70 with PdOEP. The emission is essentially C70 phosphorescence intensified by spin-orbit coupling from the Pd atom in the nearby metalloporphyrin. This supramolecular heavy atom effect increases the C70 emissive quantum yield to approximately 1 x 10(-2) in degassed hexane solution at room temperature. The radiative rate constant is enhanced by a factor of 10(5), to approximately 7 x 10(4) s(-1), which is a value that exceeds the phosphorescence rate constant of PdOEP. Comparative studies in a rigid poly(methyl methacrylate) (PMMA) matrix show that the excited state of the static C70-PdOEP complex decays in approximately 150 ns. A Job's plot analysis shows that the complex has a 1:1 stoichiometry. It forms dynamically in solution and is relatively weakly bound, with an estimated equilibrium constant near 100 M(-1). Qualitatively similar supramolecular heavy atom effects were also observed for complexes of PdOEP with C60 and fullerene derivatives. 相似文献
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10.
A. P. Losev I. N. Nichiporovich S. M. Bachilo G. D. Egorova D. I. Volkovich K. N. Solov'yo 《Journal of Applied Spectroscopy》1995,62(2):311-320
Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, Minsk, 220072, 70, F. Skorina Ave., Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 2, pp. 152–163, March–April, 1995. 相似文献