A detailed study of linear and nonlinear optical (NLO) properties obtained by spectroscopy and DFT computations of carbazole-based D-π-A (mono) and A-π-D-π-A (bis) extended styryl dyes is presented. Four different DFT functionals, B3LYP, MO6, BHandHLYP, and CAM-B3LYP are used for computations. The structure–property relationship is examined by correlating bond length alternation/bond order alternation with NLO properties of the dyes. The bis-carbazole styryl dyes possess a higher second-order hyperpolarizability (β) than the mono-carbazole styryl dyes. An increase in the polarity of the environment causes an increase in the first-order hyperpolarizability (βCT or β0) and second-order hyperpolarizability (γ) of the mono- and bis-carbazole styryl compounds. The NLO properties calculated by the CAM-B3LYP and BHandHLYP functionals show good agreement with the spectroscopic results. 相似文献
Replacing conventional reagents with environment friendly reagents is one of the primary goals of modern synthetic methodology and in this very primitive study about utilizing green, naturally available carbohydrate molecules as ligands in transition metal catalyzed reactions, we report Cu/D-glucosamine as an efficient catalyst for aniline synthesis. 相似文献
The aerobic oxidative kinetic resolution of racemic α-hydroxy ketones was accomplished using a chiral Zn-quinine complex as the catalyst in the presence of molecular oxygen. The resulting optimized reaction conditions were applied to resolute different types of racemic α-hydroxy ketones and a maximum of 9.2 selectivity (s) was obtained with 88% ee for the recovered α-hydroxy ketone. 相似文献
The thermal cure kinetics of an epoxidized linseed oil with methyl nadic anhydride as curing agent and 1-methyl imidazole
as catalyst was studied by differential scanning calorimetry (DSC). The curing process was evaluated by non-isothermal DSC
measurements; three iso-conversional methods for kinetic analysis of the original thermo-chemical data were applied to calculate
the changes in apparent activation energy in dependence of conversion during the cross-linking reaction. All three iso-conversional
methods provided consistent activation energy versus time profiles for the complex curing process. The accuracy and predictive
power of the kinetic methods were evaluated by isothermal DSC measurements performed at temperatures above the glass transition
temperature of the completely cured mixture (Tg∞). It was found that the predictions obtained from the iso-conversional method by Vyazovkin yielded the best agreement with
the experimental values. The corresponding activation energy (Ea) regime showed an increase in Ea at the beginning of the curing which was followed by a continuous decrease as the cross-linking proceeded. This decrease
in Ea is explained by a diffusion controlled reaction kinetics which is caused by two phenomena, gelation and vitrification. Gelation
during curing of the epoxidized linseed/methyl nadic anhydride system was characterized by rheological measurements using
a plate/plate rheometer and vitrification of the system was confirmed experimentally by detecting a significant decrease in
complex heat capacity using alternating differential scanning calorimetry (ADSC) measurements. 相似文献
Intumescent material, 2,6,7-trioxa-1-phosphabicyclo-[2,2,2]-octane-4-methanol phosphate (PEPA), is synthesized and characterized using FTIR, 1HNMR and 13CNMR. The degradation properties of PEPA are studied by employing TG and TG?CMS technique. The activation energies for the degradation process of PEPA are calculated by using TG curves obtained from multiple heating rates (Friedman, Kissinger?CAkahira?CSunose and Flynn?CWall?COzawa methods). The degradation that is occurring in the temperature region 307?C366?°C has the highest activation energy. Eventhough the calculated activation energies for the degradation differ depending on the approximation method employed, the trend in variation of activation energy for degradation is similar. Single ion monitoring technique proved the evolution of H2O, CO/C2H4, HCHO, C2H5OH/HCOOH and trace amounts of C2H7O3P and C4H9O4P from the degrading PEPA. The thermal conductivity and stability of the char formed during the TG analysis are also discussed. 相似文献
An unusual dinuclear chiral iron complex has been synthesized and effectively utilized in the asymmetric hydrophosphorylation of aldehydes to synthesize optically active α-hydroxy phosphonates with excellent yield and good enantioselectivity. 相似文献
Highly important trans-3,4-dihydro-2H-1,4-benzoxazine moieties were easily synthesized by domino aziridine ring opening with o-bromophenols and o-chlorophenols followed by the palladium catalyzed coupling-cyclization (intramolecular C(aryl)–N(amide) bond formation) with good to excellent yields. 相似文献
We have investigated the effect of hydrostatic pressure as a function of temperature on the resistivity of a single crystal of the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7). Whereas a strong insulating behaviour is observed at all temperatures at ambient pressure, a clear transition into a metallic-like behaviour is induced when the sample is subjected to a pressure (P) of ~1.0 GPa at T < 70 K. A huge negative piezoresistance ~10(6) in the low temperature region at moderate pressures is observed. When the pressure is increased further (5.5 GPa), the high temperature polaronic state disappears and a metallic behaviour is observed. The insulator to metal transition temperature exponentially increases with pressure and the distinct peak in the resistivity that is observed at 1.0 GPa almost vanishes for P > 7.0 GPa. A modification in the orbital occupation of the e(g) electron between 3d(x(2)-y(2)) and 3d(z(2)-r(2)) states, as proposed earlier, leading to a ferromagnetic double-exchange phenomenon, can qualitatively account for our data. 相似文献
An efficient enantioselective oxidative reaction catalyzed by a chiral cobalt complex has been developed by using molecular oxygen as the stoichiometric oxidant (see scheme). The very mild reaction conditions of the catalytic system provide access to a wide range of benzoins (α‐hydroxyketones) in high yield and excellent enantioselectivity (s (kf/ks) up to 47). This method is very versatile because the sole by‐product of our oxidation process is water, which makes our system more eco‐friendly and green.