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131.
Synthesis of anthracene ethers from anthracene methyl ethers via an acid-catalyzed exchange reaction
Selective synthesis of anthracene ethers was achieved under mild conditions via an acid-catalyzed ether-ether exchange reaction and its scope and limitations, as well as its potential in synthesizing anthracene-based crown ethers, tested. 相似文献
132.
A.?SanthiEmail author U.L.?Kala R.J.?Nedumpara A.?Kurian M.R.P.?Kurup P.?Radhakrishnan V.P.N.?Nampoori 《Applied physics. B, Lasers and optics》2004,79(5):629-633
The fluorescence spectrum of the schiff base obtained from salicylaldehyde and 2-aminophenol is studied using an argon-ion laser as the excitation source and its fluorescence quantum yield (Qf) is determined using a thermal lens method. This is a nondestructive technique that gives the absolute value of Qf without the need for a fluorescence standard. The quantum-yield values are calculated for various concentrations of the solution in chloroform and also for various excitation wavelengths. The value of Qf is relatively high, and is concentration dependent. The maximum value of Qf obtained is nearly 0.78. The high value of the fluorescence quantum yield will render the schiff base useful as a fluorescent marker for biological applications. Photostability and gain studies will assess its suitability as a laser dye. PACS 42.55.Mv; 42.62.Cf; 42.62.Fi; 42.70.Hj 相似文献
133.
Absolute temperature measurement (T < 100 mK region) from anisotropy of gamma radiations emitted from oriented60Co nuclei in a single crystal of hcp cobalt is found to depend on the shape of the crystal. This dependence is attributed to some closure magnetic domains not oriented along thec-axis of the disc shaped crystal studied. A long rectangular strip of cobalt crystal is found to give correct angular distribution ofγ-radiations and, therefore, suitable for thermometry. 相似文献
134.
A.M. Umarji G.V.Subba Rao M.P. Janawadkar T.S. Radhakrishnan 《Journal of Physics and Chemistry of Solids》1980,41(5):421-429
Group IIIa metals and Nb, Hg and Pb containing AxMo6S8 Chevrel phases have been synthesized by low temperature reaction (420–430°C) frorn A metal and Mo6S8. Some of these phases are hitherto unknown. Electrolysis method of preparation of AxMo6S8 reported by Schöllhorn does not yield the desired phases when A = Pb or Ag. Stoichiometry, thermal stability, electrical and superconducting properties of the compounds have been examined. In the PbxMo6S8 system, a series of phases with varying x have been prepared and studied. Group IIIa metal and Nb-compounds are found to be semiconductors with low energies of activation exhibiting p-type behavior in the range 77–300 K. Hg-phase behaves as a metal or a degenerate semiconductor and does not become superconducting above 4.2 K. X-Ray, resistivity and Tc studies show that for x ? 0.8 in PbxMo6S8, the compounds behave more like Mo6S8 and only for x ? 1.0 or (PbBi)1.0, the inherent behavior of the ternary Chevrel phase is exhibited. Seebeck coefficients are small and positive for Mo6S8, Cu and Pb-containing phases in the range 77–300 K. The results are discussed in the light of available band structure of these materials. 相似文献
135.
136.
In neutral thiocyanate medium at low temperatures (0–5°C) cobaltous ion produced an anomalous double wave of nearly equal height. This behaviour was ascribed by earlier workers to a stepwise reduction of cobaltous ion in this medium. A study of the effects of temperature and height of the mercury column as well as the influence of the concentrations of cobalt and thiocyanate on the waves showed that the processes were controlled by chemical reaction and adsorption. It has been concluded that the first wave is a surface kinetic wave resulting from the reduction of [Co(H2O)4(SCN)2] and the second step is a post-adsorption wave brought about by the adsorption of [Co(H2O)5SCN]+ species on the electrode. 相似文献
137.
Remote functionalized zwitterionic diaminodicyanoquinodimethanes are found to exhibit a dramatic enhancement of light emission in the solid state and when doped in polymer films, as compared to the solution state. Crystal structure analysis of prototypical molecules reveals the role of the remote functionality in the solid state molecular organization. Semiempirical quantum chemical computations provide a viable model to explain the interesting phenomenon of fluorescence enhancement as arising from the inhibition of geometry relaxation of the vertical excited state to a nonemitting state. The reversible switching of a doped polymer film fluorescence triggered by solvent vapors is demonstrated. 相似文献
138.
Molecular simulations for simple fluids in narrow slit-shaped carbon pores exhibit crystal-hexatic and hexatic-liquid transitions that are consistent with Kosterlitz-Thouless-Halperin-Nelson-Young theory. The temperature range over which the hexatic phase is stable is dramatically widened under confinement. Remarkably, the transitions, which are continuous for a single adsorbed layer, become weakly first order when the pore can accommodate two molecular layers. Nonlinear dielectric effect measurements for CCl4 and aniline in activated carbon fibers (pore width 1.4 nm) show divergence at these transitions, confirming the hexatic phase. 相似文献
139.
Chemical sensing with microbent optical fiber 总被引:2,自引:0,他引:2
S TL George NA Sureshkumar P Radhakrishnan P Vallabhan CP Nampoori VP 《Optics letters》2001,26(20):1541-1543
We propose and demonstrate the possibility of using a permanently microbent bare optical fiber for detecting chemical species. Two detection schemes, viz., a bright-field detection scheme (for the core modes), and a dark-field detection scheme (for the cladding modes) have been employed to produce a fiber-optic sensor. The sensor described here is sensitive enough to detect concentrations as low as nanomoles per liter of a chemical species, with a dynamic range of more than 6 orders of magnitude. 相似文献
140.
Dr. Sambhu Radhakrishnan Dr. Karl Lauwers Dr. C. Vinod Chandran Dr. Julien Trébosc Dr. Sreeprasanth Pulinthanathu Sree Prof. Johan A. Martens Prof. Francis Taulelle Prof. Christine E. A. Kirschhock Dr. Eric Breynaert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(64):15944-15953
Layered double hydroxides (LDHs) serve a score of applications in catalysis, drug delivery, and environmental remediation. Smarter crystallography, combining X-ray diffraction and NMR spectroscopy revealed how interplay between carbonate and pH determines the LDH structure and Al ordering in ZnAl LDH. Carbonate intercalated ZnAl LDHs were synthesized at different pH (pH 8.5, pH 10.0, pH 12.5) with a Zn/Al ratio of 2, without subsequent hydrothermal treatment to avoid extensive recrystallisation. In ideal configuration, all Al cations should be part of the LDH and be coordinated with 6 Zn atoms, but NMR revealed two different Al local environments were present in all samples in a ratio dependent on synthesis pH. NMR-crystallography, integrating NMR spectroscopy and X-ray diffraction, succeeded to identify them as Al residing in the highly ordered crystalline phase, next to Al in disordered material. With increasing synthesis pH, crystallinity increased, and the side phase fraction decreased. Using 1H−13C, 13C−27Al HETCOR NMR in combination with 27Al MQMAS, 27Al-DQ-SQ measurements and Rietveld refinement on high-resolution PXRD data, the extreme anion exchange selectivity of these LDHs for CO32− over HCO3− was linked to strict Al and CO32−ordering in the crystalline LDH. Even upon equilibration of the LDH in pure NaHCO3 solutions, only CO32− was adsorbed by the LDH. This reveals the structure directing role of bivalent cations such as CO32− during crystallization of [M2+4M3+2(OH)2]2+[A2−]1⋅yH2O LDH phases. 相似文献