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51.
In this paper, based on the theory of variable exponent spaces, we study the higher integrability for a class of nonlinear elliptic equations with variable growth and discontinuous coefficients. Under suitable assumptions, we obtain a local gradient estimate in Orlicz space for weak solution. 相似文献
52.
Dr. Zafar Mahmood Noreen Rehmat Prof. Shaomin Ji Prof. Jianzhang Zhao Shanshan Sun Dr. Mariangela Di Donato Prof. Mingde Li Maria Teddei Prof. Yanping Huo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14912-14918
Zinc(II) bis(dipyrrin) complexes, which feature intense visible absorption and efficient symmetry breaking charge transfer (SBCT) are outstanding candidates for photovoltaics but their short lived triplet states limit applications in several areas. Herein we demonstrate that triplet excited state dynamics of bis(dipyrrin) complexes can be efficiently tuned by attaching electron donating aryl moieties at the 5,5′-position of the complexes. For the first time, a long lived triplet excited state (τT=296 μs) along with efficient ISC ability (ΦΔ=71 %) was observed for zinc(II) bis(dipyrrin) complexes, formed via SBCT. The results revealed that molecular geometry and energy gap between the charge transfer (CT) state and triplet energy levels strongly control the triplet excited state properties of the complexes. An efficient triplet–triplet annihilation upconversion system was devised for the first time using a SBCT architecture as triplet photosensitizer, reaching a high upconversion quantum yield of 6.2 %. Our findings provide a blueprint for the development of triplet photosensitizers based on earth abundant metal complexes with long lived triplet state for revolutionary photochemical applications. 相似文献
53.
Six mono/double‐layered 2D and three 3D coordination polymers were synthesized by a self‐assembly reaction of Zn (II) salts, organic dicarboxylic acids and L1/L2 ligands. These polymeric formulas are named as [Zn(L1)(C4H2O4)0.5 (H2O)]n·0.5n(C4H2O4)·2nH2O ( 1 ), [Zn2(L2)(C4H2O4)2]n·2nH2O ( 2 ), [Zn(L1)(m‐BDC)]n ( 3 ), [Zn2(L2)(m‐BDC)2]n·2nH2O ( 4 ), [Zn3(L1)2(p‐BDC)3(H2O)4]n·2nH2O ( 5 ), [Zn2(OH)(L2) (p‐BDC)1.5]n ( 6 ), [Zn2(L1)(p‐BDC)2]n·5nH2O ( 7 ), [Zn2(L2)(p‐BDC)2]n·3nH2O ( 8 ) and [Zn2(L1)(C4H4O4)1.5(H2O)]n·n(ClO4)·nH2O ( 9 ) [L1 = N,N′‐bis (pyridin‐4‐ylmethyl)propane‐1,2‐diamine, L2 = N,N′‐bis (pyridin‐3‐ylmethyl)propane‐1,2‐ diamine, m‐BDC2? = m‐benzene dicarboxylate, p‐BDC2? = p‐benzene dicarboxylate]. Meanwhile, these polymers have been characterized by elemental analysis, infrared, thermogravimetry (TG), photoluminescence, powder and single‐crystal X‐ray diffraction. Polymers 1–6 present mono‐ and double (4,4)‐layer motifs accomplished by L1/L2 ligands with diverse conformations and organic dicarboxylates, and the layer thickness locates in the range of 5.8–15.0 Å. In three 3D polymers, the L1 and L2 molecules adopt the same cis‐conformations and join adjacent Zn (II) cations together with p‐BDC2? or succinate, giving rise to different binodal (4,4)‐c nets with (4.52.83)(4.53.72) ( 7 ), pts ( 8 ) topology and twofold interpenetrated binodal (5,5)‐c nets with (32.44.52.62)(3.43.52.64) ( 9 ). Therefore, the diverse conformations of the two bis (pyridyl)‐propane‐1,2‐diamines and the feature of different organic dicarboxylate can effectively influence the architectures of these polymers. Powder X‐ray diffraction patterns demonstrate that these bulk solid polymers are pure phase. TG analyses indicate that these polymers have certain thermal stability. Luminescent investigation reveals that the emission maximum of these polymers varies from 402 to 449 nm in the solid state at room temperature. Moreover, 1 , 3 and 5–8 show average luminescence lifetimes from 8.81 to 16.30 ns. 相似文献
54.
Dr. Subrat Kumar Barik Shou-Chih Huo Chun-Yen Wu Tzu-Hao Chiu Jian-Hong Liao Dr. Xiaoping Wang Dr. Samia Kahlal Prof. Jean-Yves Saillard Prof. C. W. Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(46):10471-10479
Although atomically precise polyhydrido copper nanoclusters are of prime interest for a variety of applications, they have so far remained scarce. Herein, this work describes the synthesis of a dithiophosphate-protected copper(I) hydride-rich nanocluster (NC), [Cu30H18{S2P(OnPr)2}12] ( 1H ), fully characterized by various spectroscopic methods and single-crystal X-ray diffraction. The X-ray structure of 1H reveals an unprecedented central Cu12 hollow icosahedron. Six faces of this icosahedron are capped by Cu3 triangles, the whole Cu30 core being wrapped by twelve dithiophosphate ligands and the whole cluster has ideal S6 symmetry. The locations of the 18 hydrides in 1H were ascertained by a single-crystal neutron diffraction study. They are composed of three types: capping μ3-H, interstitial μ4-H (seesaw) and μ5-H ligands (square pyramidal), in good agreement with the DFT simulations. The numbers of hydrides and ligand resonances in the 1H NMR spectrum of 1H are in line with their coordination environment in the solid state, retaining the S6 symmetry in solution. Furthermore, two new Se-protected polyhydrido copper nanoclusters, [Cu30H18{Se2P(OR)2}12] ( 2H : R=iPr 3H : R=iBu) were synthesized from their sulfur relative 1H via ligand displacement reaction and their X-ray structures feature the exceptional case where both the NC shape and size are fully conserved during the course of ligand exchange. DFT and TD-DFT calculations allow understanding the bonding and optical properties of clusters 1H – 3H . In addition, the reaction of 1H with [Pd(PPh3)2Cl2] in the presence of terminal alkynes led to the formation of new bimetallic Cu−Pd alloy clusters [PdCu14H2{S2P(OnPr)2}6(C≡CR)6] ( 4 : R=Ph; 5 : R = C6H4F). 相似文献
55.
Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions
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Xiaodong Shen Haohua Huo Chuanyong Wang Bo Zhang Dr. Klaus Harms Prof. Dr. Eric Meggers 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9720-9726
Octahedral iridium(III) complexes containing two bidentate cyclometalating 5‐tert‐butyl‐2‐phenylbenzoxazole ( IrO ) or 5‐tert‐butyl‐2‐phenylbenzothiazole ( IrS ) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5–5.0 mol % catalyst loading) for a variety of reactions with α,β‐unsaturated carbonyl compounds, namely Friedel–Crafts alkylations (94–99 % ee), Michael additions with CH‐acidic compounds (81–97 % ee), and a variety of cycloadditions (92–99 % ee with high d.r.). Mechanistic investigations and crystal structures of an iridium‐coordinated substrates and iridium‐coordinated products are consistent with a mechanistic picture in which the α,β‐unsaturated carbonyl compounds are activated by two‐point binding (bidentate coordination) to the chiral Lewis acid. 相似文献
56.
Cong-De Huo Xia-Zhen Bao Dong-Cheng Hu Xiao-Dong Jia Chou-Gu Sun Cheng Wang 《中国化学快报》2014,25(5):699-701
A solid complex,readily prepared from commercially available sodium triphenylphosphine-m-sulfonate(TPPMS) and carbon tetrabromide,can be used as an easily recoverable and reusable catalyst system for one-pot condensation of 2-naphthol with aldehydes to construct 14-aryl(alkyl)-14H-dibenzo[a j]-xanthene derivatives and one-pot condensation of 2-naphthol with aldehydes and cyclic 1 3-dicarbonyl compounds to construct 12-aryl(alkyl)-8 9 10 12-tetrahydrobenzo[a]xanthen-11-one derivatives. 相似文献
57.
58.
The insertion of an alkyne into transition metal–hydrogen bonds is a key elementary step in catalytic polymerization and hydrogenation processes. It was found that a (Z)- or (E)-type alkyenyl complex can be formed through trans/cis stereospecific processes. In this work, the reaction mechanism of Cp2M(L)H [Cp = η5-C5H5; M = Nb, V; L = CO, P (OMe)3] with dimethylacetylene dicarboxylate (DMAD), and the factors influencing the stereoselectivity have been investigated based on density functional theory calculations. The calculated results show that all of the reactions are exothermic. For L = CO, the Z-isomer product forms first even at low temperatures because of the low Gibbs free energy barrier (ΔG#). Then the Z-pro converts to E-pro , while for L = P (OMe)3, the exclusive product is the E-isomer. For different metal centers, the reaction mechanisms of the Cp2M(CO)H + DMAD (M = Nb and V) reaction are similar, while their products are different at room temperature. For M = Nb, because the energy barrier of the isomerization from Z-pro to E-pro is low and the relative free energies of Z-pro and E-pro are almost equal, both Z-pro and E-pro can be obtained. While for the Cp2V(CO)H + DMAD reaction, only the Z-pro can be obtained under mild conditions, E-pro can be obtained only at high temperatures. For the Cp2M(CO)H+DMAD(M=V and Nb) reactions, the formation of E-isomer products proceeds via two five-membered ring transition states. The calculated results provide an reasonable explanation for the experimental results and predict a new insertion reaction. 相似文献
59.
Microstructural evolution and grain refinement mechanism in AZ31 magnesium alloy subjected to sliding friction treatment were investigated by means of transmission electron microscopy. The process of grain refinement was found to involve the following stages: (I) coarse grains were divided into fine twin plates through mechanical twinning; then the twin plates were transformed to lamellae with the accumulation of residual dislocations at the twin boundaries; (II) the lamellae were separated into subgrains with increasing grain boundary misorientation and evolution of high angle boundaries into random boundaries by continuous dynamic recrystallisation (cDRX); (III) the formation of nanograins. The mechanisms for the final stage, the formation of nanograins, can be classified into three types: (i) cDRX; (ii) discontinuous dynamic recrystallisation (dDRX); (iii) a combined mechanism of prior shear-band and subsequent dDRX. Stored strain energy plays an important role in determining deformation mechanisms during plastic deformation. 相似文献
60.
Xin Xiao Shangjin He Meihan Dan Yang Su Fei Huo Wangqing Zhang 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3177-3190
Dispersion RAFT polymerization of styrene in the alcohol/water mixture mediated with the brush macro‐RAFT agent of poly[poly(ethylene oxide) methyl ether vinylphenyl‐co‐styrene] trithiocarbonate [P(mPEGV‐co‐St)‐TTC] with similar molecular weight but different chemical composition is investigated. Well‐controlled RAFT polymerization including an initial slow homogeneous polymerization and a subsequent fast heterogeneous polymerization at almost complete monomer conversion is achieved. The molecular weight of the synthesized block copolymer increases linearly with the monomer conversion, and the polydispersity is relatively narrow (PDI < 1.3). The RAFT polymerization kinetics is dependent on the chemical composition in the brush macro‐RAFT agents, and those with high content of hydrophobic segment lead to fast RAFT polymerization. The growth of the block copolymer nano‐objects during the RAFT polymerization is explored, and various block copolymer nano‐objects such as nanospheres, worms, vesicles and large‐compound‐micelle‐like particles are prepared. The parameters such as the chemical composition in the brush macro‐RAFT agent, the chain length of the solvatophobic block, the concentration of the feeding monomer and the solvent character affecting the size and morphology of the block copolymer nano‐objects are investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3177–3190 相似文献