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71.
72.
A study is presented of adiabatic and non-adiabatic corrections to the dissociation energies and bond lengths of H+ 2, D+ 2 and HD+ in vibration-rotation levels of their ground electronic states, with particular attention to isotopic scaling. In previous work (MOSS, R. E., 1999, Molec. Phys., 97, 1) on rotationless levels, an anomalous non-adiabatic correction to the bond length was found for v = 20, N = 0 of HD+. Other levels close to dissociation are identified that display anomalous non-adiabatic corrections to the dissociation energies and to the bond lengths. The source of these anomalies is discussed. 相似文献
73.
C. Destrade H. T. Nguyen C. Alstermark G. Lindsten M. Nilsson B. Otterholm 《Molecular Crystals and Liquid Crystals》2013,570(2):265-280
Four series of biforked or polycatenar mesogens derived from 3,4-dialkoxycinnamic or 3-(3′,4′-dialkoxyphenyl)propanoic acids are described. These derivatives exhibit an extremely complex polymorphism including lamellar and columnar mesophases as well as nematic and cubic and some unidentified phases. X-Ray measurements have given the first evidence for a thermotropic rhombohedral mesophase. The relationships between the polymorphism and molecular structure are discussed. 相似文献
74.
E. P. Pozhidayev L. M. Blinov L. A. Beresnev V. V. Belyayev 《Molecular Crystals and Liquid Crystals》2013,570(1):359-377
A pyro-electric technique is developed which allows the measurement of the dielectric response near the A*-C* phase transition in ferroelectric liquid crystals. The temperature dependence of the elastic modulus K θ(T) corresponding to the molecular tilt in smectic layers is calculated from the experimental data. Direct pyro-electric measurements of the relaxation time for the spontaneous polarization P s and the data on K θ(T) allow us to calculate the temperature behaviour of the twist-viscosity γ1(T) for the smectic C* phase. The curves γ1(T) are compared for the smectic C* and the nematic phase of the same compound and the dependence of the twist viscosity on the molecular tilt angle in the C* phase is investigated. The results of the dielectic measurements are discussed in terms of the mean-field approximation. 相似文献
75.
Polar Order and Symmetry Breaking at the Boundary between Bent‐Core and Rodlike Molecular Forms: When 4‐Cyanoresorcinol Meets the Carbosilane End Group 下载免费PDF全文
Dr. Eduard Westphal Prof. Dr. Hugo Gallardo Prof. Dr. Giovanni Finoto Caramori Dr. Nerea Sebastián Dr. Maria‐Gabriela Tamba Dr. Alexey Eremin Prof. Dr. Susumu Kawauchi Dr. Marko Prehm Prof. Dr. Carsten Tschierske 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(24):8181-8197
Two isomeric achiral bent‐core liquid crystals involving a 4‐cyanoresorcinol core and containing a carbosilane unit as nanosegregating segment were synthesized and were shown to form ferroelectric liquid‐crystalline phases. Inversion of the direction of one of the COO groups in these molecules leads to a distinct distribution of the electrostatic potential along the surface of the molecule and to a strong change of the molecular dipole moments. Thus, a distinct degree of segregation of the carbosilane units and consequent modification of the phase structure and coherence length of polar order result. For the compound with larger dipole moment ( CN1 ) segregation of the carbosilane units is suppressed, and this compound forms paraelectric SmA and SmC phases; polar order is only achieved after transition to a new LC phase, namely, the ferroelectric leaning phase (SmCLsPS) with the unique feature that tilt direction and polar direction coincide. The isomeric compound CN2 with a smaller dipole moment forms separate layers of the carbosilane groups and shows a randomized polar SmA phase (SmAPAR) and ferroelectric polydomain SmCsPS phases with orthogonal combination of tilt and polar direction and much higher polarizations. Thus, surprisingly, the compound with the smaller molecular dipole moment shows increased polar order in the LC phases. Besides ferroelectricity, mirror‐symmetry breaking with formation of a conglomerate of macroscopic chiral domains was observed in one of the SmC phases of CN1 . These investigations contribute to the general understanding of the development of polar order and chirality in soft matter. 相似文献
76.
3-Cyano thiophene-centred π-conjugated mesogens with alkoxy phenyl/biphenyl rings are synthesised by palladium acetate-catalysed direct arylation to investigate the mesophase properties and the molecular order. The synthesised mesogens mostly exhibit smectic A mesophase as confirmed by X-ray diffraction studies. Further, due to the manifestation of π-conjugated core, the mesogens exhibit photo luminescence in solution with emission maxima in the range 425–460 nm. Density functional theory and time-dependent density functional theory calculations of a representative mesogen indicate possible intramolecular charge transfer transition between the biphenyl to 3-cyanothiophene units. Despite structural simplicity, the observation of smectic A phase is attributed to location of strong dipole moment component perpendicular to the long axis of the molecules due to the presence of polar cyano group at 3-position of central thiophene ring. The 13C NMR studies are performed in mesophase and using the 13C–1H dipolar couplings determined from 2D separated local field experiment; the order parameters of central thiophene ring and side arm phenyl rings are calculated. Moreover, the order parameter ratios of thiophene and side arm phenyl rings indicate the bent–core nature of the mesogen. 相似文献
77.
78.
A new and simple series of side-chain liquid crystalline polymethacrylates containing biphenyl hemiphasmidic mesogens based on 4-[(3,4,5-trialkan)-1-carbonylbenzoate]biphenyl (denoted as PTmBMA, m = 6, 8, 10, 12, 14, 16, 18, m refers to the carbon number of alkoxy tails) groups was designed and successfully synthesised via free radical polymerisation. The phase structures and transitions of the polymers were investigated by the combination of techniques including differential scanning calorimetry, polarizing microscope, one-dimensional/two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering. The experimental results revealed that the liquid crystalline phase structures and behaviours of the polymers were found to be strongly dependent on the alkyl tail length (m). When m = 6, the PTmBMA formed a stable smectic phase above Tg. When m = 8, 10, 12, 14, 16, 18, the sample presented a hexagonal columnar mesophase (Φh), suggesting that the alkyl length has played an important role in the phase behaviours of hemiphasmidic side-chain liquid crystalline polymers. 相似文献
79.
Ghassan Q. Ali 《Liquid crystals》2018,45(3):421-430
In this study, a new series of non-symmetrically 3,5-disubstituted of 1,2,4-oxadiazole derivatives, 4-[5-(4-methylphenyl)-1,2,4-oxadiazol-3-yl]-phenyl-4-alkoxybenzoate (G1–G11), which containing ether and ester linkages in the same molecule, is synthesized using different synthetic procedures and their structures are confirmed by several spectroscopic techniques (FT-IR and 1H nuclear magnetic resonance). The mesomorphic properties of these compounds are studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM); all these derivatives exhibited as mesogens and displayed an enantiotropic liquid crystal with nematic texture, the nematogenic phase of these materials was appeared in wide temperature ranges on heating and cooling cycles that were observed by POM and DSC. The influence of 1,2,4-oxadiazole ring and the elongation of alkyl chain in the mesomorphic properties of this series were investigated. The mesogenic behaviour of this series was compared with the compounds possessing a somewhat similar structure. 相似文献
80.
Several calamitic reactive mesogens containing only two benzene rings in the molecular core and with or without lateral substitution by the methyl/methoxy groups have been designed and their mesomorphic behaviour was characterised. Depending on the molecular structure, some of the materials exhibit the nematic and the orthogonal smectic mesophases. The reactive mesogens are aimed for further design of the macromolecular materials like polysiloxane-based polymers and elastomers. Beyond the mesomorphic and structural properties, the electrorheological properties within the temperature range of the nematic and smectic A mesophases were studied with and without applied electric field for the selected reactive mesogen. The increase of viscosity was found not to be higher than three times under applied electric field strength of 2 kV/mm. The mesomorphic, structural and rheological properties of the newly designed reactive mesogens are discussed in order to contribute to better understanding of the molecular architecture–nano-organisation properties relationship of such mesogenic materials. 相似文献