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Systematic Electronic Control in Ambipolar Compounds Optimizes Their Photoluminescence Properties: Synthesis, Characterization, and Device Fabrication of Four-Coordinate Boron Compounds Containing an N,O-Chelating Oxazolylphenolate Ligand
Son, Ho-Jin,Han, Won-Sik,Wee, Kyung-Ryang,Chun, Ji-Yun,Choi, Kyu-Bum,Han, Su Jung,Kwon, Soon-Nam,Ko, Jaejung,Lee, Chongmok,Kang, Sang Ook WILEY-VCH Verlag 2009 European journal of inorganic chemistry Vol.2009 No.11
<P>A series of four-coordinate boron compounds of the type N,O-(OPh<SUP>OxZ</SUP>ArX)BPh<SUB>2</SUB> or N,O-(OPh<SUP>OxZ</SUP>NPh<SUB>2</SUB>)BPh<SUB>2</SUB> (5a–g) has been prepared by treating triphenylboron (TPB) with2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-4-X-arylphenols(HOPh<SUP>OxZ</SUP>ArX; 4a–f) or 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-4-(4-diphenylamino)phenol (HOPh<SUP>OxZ</SUP>NPh<SUB>2</SUB>; 4g). A systematic change in the electronic structures is achieved in these compounds by incorporating electron-withdrawing (EW) and -donating (ED) groups [ArX (X = 4-cyano-, 2,4-difluoro-, 4-chloro-, phenyl, 4-methoxy-, and 4-dimethylaminophenyl) or NPh<SUB>2</SUB>] at the 4-position of the phenoxide. The absorption and emission maxima of the ED groups show a significant red-shift compared to those observed in the EW groups. This red-shift suggests that π-conjugation is effectively extended over the arylphenoxides and oxazoline moiety once the boron center has been plugged into the corresponding ligands. The gradual decrease observed in the bandgaps on going from EW to ED groups is found to be in agreement with the increase in oxidation potentials determined by the cyclic voltammetry (CV) experiments. In particular, a Hammet plot between the EW and ED substituents and oxidation potentials confirms the ground state electronic perturbation. Such alterations are attributed mainly to an elevation of the energy levels of the HOMOs), as further confirmed by a series of theoretical calculations on the frontier orbitals of each system. The ED group (-NPh<SUB>2</SUB>) substituted compound 5g shows a bipolar character due to intramolecular charge transfer in the complex, with the highest photoluminescence quantum yield being obtained in toluene. This new boron complex was found to function as an emitter in electroluminescence (EL) devices, with a maximum brightness of 2905 cd/m<SUP>2</SUP> at 13 V and a current efficiency of 1.63 cd/A at 6 mA/cm<SUP>2</SUP>, with a turn-on voltage of 4.3 V.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)</P> <B>Graphic Abstract</B> <P>A series of electron-push and -pull aryl-substituted oxazolylphenolate ligands is synthesized and used to prepare boron compounds. The photophysical properties of these boron compounds are evaluated,and the corresponding EL properties studied through device fabrication by using them as emitting materials in a multilayer device. <img src='wiley_img/14341948-2009-2009-11-EJIC200900017-fig000.gif' alt='wiley_img/14341948-2009-2009-11-EJIC200900017-fig000'> </P>
<P>A series of porphyrins, M[TCPP-Et<SUB>4</SUB>] [M = Zn (1), Cu (2), and Ni (3); Et = CH<SUB>2</SUB>CH<SUB>3</SUB>; TCPP = meso-tetra(4-carboxyphenyl)porphyrin], M[TCPP-Me<SUB>4</SUB>] [M = Zn (4), Cu (5), and Co (6); Me = CH<SUB>3</SUB>], and two nonmetalated compounds, TCPP-Et<SUB>4</SUB> (7) and TCPP-Me<SUB>4</SUB>·H<SUB>2</SUB>O (8), were synthesized by solvothermal reactions and characterized by single-crystal X-ray diffraction. Compounds 1–3 feature an isolated structure with a planar macrocycle and an embedded metal-ion coordinating to four pyrrole nitrogen atoms. Compound 4 is characterized as a two-dimensional coordination polymer, and the zinc ion coordinates to four nitrogen atoms and two oxygen atoms. Compound 4 possesses a large void space (361 Å<SUP>3</SUP>), which corresponds to 14 % of the unit-cell volume. Compounds 5 and 6 are characteristic of an isolated motif with a four-coordinate metal ion and a saddle-distorted nonplanar porphyrin macrocycle. Nonmetalated compounds 7 and 8 also show an isolated structure with a planar macrocycle. For compounds 1–3 and 7, the TCPP is esterified with ethanol, while for compounds 4–6 and 8, the TCPP is esterified with methanol. The molecules in 1 and 6–8 are interconnected by hydrogen bonds and π–π interactions to yield 3D supramolecular networks, while in 2–5, 2D supramolecular motifs are formed. The reaction mechanism was explored. Esterification plays an important role in changing the properties of the compounds as well as in the formation of different structural motifs and supramolecular networks. The UV/Vis, FTIR, fluorescence, phosphorescence, and MALDI-TOF MS spectra, quantum yields, luminescence lifetimes, and cyclic voltammograms were also studied in detail.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)</P> <B>Graphic Abstract</B> <P>Eight esterified TCPP compounds were successfully synthesized by solvothermal reactions and characterized. The reaction mechanism was investigated. Esterification plays a vital role in the properties, structural motifs and supramolecular networks. <img src='wiley_img/14341948-2009-2009-36-EJIC200900801-fig000.gif' alt='wiley_img/14341948-2009-2009-36-EJIC200900801-fig000'> </P>
<P>Catalytically inactive, latent Ru–carboxylate complex 2, which was recently serendipitously isolated, can be activated in situ efficiently in ionic liquids (ILs) with the aid of imidazolium halides or tetrabutylammonium halides. The activity of the in situ activated catalyst was largely dependent on IL anions, imidazolium halides, and terabutylammonium halides. Under the optimal condition of 1.0 mol-% of [bmim][Br] in CH<SUB>2</SUB>Cl<SUB>2</SUB>/[bmim][SbF<SUB>6</SUB>] (1:1), latent Ru complex 2 was activated in situ to catalyze the ring-closing metathesis of various dienes with conversions of up to >99 %. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)</P> <B>Graphic Abstract</B> <P>Ionic liquid as an activator for latent Ru complex: Latent Ru–carboxylate complex 2 can be activated in situ in the presence of an equivalent amount of [bmim][Br] in the ionic liquid [bmim][SbF<SUB>6</SUB>] and used to catalyze the ring-closing metathesis of various dienes with conversions of up to >99 %. <img src='wiley_img/1434193X-2009-2009-14-EJOC200801214-fig000.gif' alt='wiley_img/1434193X-2009-2009-14-EJOC200801214-fig000'> </P>
<P>A versatile method for the total synthesis of cyclic diphenyl ether-type diarylheptanoids, acerogenin C, acerogenin L, (±)-galeon, and (±)-pterocarine was described. The Ullmann reaction of suitably substituted linear diphenylheptanoids was employed for the intramolecular formation of the key ether intermediates as the final step. The prerequisite diarylheptanoids were prepared by a series of cross-aldol condensation reactions from readily available starting benzaldehydes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)</P> <B>Graphic Abstract</B> <P> <img src='wiley_img/1434193X-2007-2007-8-EJOC200600938-fig000.gif' alt='wiley_img/1434193X-2007-2007-8-EJOC200600938-fig000'> </P>
<P>The ring-forming dimerizations of enynes were catalyzed by the first-generation carbene ruthenium complex, and the effects of the catalysts and ethylene gas were studied. The deprotection of propargyl ethers by the carbene ruthenium complexes is the first to be reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)</P> <B>Graphic Abstract</B> <P> <img src='wiley_img/1434193X-2005-2005-1-EJOC200400630-fig000.gif' alt='wiley_img/1434193X-2005-2005-1-EJOC200400630-fig000'> </P>
<P>Electrochemical oxidation was performed during the organocatalyzed α-oxyamination of aldehydes by using a one-compartment electrolytic cell under galvanostatic conditions. In the presence of substoichiometric amounts of sec-amines, the desired coupling products were formed in good yield. The asymmetric variant of the α-oxyamination of aldehydes was examined by using chiral sec-amines. Control experiments and cyclic voltammetry confirmed the key intermediate of this reaction to be the cationic radical of the enamine derived from the sec-amine catalysts and aldehydes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)</P> <B>Graphic Abstract</B> <P>Anodic oxidation was used to promote the organocatalyzed α-oxyamination of aldehydes. Under galvanostatic conditions, cationic radical intermediates are formed as key intermediates. Cyclic voltammetry and control experiments were carried out to confirm the proposed intermediates and the mechanism of the reaction. <img src='wiley_img/1434193X-2009-2009-31-EJOC200900871-fig000.gif' alt='wiley_img/1434193X-2009-2009-31-EJOC200900871-fig000'> </P>
<P>A new tp-bridged complex [Ni(pyrazole)<SUB>4</SUB>(tp)]<SUB>n</SUB> (1; tp = terephthalate) coordinated with a nonchelating pyrazole ligand has been synthesized and characterized using X-ray structure determination and magnetic studies. The crystal structure reveals that the capping ligand functions as a source of hydrogen bonding and intermolecular contacts, such as π–π and CH–π interactions, that result in a three-dimensional supramolecular assembly. Weak antiferromagnetic couplings are transmitted between Ni<SUP>II</SUP> centers through the tp linkage. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)</P> <B>Graphic Abstract</B> <P> <img src='wiley_img/14341948-2005-2005-23-EJIC200500526-fig000.gif' alt='wiley_img/14341948-2005-2005-23-EJIC200500526-fig000'> </P>
<P>Synthesis of tetraketide lactones 2 and 3, which are likely to be produced by a model pikromycin polyketide synthase (PKS), has been investigated. The tetraketide lactones with six-membered rings, 2a and 2b, were synthesized successfully by the asymmetric aldol reaction, allylation, and the Reformatsky reaction. The attempted synthesis of tetraketide lactones with eight-membered rings, 3a and 3b, led to the formation of the compounds 2a and 2b. The synthesis of another tetraketide lactone compounds 35 was attempted with the hope that introducing an additional methyl group would lead to a change in thermodynamic stability. However, it produced the corresponding tetraketide lactone 34 with a six-membered ring. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)</P> <B>Graphic Abstract</B> <P> <img src='wiley_img/1434193X-2007-2007-20-EJOC200700254-fig000.gif' alt='wiley_img/1434193X-2007-2007-20-EJOC200700254-fig000'> </P>
<P>Two isomeric S<SUB>2</SUB>O<SUB>2</SUB> macrocycles (L<SUP>1</SUP> and L<SUP>2</SUP>) with a 14-membered cavity have been synthesised as a model system with different binding modes. Self-assembly reactions of L<SUP>1</SUP> and L<SUP>2</SUP> with silver perchlorate afford the respective ligand-directed cyclic oligomer complexes with different shapes: a poly(bicyclic dimer) (1) and a discrete cyclic tetramer (2). The formation of these supramolecular complexes is discussed in terms of conformational discrimination of two isomeric macrocycles due to ring rigidity and interdonor distances.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)</P> <B>Graphic Abstract</B> <P> <img src='wiley_img/14341948-2006-2006-17-EJIC200600290-fig000.gif' alt='wiley_img/14341948-2006-2006-17-EJIC200600290-fig000'> </P>
<P>The synthesis of the first examples of anion receptors that utilize boron–fluoride interactions and (C–H)<SUP>+</SUP>···F<SUP>–</SUP>-type ionic hydrogen-bond interactions in the binding of F ions is reported herein. o-, m-, and p-Phenylboronic acids were linked to naphthoimidazolium through a methylene group. On the basis of fluorescence and <SUP>19</SUP>F NMR studies, we have confirmed that the addition of fluoride to a boron center occurs prior to the formation of (C–H)<SUP>+</SUP>···F<SUP>–</SUP>-type ionic hydrogen bond with the imidazolium moiety. More importantly, these investigations have demonstrated that only the receptor bearing the ortho-directed boron and imidazolium exhibits enhanced fluoride binding. The increased binding ability of the asymmetric bidentate receptor of ortho-boronic acid and imidazolium towards F<SUP>–</SUP> enables it to sense fluoride ions in a 95:5 CH<SUB>3</SUB>CN/HEPES aqueous solution. The fluorescence responses to different anions were also explored; the ortho-boron-imidazolium receptor displayed ratiometric fluorescence changes and a high selectivity towards fluoride ions over other anions (Cl<SUP>–</SUP>, Br<SUP>–</SUP>, CH<SUB>3</SUB>CO<SUB>2</SUB><SUP>–</SUP>, HSO<SUB>4</SUB><SUP>–</SUP>, and H<SUB>2</SUB>PO<SUB>4</SUB><SUP>–</SUP>).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)</P> <B>Graphic Abstract</B> <P>An asymmetric bidentate receptor containing boronic acid and an imidazolium group can recognize F<SUP>–</SUP>, as evidenced by ratiometric fluorescence responses in aqueous solution. <img src='wiley_img/1434193X-2009-2009-18-EJOC200900120-fig000.gif' alt='wiley_img/1434193X-2009-2009-18-EJOC200900120-fig000'> </P>