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1.
《Tetrahedron》1987,43(15):3523-3532
A detailed study of the regioselectivity of the Fremy's salt oxidation of phenols, including a series of MNDO calculations of the intermediate phenoxy radicals, has been carried out. The analysis of these results has led us to establish a new rule for the para vs. ortho regioselectivity, namely: “C-4 unsubstituted phenols, as well as phenols substituted at C-4 with easy-to-displace groups, undergo oxidation (or oxidative degradation) by the action of Fremy's salt, thus eventually providing the corresponding p-quinones”. A similar rule for the ortho vs. ortho' regioselectivity could not be so precisely formulated since now steric effects play a significant major role.  相似文献   
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综述了近十余年来的一些β-双酮类、苯并咪唑类、苯甲酸类、吡啶类、大环类配体与三价铕(Eu3+)和铽(Tb3+)形成的配合物在液相体系中的荧光性能。其中,重点关注了衡量配合物的荧光性能的最重要的两个标准即量子产率和荧光寿命。文中也总结了在设计和合成优良配体时应该遵循的一些原则:如配体与稀土离子能级要匹配、将溶剂分子排斥出稀土离子配位,最大程度地消除光猝灭因素和无辐射去活化作用而改善光物理性能等,以期得到高的量子产率和长的荧光寿命的稀土配合物。  相似文献   
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A novel fiber-optic sensor structure fabricated by cascading two optical microfiber knot resonators (MKRs) is proposed and demonstrated in this paper. A theoretical model for describing the principle of the sensing structure is given and its temperature responses are characterized experimentally. Experimental results show that high-precision and simultaneous multi-point temperature sensing in micro-scale can be achieved. Such a sensing structure also has the potential for achieving dual-parameter measurement to eliminate the cross-talk between two parameters in micro-scale.  相似文献   
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A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.  相似文献   
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Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy(LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn0.95Cd0.05 O is 3.20. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500℃, the in situ reflection high-energy electron diffraction(RHEED) pattern of Zn Cd O film shows sharp streaky pattern. The maximum Cd content of Zn Cd O film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy(UPS) measurements demonstrate that Zn Cd O film exhibits intense peaks at 4.7 e V and 10.7 e V below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 e V. Above 470 nm, the thin film shows excellent optical transmission.  相似文献   
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The exciton properties of thin nanotube structures are investigated theoretically. Anisotropic size dependencies have been found in the exciton binding energy, the kinetic energy for the relative motions of an electron and a hole, and the wavefunction. These anisotropies arise from the different boundary conditions in the tube-length and circumferential directions, namely, the topological features of nanotubes. We also found that it is possible to change the topology of exciton wavefunctions by varying the tube-length and the tube-radius. These findings suggest that the optical properties of nanotubes such as oscillator strength or nonlinear susceptibilities can be controlled by tuning the structural parameters, thus yielding a novel guiding principle for designing optical functional materials.  相似文献   
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We study the adsorption of the molecular hydrogen on boron-doped polypyrrole ((–C4BH3)n) using first-principles density functional calculations. We find that the binding energy of H2 molecules is slightly reduced to 0.39 eV/H2 from 0.51 eV/H2 as the number of adsorbed H2 molecules increases. This is in sharp contrast to the case of boron-doped fullerenes where the binding energy is drastically reduced as the number of adsorbed H2 molecules increases. We find that the enhancement of H2 adsorption is due to a local charge transfer by H2 adsorption in the B-doped polypyrrole as opposed to a delocalized charge transfer in the B-doped fullerenes. Our finding shows that B-doped carbon systems could be utilized for room temperature hydrogen storage.  相似文献   
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The Pb doped metastable tetragonal ZrO2 (t-ZrO2:Pb) nanoparticles have been successfully synthesized by hydrothermal method. Pb ion doping has great effects on the phases, crystallite sizes and optical band gaps. Systematic structural characterization revealed that the introduction of Pb ion results in lattice expansion. The as-prepared t-ZrO2:Pb with ca 4–6 nm in size has high specific surface area (>150 m2/g) and narrow particle size distributions. The diffuse reflectance spectra investigated that the band gap shifts from ultraviolet (Eg = 5.19 eV) for pure ZrO2 to the visible region for t-ZrO2:Pb and the gap can be effectively adjusted with the content of Pb in nanocrystals. Through thermal treatment, Pb ion doped in ZrO2 crystals was excluded with increasing temperature. At 800 °C, the three t-ZrO2:Pb samples of ZPO-2, ZPO-3 and ZPO-4 still contained the pure tetragonal phase, in which Pb content were not reduced to zero, while the transformation from tetragonal to monoclinic phase occurred due to zero Pb content in ZPO-1. The reason to this transformation and stabilized mechanism of Pb ion in ZrO2 were discussed.  相似文献   
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