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961.
An Unexpected Fluctuating Reactivity for Odd and Even Carbon Numbers in the TiO2‐Based Photocatalytic Decarboxylation of C2‐C6 Dicarboxylic Acids
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Yiran Sun Dr. Wei Chang Dr. Hongwei Ji Dr. Chuncheng Chen Prof. Wanhong Ma Prof. Jincai Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(7):1861-1870
The degradation behaviours of five straight‐chain dicarboxylic acids (from ethanedioic acid to hexanedioic acid) were compared in aqueous TiO2‐based photocatalysis. When all other conditions were identical, the degradation rates were found to fluctuate regularly with the parity of the number of carbon atoms. Dicarboxylic acids with an even number of carbon atoms (e‐DAs) always degraded more slowly than those acids with an odd number of carbon atoms (o‐DAs). This unusual fluctuation in the reactivity for the degradation of dicarboxylic acids by TiO2‐based photocatalysis is very closely related to the different pre‐coordination modes of the acids with the photocatalyst. Attenuated total reflection FTIR (ATR‐FTIR) of e‐DAs labelled with 13C showed that both carboxyl groups of the acid coordinate to TiO2 through bidentate chelating forms. In contrast, only one carboxyl group of the o‐DAs coordinated to TiO2 in a bidentate chelating manner, whereas the other formed a monodentate binding linkage. The bidentate chelating form with bilateral symmetric coordination did not favour degradation. Isotope‐labelling experiments were performed with 18O2 to observe the different ways in which incorporated oxygen entered the initial decarboxylated products of e‐ and o‐DAs. For the degradation of butanedioic acid, (45.9±0.5) % of the oxygen in the formed propanedioic acid came from H2O, whereas for pentanedioic acid, (97.4±0.2) % of the oxygen in the formed butanedioic acid came from H2O. Our results demonstrate that in TiO2‐based photocatalysis, the reactivity of active species, such as . OH/hvb+, is far from non‐selective and that the attacks of these active species on organic substrates are significantly affected by the coordination patterns of the substrates on the TiO2 surface. 相似文献
962.
Highly Luminescent N‐Doped Carbon Quantum Dots as an Effective Multifunctional Fluorescence Sensing Platform
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Dr. Zhaosheng Qian Juanjuan Ma Xiaoyue Shan Dr. Hui Feng Prof. Linxiang Shao Prof. Jianrong Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(8):2254-2263
The doping of carbon quantum dots with nitrogen provides a promising direction to improve fluorescence performance and broaden their applications in sensing systems. Herein we report a one‐pot solvothermal synthesis of N‐doped carbon quantum dots (NCQDs) and the synthesis of a series of NCQDs with different nitrogen contents. The as‐prepared NCQDs were compared with carbon quantum dots (CQDs); the introduction of nitrogen atoms largely increased the quantum yield of NCQDs and highest emission efficiency is up to 36.3 %. The fluorescence enhancement may originate from more polyaromatic structures induced by incorporated nitrogen atoms and protonation of nitrogen atoms on dots. It was found that NCQDs can act as a multifunctional fluorescence sensing platform because they can be used to detect pH values, AgI, and FeIII in aqueous solution. The fluorescence intensity of NCQDs is inversely proportional to pH values across a broad range from 5.0 to 13.5, which indicates that NCQDs can be devised as an effective pH indicator. Selective detection of AgI and FeIII was achieved based on their distinctive fluorescence influence because AgI can significantly enhance the fluorescence whereas FeIII can greatly quench the fluorescence. The quantitative determination of AgI can be accomplished with NCQDs by using the linear relationship between fluorescence intensity of NCQDs and concentration of AgI. The sensitive detection of H2O2 was developed by taking advantage of the distinct quenching ability of FeIII and FeII toward the fluorescence of NCQDs. Cellular toxicity test showed NCQDs still retain low toxicity to cells despite the introduction of a great deal of nitrogen atoms. Moreover, bioimaging experiments demonstrated that NCQDs have stronger resistance to photobleaching than CQDs and more excellent fluorescence labeling performance. 相似文献
963.
María José Heras‐Ojea Daniel Reta Mañeru Lidia Rosado Dr. Juan Rubio Zuazo Dr. German R. Castro Subrata Tewary Dr. Gopalan Rajaraman Dr. Guillem Aromí Dr. Erika Jiménez Dr. E. Carolina Sañudo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(33):10439-10445
The new diimine fluorescent ligand ACRI‐1 based on a central acridine yellow core is reported along with its coordination complex [Co2( ACRI‐1 )2] ( 1 ), a fluorescent weak ferromagnet. Due to the strong fluorescence of the acridine yellow fluorophore, it is not completely quenched when the ligand is coordinated to CoII. The magnetic properties of bulk complex 1 and its stability in solution have been studied. Complex 1 has been deposited on highly ordered pyrolitic graphite (HOGP) from solution. The thin films prepared have been characterized by AFM, time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS), grazing incidence X‐ray diffraction (GIXRD), X‐ray absorption spectroscopy (XAS), X‐ray magnetic circular dichroism (XMCD) and theoretical calculations. The data show that the complex is robust and remains intact on the surface of graphite. 相似文献
964.
Rationally Investigating the Influence of T1 Location on Electroluminescence Performance of Aryl Amine Modified Phosphine Oxide Materials
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Chunmiao Han Liping Zhu Jing Li Fangchao Zhao Dr. Hui Xu Prof. Dongge Ma Prof. Pengfei Yan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16350-16359
The correspondence between triplet location effect and host‐localized triplet–triplet annihilation and triplet–polaron quenching effects was performed on the basis of a series of naphthyldiphenylamine (DPNA)‐modified phosphine oxide hosts. The number and ratio of DPNA and diphenylphosphine oxide was adjusted to afford symmetrical and unsymmetrical molecular structures and different electronic environments. As designed, the first triplet (T1) states were successfully localized on the specific DPNA chromophores. Owing to the meso‐ and multi‐insulating linkages, identical optical properties and comparable electrical performance was observed, including the same first singlet (S1) and T1 energy levels to support the similar singlet and triplet energy transfer and the close frontier molecular orbital energy levels. This established the basis of rational investigation on T1 location effect without interference from other optoelectronic factors. 相似文献
965.
Oligosiloxane Functionalized with Pendant (1,3‐Bis(9‐carbazolyl)benzene) (mCP) for Solution‐Processed Organic Electronics
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Dr. Dianming Sun Dr. Zhaomin Yang Dr. Zhongjie Ren Dr. Huihui Li Prof. Martin R. Bryce Prof. Dongge Ma Prof. Shouke Yan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16233-16241
A new oligosiloxane derivative (ODCzMSi) functionalized with the well‐known 1,3‐bis(9‐carbazolyl)benzene (mCP) pendant moiety, directly linked to the silicon atom of the oligosiloxane backbone, has been synthesized and characterized. Compared to mCP, the attachment of the oligosiloxane chain significantly improves the thermal and morphological stabilities with a high decomposition temperature (Td=540 °C) and glass transition temperature (Tg=142 °C). The silicon–oxygen linkage of ODCzMSi disrupts the backbone conjugation and maintains a high triplet energy level (ET=3.0 eV). A phosphorescent organic light‐emitting diode (PhOLED) using iridium bis(4,6‐difluorophenyl)pyridinato‐N,C2 picolinate (FIrpic) as the emitter and ODCzMSi as the host shows a relatively low turn‐on voltage of 5.0 V for solution‐processed PhOLEDs, maximum external quantum efficiency of 9.2 %, and maximum current efficiency of 17.7 cd A?1. The overall performance of this device is competitive with the best reported solution‐processed blue PhOLEDs. Memory devices using ODCzMSi as an active layer exhibit non‐volatile write‐once read‐many‐times (WORM) characteristics with high stability in retention time up to 104 s and a low switch on voltage. This switching behaviour is explained by different stable conformations of ODCzMSi with high or low conductivity states which are obtained under the action of electric field through a π–π stacking alignment of the pendant aromatic groups. These results with both PhOLEDs and memory devices demonstrate that this oligosiloxane–mCP hybrid structure is promising and versatile for high performance solution‐processed optoelectronic applications. 相似文献
966.
Reactivity of Oxygen Radical Anions Bound to Scandia Nanoparticles in the Gas Phase: CH Bond Activation
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Li‐Hua Tian Jing‐Heng Meng Dr. Xiao‐Nan Wu Dr. Yan‐Xia Zhao Dr. Xun‐Lei Ding Prof. Dr. Sheng‐Gui He Dr. Tong‐Mei Ma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):1167-1175
The activation of C?H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O?.) is an important species in C?H activation. The mechanistic details of C?H activation by O?. radicals can be well understood by studying the reactions between O?. containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n‐butane was studied by using a high‐resolution time‐of‐flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n‐butane by (Sc2O3)NO? (N=1–18) clusters was observed. The reactivity of (Sc2O3)NO? (N=1–18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13?) and 12 (Sc24O37?). Larger (Sc2O3)NO? clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)NO? (N=1–5) clusters, which were found to contain the O?. radicals as the active sites. The local charge environment around the O?. radicals was demonstrated to control the experimentally observed size‐dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O?. containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C?H bond activation. 相似文献
967.
Calcite Microneedle Arrays Produced by Inorganic Ion‐Assisted Anisotropic Dissolution of Bulk Calcite Crystal
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Xia Long Ruijie Meng Weike Wu Prof. Yurong Ma Prof. Dong Yang Prof. Limin Qi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4264-4272
Besides studies on the mineralization process, research on the demineralization of minerals provides another way to understand the crystallization mechanism of biominerals and fabricate crystals with complicated morphologies. The formation of ordered arrays of c‐axis‐oriented calcite microneedles with a tri‐symmetric structure and lengths of more than 20 μm was realized on a large scale for the first time through anisotropic dissolution of calcite substrates in undersaturated aqueous solution in the presence of ammonium salts. The lengths and the aspect ratios of the calcite microneedles can be tuned by simply changing the concentrations of the ammonium salts and the dissolution time. The shape of the transverse cross sections of the calcite microneedles obtained in the presence of NH4Cl and NH4Ac is almost regularly triangular. The tri‐symmetric transverse cross‐section geometry of the calcite microneedles could be attributed to the tri‐symmetric feature of rhombohedral calcite atomic structures, the synergetic interactions between electrostatic interaction of ammonium ions and dangling surface carbonate groups, and the ion incorporation of halide ions. 相似文献
968.
A New Class of Tunable Dendritic Diphosphine Ligands: Synthesis and Applications in the Ru‐Catalyzed Asymmetric Hydrogenation of Functionalized Ketones
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Dr. Baode Ma Tingting Miao Yihua Sun Yanmei He Dr. Ji Liu Dr. Yu Feng Prof. Dr. Hui Chen Prof. Dr. Qing‐Hua Fan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9969-9978
A series of tunable G0–G3 dendritic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β‐ketoesters, α‐ketoesters, and α‐ketoamides to reveal the effects of dendron size on the catalytic properties. The second‐ and third‐generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first‐generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second‐generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity. 相似文献
969.
Efficient Copper‐Catalyzed Direct Intramolecular Aminotrifluoromethylation of Unactivated Alkenes with Diverse Nitrogen‐Based Nucleophiles
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Dr. Jin‐Shun Lin Ya‐Ping Xiong Can‐Liang Ma Li‐Jiao Zhao Prof. Dr. Bin Tan Prof. Dr. Xin‐Yuan Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(5):1332-1340
A mild, convenient, and step‐economical intramolecular aminotrifluoromethylation of unactivated alkenes with a variety of electronically distinct, nitrogen‐based nucleophiles in the presence of a simple copper salt catalyst, in the absence of extra ligands, is described. Many different nitrogen‐based nucleophiles (e.g., basic primary aliphatic and aromatic amines, sulfonamides, carbamates, and ureas) can be employed in this new aminotrifluoromethylation reaction. The aminotrifluoromethylation process allows straightforward access to diversely substituted CF3‐containing pyrrolidines or indolines, in good to excellent yields, through a direct difunctionalization strategy from the respective acyclic starting materials. Mechanistic studies were conducted and a plausible mechanism was proposed. 相似文献
970.
Copper‐Catalyzed One‐Pot Denitrogenative–Dehydrogenative–Decarboxylative Coupling of β‐Ketoacids with Trifluorodiazoethane: Facile Access to Trifluoromethylated Aldol Products
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Dr. Heng‐Ying Xiong Zhen‐Yan Yang Zhen Chen Jun‐Liang Zeng Dr. Jing Nie Prof. Jun‐An Ma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(27):8325-8329
A novel copper‐catalyzed one‐pot cross‐coupling of β‐ketoacids with in situ generated trifluorodiazoethane has been developed. This reaction provides a direct and efficient method, in which one C?C bond and one C?O bond were formed in a carbenoid center with concomitant denitrogenation–dehydrogenation–decarboxylation, to afford trifluoromethylated aldol products. In several preliminary experiments, good to high enantioselectivities were also obtained. 相似文献