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排序方式: 共有361条查询结果,搜索用时 93 毫秒
1.
Functional Carbazole Liquid‐Crystal Block Codendrimers with Optical and Electronic Properties
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Ismael Gracia Beatriz Feringán Prof. José Luis Serrano Dr. Roberto Termine Dr. Attilio Golemme Dr. Ana Omenat Prof. Joaquín Barberá 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(3):1359-1369
The synthesis and characterisation of a family of block codendrimers consisting of highly versatile mesogenic and carbazole‐containing 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) dendrons are reported. The liquid‐crystal behaviour was investigated by means of differential scanning calorimetry, polarised‐light optical microscopy and X‐ray diffraction. Depending on the chemical structure of the constituent dendrons, the codendrimers show lamellar or columnar mesophases. On the basis of the experimental results, models both at the molecular level and in the mesophase are proposed. The physical properties of the block codendrimers derived from the presence of the carbazole moiety in their structure were investigated: photoluminescence in solution and in the mesophase, electrochemical behaviour and hole transport. Electrodeposition of carbazole dendrons afforded a globular supramolecular conformation in which the mesogenic molecular side plays a key role. 相似文献
2.
S. S. Banerjee S. Goldberg Y. Myasoedov M. Rappaport E. Zeldov A. Soibel F. de la Cruz J. van der Beek M. Konczykowski T. Tamegai V. Vinokur 《Pramana》2006,66(1):43-54
Disorder and porosity are parameters that strongly influence the physical behavior of materials, including their mechanical,
electrical, magnetic and optical properties. Vortices in superconductors can provide important insight into the effects of
disorder because their size is comparable to characteristic sizes of nanofabricated structures. Here we present experimental
evidence for a novel form of vortex matter that consists of inter-connected nanodroplets of vortex liquid caged in the pores
of a solid vortex structure, like a liquid permeated into a nanoporous solid skeleton. Our nanoporous skeleton is formed by
vortices pinned by correlated disorder created by high-energy heavy ion irradiation. By sweeping the applied magnetic field,
the number of vortices in the nanodroplets is varied continuously from a few to several hundred. Upon cooling, the caged nanodroplets
freeze into ordered nanocrystals through either a first-order or a continuous transition, whereas at high temperatures a uniform
liquid phase is formed upon delocalization-induced melting of the solid skeleton. This new vortex nanoliquid displays unique
properties and symmetries that are distinct from both solid and liquid phases. 相似文献
3.
《Chemphyschem》2002,3(12):1024-1030
N,N,N‐butylethylpentylpropylammonium iodide 4 and related molecules have been selectively synthesised from commercially available aldehydes, amines and alkyl iodides using a reductive alkylation procedure. The crystalline texture of 4 obtained on cooling is optically isotropic between crossed polarisers, indicating a cubic structure. Differential scanning calorimetry (DSC, +10 K min?1) reveals a glass phase transition at ?59 °C and a melting point at 192 °C. The melting entropy (23.9 J mol?1 K?1) indicates a first‐order transition between a highly disordered mesophase and the isotropic liquid. Powder X‐ray diffraction patterns were indexed in the cubic system (a=14.08Å; Pm n space group). In this cell, the molecular packing with Z=6 corresponds to a rather low compactness of 65 %. Iodine and tetraalkylammonium ions occupy positions with a m2 site symmetry. These highly symmetrical states may be generated by stepwise rotation of the ammonium cation. The same structural model for orientationally disordered crystal (ODIC) phases can be applied to a series of tetraalkylammonium bromides and iodides. 相似文献
4.
Basurto S García S Neo AG Torroba T Marcos CF Miguel D Barberá J Ros MB de la Fuente MR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(18):5362-5376
Several new liquid-crystalline indene and pseudoazulene systems are reported. These molecules give rise to either columnar hexagonal mesophases and/or columnar plastic phases. The unique nature of these compounds stems from their non-classical discotic structure. Although the molecules have rigid aromatic cores, they lack terminal tails and instead the polarizable atoms (S, halogens) or polar groups (CN, CO) act as unusual soft parts. On the basis of many structurally related materials, we conclude that for this type of compound molecular stacking in the solid state is a prerequisite for the appearance of a columnar mesophase, although other intermolecular interactions within the layers are also important in establishing liquid-crystalline order. The behavior reported for these mesomorphic molecules opens up new possibilities in the search for related molecular interactions that might be useful for the construction of supramolecular architectures with particular properties. 相似文献
5.
A class of extended 2,5‐disubstituted‐1,3,4‐oxadiazoles R1‐C6H4‐{OC2N2}‐C6H4‐R2 (R1=R2=C10H21O 1 a , p‐C10H21O‐C6H4‐C?C 3 a , p‐CH3O‐C6H4‐C?C 3 b ; R1=C10H21O, R2=CH3O 1 b , (CH3)2N 1 c ; F 1 d ; R1=C10H21O‐C6H4‐C?C, R2=C10H21O 2 a , CH3O 2 b , (CH3)2N 2 c , F 2 d ) were prepared, and their liquid‐crystalline properties were examined. In CH2Cl2 solution, these compounds displayed a room‐temperature emission with λmax at 340–471 nm and quantum yields of 0.73–0.97. Compounds 1 d , 2 a – 2 d , and 3 a exhibited various thermotropic mesophases (monotropic, enantiotropic nematic/smectic), which were examined by polarized‐light optical microscopy and differential scanning calorimetry. Structure determination by a direct‐space approach using simulated annealing or parallel tempering of the powder X‐ray diffraction data revealed distinctive crystal‐packing arrangements for mesogenic molecules 2 b and 3 a , leading to different nematic mesophase behavior, with 2 b being monotropic and 3 a enantiotropic in the narrow temperature range of 200–210 °C. The structural transitions associated with these crystalline solids and their mesophases were studied by variable‐temperature X‐ray diffractometry. Nondestructive phase transitions (crystal‐to‐crystal, crystal‐to‐mesophase, mesophase‐to‐liquid) were observed in the diffractograms of 1 b, 1 d , 2 b, 2 d , and 3 a measured at 25–200 °C. Powder X‐ray diffraction and small‐angle X‐ray scattering data revealed that the structure of the annealed solid residue 2 b reverted to its original crystal/molecular packing when the isotropic liquid was cooled to room temperature. Structure–property relationships within these mesomorphic solids are discussed in the context of their molecular structures and intermolecular interactions. 相似文献
6.
The triangular phase diagram of the system dodecyltri-methylammonium hydroxide (DTAOH)–dodecanephosphonic acid (H2DP)–water was studied by several techniques. The DTAOH-rich zone could not be studied because DTAOH decomposed when it was
dried. Pure H2DP only forms lamellar mesophases with water. The inclusion of DTAOH in the system produces the appearance of cubic and hexagonal
mesophases. The gradual increase in DTAOH proportion lead to the gradual reduction in the existence of the lamellar mesophase
domain, and increase of the hexagonal liquid crystal domain. At high DTAOH content, the lamellar mesophase disappeared. This
behavior was explained by the gradual destruction of the hydrogen-bonded structure in the polar headgroup layer of liquid
crystal aggregates. H2DP-rich anhydrous crystals were triclinic.
Received: 8 September 1997 Accepted: 17 February 1998 相似文献
7.
苯并菲盘状液晶的合成、亲氟效应及分子对称性对介晶性的影响 总被引:3,自引:0,他引:3
New symmetrical and asymmetrical triphenylene-containing discotic liquid crystals with two different peripheral alkyl chains, known as sym-TP(OC6H13)3(OR)3 and asym-TP(OC6H13)3(OR)3, were synthesized. Their thermotropic liquid crystal properties were investigated through polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. The asyrranetdcal discogens are 2,6,11-rialkoxy-3,7,10-trihexyloxytriphenylenes, with the alkyl chain carbon numbers varying from 3-10, 12, and 14, while the symmetrical compounds are 2,6,10-trialkyloxy-3,7,11-trihexyloxytriphenylene. Two fluoroalkoxy substituted triphenylene discogens, 2,6,10-td(4,4,4-trifluorobutoxy)-3,7,11-trihexyloxytriphenylene and its asymmetrical isomer 2,6,11-tri(4,4,4-trifluorobutoxy)-3,7,10-trihexyloxytdphenylene were prepared. These two compounds show higher melting and clearing points than their alkoxy analogs, which implies that fluorophilic effect exists in the formation and stabilization of discotic columnar mesophase. The triphenylene derivatives TP(OC6H13)3(OR)3 with two different peripheral chains, symmetrically or asymmetrically attached on triphenylene cores, have lower melting points and clearing points than those of the higher symmetrical compounds TP(OR)6 with the same total chain carbon numbers. The mixed-chain-triphenylenes with longer alkoxy chains (n=9,10,12,14) show columnarmesophase at room temperature. 相似文献
8.
Verónica Iguarbe 《Liquid crystals》2020,47(2):301-308
ABSTRACT Novel liquid crystalline Janus dendrimers that combine a mesogenic block and an electroactive block have been synthesised. The mesogenic block is based on two third-generation Percec-type dendrons bearing six or eight terminal dodecyloxy alkyl chains, whereas the electroactive blocks are formed by one or two carbazole units. The liquid crystal behaviour was investigated by polarised-light optical microscopy, differential scanning microscopy and X-ray diffraction. The Janus dendrimers with one electroactive unit exhibited cubic or columnar liquid crystal phases, whereas the Janus dendrimers with two electroactive units did not show liquid crystalline behaviour. The UV-vis absorption and emission properties of the Janus dendrimers were investigated. The spectra suggested the existence of π-π stacking and the formation of aggregates in the solid state. Electrodeposition of the carbazole-containing dendrimers afforded semi-globular particles in which the number of electropolymerizable units and the flexible or rigid character of the linker have a decisive influence in the particle size. 相似文献
9.
The morphologically undifferentiated cells of nonregenerant callous tissue of Cereus peruvianus cultured in the original medium and in medium supplemented with tyrosine were used as an alkaloid source. Comparison of alkaloid
production by C. peruvianus plants and by callous tissues indicated that alkaloid levels were almost twice as high in callous tissues as in shoots of
C. peruvianus plants. The ratio of alkaloid concentration between mature plant and morphologically und ifferentiated cells of callous tissue
was 1∶1.7. A relationship between culture medium containing tyrosine and alkaloid production was also observed in the callous
tissues of C. peruvianus. Since increased alkaloid production may be induced by additional factors such as tyrosine, increasing levels of tyrosine
or other conditions of the culture medium may be considered factors for inducing higher alkaloid production by C. peruvianus callous tissues. 相似文献
10.
Professor J. W. Doane 《Liquid Crystals Today》2013,22(2):13-14
Abstract Stanford Resources Inc., the leading market research firm specializing in the global electronic display industry, has released its annual study on the flat panel display (FPD) industry - Flat lnformation Displays. Now in its eighth edition, this industry perspective analyses competing FPD technologies in terms of technological development, sales, suppliers and future prospects. 相似文献