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排序方式: 共有121条查询结果,搜索用时 15 毫秒
1.
Nitin P. Lobo K.V. Ramanathan T. Narasimhaswamy 《Magnetic resonance in chemistry : MRC》2020,58(11):988-1009
In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one- and two-dimensional (2D) solid-state 13C nuclear magnetic resonance (NMR) spectroscopy are described. Besides 13C chemical shifts, the 13C─1H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the 13C─1H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B1 and B2 mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state 13C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed. 相似文献
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The cyclization of 1‐amino‐2‐mercapto‐5‐[1‐(4‐ethoxyphenyl)‐5‐methyl‐1,2,3‐triazol‐4‐yl]‐1,3,4‐triazole which was synthesized from p‐ethoxyaniline with various triazole acid in absolute phosphorus oxychloride yields 3,6‐bis(1,2,3‐triazolyl)‐s‐triazolo[3,4‐b]‐1,3,4‐thiadiazole derivatives 9a?j , and their structures are established by MS, IR, CHN and 1H NMR spectral data. 相似文献
4.
Controlling domain orientation of liquid crystalline block copolymer in thin films through tuning mesogenic chemical structures
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He‐Lou Xie Xiao Li Jiaxing Ren Camille Bishop Christopher G. Arges Paul F. Nealey 《Journal of Polymer Science.Polymer Physics》2017,55(6):532-541
Controlling the macroscopic orientation of nanoscale periodic structures of amphiphilic liquid crystalline block copolymers (LC BCPs) is important to a variety of technical applications (e.g., lithium conducting polymer electrolytes). To study LC BCP domain orientation, a series of LC BCPs containing a poly(ethylene oxide) (PEO) block as a conventional hydrophilic coil block and LC blocks containing azobenzene mesogens is designed and synthesized. LC ordering in thin films of the BCP leads to the formation of highly ordered, microphase‐separated nanostructures, with hexagonally arranged PEO cylinders. Substitution on the tail of the azobenzene mesogen is shown to control the orientation of the PEO cylinders. When the substitution on the mesogenic tails is an alkyl chain, the PEO cylinders have a perpendicular orientation to the substrate surface, provided the thin film is above a critical thickness value. In contrast, when the substitution on the mesogenic tails has an ether group the PEO cylinders assemble parallel to the substrate surface regardless of the film thickness value. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 532–541 相似文献
5.
The compound 4 propyl paraethoxy phenyl cyclohexyl carboxylate (code name D302) is a member of a homologous series and exhibits liquid crystalline (nematic) behavior in the temperature range 48°C to 78°C. An experiment has been set up for conducting X-ray studies of liquid crystal samples at various temperatures. From X-ray studies conducted at different temperatures on D302, the apparent molecular length and inter-molecular distance and their temperature dependence have been determined. The variation of the orientational-order parameter <P2>xray has been determined from the intensities of the scanned X-ray photographs taken at different temperatures. The results have been compared with the<P2>opt values obtained by us from birefringence studies. 相似文献
6.
Koyuki Sakai Hiroki Nishiyama Shinsuke Inagi Ikuyoshi Tomita Yusuke Hibi Motonori Komura Keiji Nose Tomokazu Iyoda 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):E1-E8
A block copolymer composed of a flexible polar poly(ethylene glycol) (PEG) and a less polar liquid crystalline poly(allene) segments is prepared by the living coordination polymerization of an allene derivative possessing trans‐azobenzene‐containing mesogenic substituent by the use of a π‐allylnickel macroinitiator bearing PEG segment. The thin film of the block copolymer is prepared by the spin coating of its solution onto mica or silicon wafer which proves to possess perpendicularly oriented nanocylindrical microphase separated structures as supported by the differential calorimetric, polarized optical microscopic, grazing‐incidence small‐angle X‐ray scattering, transmission electron microscope, and atomic force microscope measurements. 相似文献
7.
Manea S. AlKhalifah Chunhong Lei Steven A. Myers Stuart P. Kitney 《Liquid crystals》2013,40(3):402-417
The cross-linking of polymerisable liquid crystalline semiconductors is a promising approach to solution-processable, multilayer, organic photovoltaics. Here we demonstrate an organic bilayer photovoltaic with an insoluble electron-donating layer formed by cross-linking a nematic reactive mesogen. We investigate a range of perylene diimide (PDI) materials, some of which are liquid crystalline, as the overlying electron acceptor layer. We find that carrier mobility of the acceptor materials is enhanced by liquid crystallinity and that mobility limits the performance of photovoltaic devices. 相似文献
8.
The photo-optical behaviour of two series of chiral photochromic acrylic copolymers with a chiral nematic phase has been studied. These copolymers contain identical chiral photochromic units, but have different structures of the phenyl benzoate mesogenic side groups which are responsible for the development of LC phases. This approach allowed us to examine specific features of the photo-optical behaviour of the copolymers as a function of the nature of the LC 'matrix' in which the cholesteric phase was induced. The action of UV irradiation was shown to lead to the E-Z isomerization of the chiral side groups and, as a consequence, to untwisting of the cholesteric helix of the copolymers. For copolymers of both series, the effective quantum yields of this photochemical process were calculated. In the case of copolymers in which the cholesteric mesophase is induced in a smectogenic matrix, the corresponding values of the quantum yield are lower and depend slightly on temperature. A plausible explanation of the above phenomena is suggested. 相似文献
9.
Takuya Adachi Yasuhisa Yamamura Mafumi Hishida Mao Ueda Shunji Ito 《Liquid crystals》2013,40(11):1340-1344
Molecular dynamics in the soft crystal, E phase of 6-octyl-2-phenylazulene was studied by X-ray diffraction, and dielectric and Fourier transform infrared spectroscopies. Clear dielectric dispersion is observed due to the head-to-tail disordering in a kHz range around 400 K. The CH stretching frequencies exhibit more pronounced shifts at the phase transition point from the high-temperature ordered crystal to the E phase than that at the melting from the E phase to the isotropic liquid. The results are discussed in comparison with a typical E series, 4-n-alkyl-4′-isothiocyanatobiphenyl (n being the number of carbon atoms in the alkyl group). 相似文献
10.
A new ferroelectric liquid crystal, 1-ethylpropyl (S)-2-[2-fluoro-4-(4′-decyloxybiphenylcarbonyloxy) benzoyloxy] propanoate, F, was synthesized and mixed with an achiral swallow-tailed material, 2-propylpentyl 4-(4′-nonyloxybiphenyl-4-carbonyloxy) benzoate,P, for the preparation of binary mixtures for the study. The binary mixtures gave a phase sequence SmA* -SmC* -SmX*. The electro-optic response of the mixtures in the ferroelectric SmC* phase was investigated. V-shaped switching was observed as the amount of the achiral swallow-tailed material became greater than 20 wt %. This result suggests that thresholdless, V-shaped switching in ferroelectric liquid crystal mixtures can be achieved by mixing a ferroelectric liquid crystal with an achiral swallow-tailed compound. 相似文献