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1.
Probing the donor-acceptor proximity on the physicochemical properties of porphyrin-fullerene dyads: "tail-on" and "tail-off" binding approach. 总被引:1,自引:0,他引:1
F D'Souza G R Deviprasad M E El-Khouly M Fujitsuka O Ito 《Journal of the American Chemical Society》2001,123(22):5277-5284
A new approach of probing proximity effects in porphyrin-fullerene dyads by using an axial ligand coordination controlled "tail-on" and "tail-off" binding mechanism is reported. In the newly synthesized porphyrin-fullerene dyads for this purpose, the donor-acceptor proximity is controlled either by temperature variation or by an axial ligand replacement method. In o-dichlorobenzene, 0.1 M (TBA)ClO(4), the synthesized zincporphyrin-fullerene dyads exhibit seven one-electron reversible redox reactions within the accessible potential window of the solvent and the measured electrochemical redox potentials and UV-visible absorption spectra reveal little or no ground-state interactions between the C(60) spheroid and porphyrin pi-system. The proximity effects on the photoinduced charge separation and charge recombination are probed by both steady-state and time-resolved fluorescence techniques. It is observed that in the "tail-off" form the charge-separation efficiency changes to some extent in comparison with the results obtained for the "tail-on" form, suggesting the presence of some through-space interactions between the singlet excited zinc porphyrin and the C(60) moiety in the "tail-off" form. The charge separation rates and efficiencies are evaluated from the fluorescence lifetime studies. The charge separation via the singlet excited states of zinc porphyrin in the studied dyads is also confirmed by the quick rise-decay of the anion radical of the C(60) moiety within 20 ns. Furthermore, a long-lived ion pair with lifetime of about 1000 ns is also observed in the investigated zinc porphyrin-C(60) dyads. 相似文献
2.
S. H. El-Khouly 《Journal of Radioanalytical and Nuclear Chemistry》2006,270(2):391-398
Summary Amorphous zirconium tungstate inorganic ion-exchanger has been prepared under optimum conditions and characterized by IR,
X-ray and thermal analysis. Surface area and capacity are determined. It has characteristic IR absorption peaks at 3242, 1628,
955, 868 and 432 cm-1 and is thermally stable up to 450 °C. Its surface area was 16 m2/g with an exchange capacity of 0.541 meq/g. The sorption of radioactive europium from different media at ambient temperature
by the zirconium tungstate (ZW) exchanger has been studied. The aim was to optimize the conditions for sorbing Eu from radioactive
waste and cleaned the ZW from for recycling. The effect of contact time, metal concentration, pH and temperature has been
measured. Percentual uptake of Eu(III) reaches 95% for HCl at pH 4 and increases with temperature indicating an endothermic
sorption process. Uptake of Zn(II) and Co(II) on ZW from acetic acid was found to be 42% and 24% for cobalt and zinc, respectively.
Desorption after saturation and the effect of other radioactive ions on the percentual uptake of Eu on ZW were investigated.
A solution of 3M HCl releases 90%, 25% and 13% of the loaded Eu(III), Co(II) and Zn(II), respectively. 相似文献
3.
A. A. El-Khouly M. A. H. Hafez I. M. M. Kenawy 《Russian Journal of Electrochemistry》2006,42(3):225-232
Some kinetic and activation thermodynamic functions for the electrodeposition of palladium, thallium, and tellurium from the
best selected baths, viz. niclosamide bath [5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide] for Pd, alizarin red bath
for Tl, and salicylaldehyde bath for Te, are determined. Reaction rate constant (k), half-lifetime (t
1/2), activation energy (E
a), and such activation thermodynamic parameters as entropy change (ΔS*), enthalpy change (ΔH*), and Gibbs free energy (ΔG*) are calculated by applying the rate theory of the first-order reaction and the Eyring theory of the reaction rate. The
effect of temperature change in the range of 30–60°C on the above parameters is studied and thoroughly discussed. The effect
of metal type on both the reaction rate and the activation energy is also investigated.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 3, pp. 264–271.
The text was submitted by the authors in English. 相似文献
4.
Bulk superconducting samples of type Tl0.5Pb0.5Sr1.6Ba0.4CaCu2−x
Ru
x
O7−δ, (Tl, Pb)/Sr-1212, with 0.0 ≤ x ≤ 0.525 were prepared by the conventional one-step solid-state reaction technique. The prepared samples were investigated
using X-ray powder diffraction, electrical resistivity and electron paramagnetic resonance (EPR) measurements. Enhancement
of the phase formation, superconducting transition temperature T
c and hole carriers concentration P was observed up to x = 0.075. For x > 0.075, a reverse trend was observed. EPR spectra were measured at different temperatures (120–290 K) for all prepared samples.
The number of spins N participating in the resonance and the paramagnetic susceptibility χ were calculated as a function of both Ru-content and
temperature. N and χ increased as the Ru-content increased. A linear relationship between logN and 1/T was established, from which the activation energy E
a was calculated as a function of the Ru-content. The temperature dependence of χ was fitted according to Curie–Weiss type
of magnetic behavior. Curie constant C, Curie temperature θ, the effective magnetic moment μ and the electronic specific heat γ were estimated as a function of the Ru-content. 相似文献
5.
ABSTRACTBayfol (PC-PBT blend ?lm) is a class of polymeric solid-state nuclear track detector which has a lot of applications in several radiation detection ?elds. It is a bisphenol-A polycarbonate PC blended with polybutylene terephthalate PBT. Bayfol/Palladium (PC-PBT/Pd) nanocomposite films have been deposited using the molding technique. It is worth mentioning that this report is almost the first one dealing with the topic of the changes of physical properties of Bayfol/Pd nanocomposite due to laser exposure. Samples from PC-PBT/Pd (5?wt%) nanocomposite were exposed to IR-pulsed laser of 5-W power, capable of producing 2000 pulses per second with pulse duration of 200?ns at 904?nm. The laser fluences were in the range 2–25?J/cm2. The resultant modi?cations in the exposed nanocomposite samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction (XRD), UV spectroscopy and color difference studies. The results indicate the proper dispersion of Pd nanoparticles in the PC-PBT matrix that causes a strong intermolecular interaction between Pd and PC-PBT, resulted in an increase in refractive index and the amorphous phase. Also, it is found that the laser exposure reduces the optical energy gap that could be attributed to the increase in structural disorder of the exposed PC-PBT/Pd nanocomposites due to crosslinking. Further, the color intensity ΔE, which is the color difference between the exposed samples and the non-exposed one, was increased with increasing the laser fluence, convoyed by a significant increase in the green and yellow color components. 相似文献
6.
7.
El-Khouly ME Shim SH Araki Y Ito O Kay KY 《The journal of physical chemistry. B》2008,112(13):3910-3917
Photoinduced intramolecular electron-transfer events of the newly synthesized subphthalocyanine-triphenylamine-fullerene triad (SubPc-TPA-C60) and subphthalocyanine-triphenylamine-bisfullerene tetrad (SubPc-TPA-(C(60))(2)) were studied. The geometric and electronic structures of the triad were probed by ab initio B3LYP/3-21G method, which predicts SubPc-TPA(*+)-C(60)(*-) as a stable charge-separated state. The photoinduced events via the excited singlet state of SubPc were monitored by time-resolved emission measurements as well as transient absorption techniques. Efficient charge-separations via the excited states of SubPc were observed with the rates of approximately 10(10) s(-)1. Compared with the SubPc-TPA dyad, a long-lived charge-separated state was observed for the SubPc-TPA-C(60) triad with the lifetime of the radical ion pairs (tau(RIP)) of 670 ns in benzonitrile. Interestingly, further charge stabilization was achieved in the charge-separated state of SubPc-TPA-(C(60))(2), in which the tau(RIP) was found to be 1050 ns in benzonitrile. 相似文献
8.
El-Khouly ME Anandakathir R Ito O Chiang LY 《The journal of physical chemistry. A》2007,111(30):6938-6944
Construction of starburst C60(>DPAF-C9)4 pentads was coupled with the use of highly fluorescent diphenylaminofluorene-C9 (DPAF-C9) addends as donor components in conjunction with the fullerene acceptor during single-photon excitation processes. High quantum yields (PhiCS) of charge-separation processes in the range 0.83-0.90 for C60(>DPAF-C9)n (n = 1, 2, or 4) were obtained in the formation of C60*-(>DPAF*+-C9)(>DPAF-C9)n-1 transient states. The lifetime of the radical ion-pairs (tauRIP) was found to be 900 ns for starburst C60(>DPAF-C9)4 (3) samples, which is 6-fold longer than that of the linear analogue C60(>DPAF-C9) (1), with a ca. 2 times increase of the charge-separation rate (kCS) compared to that of 1. These data implied the important role of sterically hindered DPAF-C9 pendants arranged in a starburst-like environment that encapsulates the central C60 core on extending the tauRIP. We interpreted the phenomena by the occurrence of intramolecular migration or exchange of electron or positive charge among multiple DPAF-C9 pendants of C60*-(>DPAF*+-C9)(>DPAF-C9)n-1, which gives an increased rate in charge generation and delayed charge recombination. 相似文献
9.
El-Khouly ME Kang ES Kay KY Choi CS Aaraki Y Ito O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(10):2854-2863
Silicon-phthalocyanine-cored fullerodendrimers with up to eight fullerene substituents (SiPc-n C(60); n=2, 4, and 8) have been synthesized. Photophysical properties of newly synthesized SiPc-n C(60) have been investigated by time-resolved fluorescence and transient absorption analysis with pulsed laser light. Laser photolysis measurements suggest the occurrence of a charge-separation process from (1)SiPc* to the C(60) subunits. The nanosecond transient absorption spectra in the near-IR region indicate that the lifetimes of the formed radical ion pairs are prolonged on the order of SiPc-8 C(60)>SiPc-4 C(60)>SiPc-2 C(60), which may be related to the electron migration among the C(60) subunits. The usefulness of SiPc-n C(60) as light-harvesting systems, evaluated as a ratio of the rates of charge recombination to those of charge separation, increases markedly with the dendrimer generation. 相似文献
10.