(S) -(-)-Ethyl Lactate as a Convenient Precursor for Synthesis of Chiral Liquid Crystals (original) (raw)
Mesomorphic and structural properties of liquid crystal possessing a chiral lactate unit
Journal of Molecular Structure, 2012
The mesomorphic and structural properties of the chiral lactic acid derivative 4 0 -(1-(octyloxy)-1-oxopropan-2-yloxy) biphenyl-4-yl 4-(decyloxy)benzoate have been studied. The compound shows the blue phase (BPII), the cholesteric (N Ã ), the TGB A and the paraelectric SmA Ã phases over a broad temperature range. Polarising optical microscopy, differential scanning calorimetry, optical transmission, X-ray diffraction and dielectric spectroscopy studies have been performed. In the SmA Ã phase the layer spacing (d) values are found to be slightly temperature dependent and suggest that there is no bi-layer association present in the mesophase. In the TGB A phase, the d values show strong temperature dependence near SmA Ã -TGB A phase transition, indicating pre-transitional effect. The temperature dependence of scattered X-ray intensities indicate the appearance of long range smectic ordering at the N Ã -TGB A phase transition. Near the TGB A -SmA Ã phase boundary strong SmA Ã fluctuations predominate. This behaviour is also observed from the temperature dependence of the d values. The transverse correlation lengths, n \ , diverge near the N Ã -TGB A phase transition indicating second order phase transition.
Molecules, 2019
Liquid crystals (LCs) are among the most prominent materials of the current information age, mainly due to their well-known application in liquid crystal displays (LCDs). Their unique electro-optical properties stem from their ability to form organised structures (mesophases) on the transition from solid state to isotropic liquid. Molecules of LCs in a mesophase still maintain the anisotropy of solid crystals, while simultaneously exhibiting the fluidity of liquids, which gives the system the ability to react immediately to external stimuli such as electric or magnetic fields, light, mechanical stress, pressure and, of course, temperature. For the proper function of LC-based devices, not only chemical, but also optical purity of materials is strongly desirable, since any impurity could be detrimental to the self-assembly of the molecules. Therefore, in this study we aimed to verify synthetic methods published in the literature, which are used nowadays to prepare chiral building blocks based on lactic acid, for their enantioselectivity. Moreover, we have focused on the development of an analytical chiral separation method for target liquid crystalline materials. Using a chiral polysaccharide-based column operated in liquid chromatography mode, we show that not all published methods of LC synthesis are enantioselective, which could lead to significant differences in the properties of the resulting materials. We show that high-performance liquid chromatography with UV detection and supercritical fluid chromatography with UV and mass spectrometry detection enable full control over the chemical and optical purity of the target LCs and the corresponding chiral building blocks. For the first time, we utilise supercritical fluid chromatography with mass detection for the direct chiral analysis of liquid crystalline materials and impurities formed during the synthesis.
Review Chiral Liquid Crystals: Structures, Phases, Effects
2014
The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.
A new synthetic approach based on (−)-menthone for chiral liquid crystals
Liquid Crystals, 2004
Starting from (2)-menthone, a new chiral building block useful for liquid crystal preparation was synthesized. This chiral moiety was attached to selected phenols under mild conditions by esterification. Rigid cores of tolanebenzoates and phenylbenzoates were prepared using the palladium cross-coupling reaction or by traditional liquid crystal synthesis methods. This convergent approach ended with a second esterification or palladium cross-coupling reaction to furnish new liquid crystal materials with smectic A, smectic C* and N* phases, as well as blue phases (BP). Thermal behavior, and the effect of chiral moiety branches and molecular packing in the smectic phases, have been investigated using differential scanning calorimetry, optical microscopy and X-ray diffraction.
Chiral Liquid Crystals: Structures, Phases, Effects
Symmetry, 2014
The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.
Synthesis and Mesomorphic Properties of New Chiral Liquid-Crystalline Diols
Molecular Crystals and Liquid Crystals, 2005
Two series of new ferroelectric liquid-crystalline diols with 1,3-propandiol group connected by a flexible spacer to the mesogenic part of the molecule have been synthesized. Both series are laterally substituted by methyl, methoxy, or chlorine substituents in the meta position to the carboxylic group of the 4-alkoxybenzoate unit. Phases and phase-transition temperatures were determined by polarizing microscopy and Differential Scanning Calorimetry (DSC). Mesomorphic properties of the studied compounds are compared and the effect of lateral substitution is evaluated. These new series of diols are predestined for preparation of liquidcrystalline polyurethanes by bulk polymerization in the temperature range of the SmC Ã phase.
Polymer, 2011
For the first time new type of liquid single crystal elastomers forming the chiral smectic A * (SmA * ) phase has been prepared using chiral lactic acid derivative as a co-monomer. The synthesis and the basic characterization of the ferroelectric liquid crystalline co-monomer based on differential scanning calorimetry and small/wide-angle X-ray scattering are reported and discussed. The monomer possesses the paraelectric SmA * and the ferroelectric SmC * phases over a broad temperature range. The preparation of new smectic liquid crystalline elastomers together with characterization of their mesomorphic and structural properties is also reported. New elastomers possess the orthogonal paraelectric SmA * phase over 50 K broad temperature range.
3-Hydroxycinnamic acid – a new central core for the design of bent-shaped liquid crystals
Journal of Materials Chemistry C, 2013
Structures of intermediates and final products were confirmed by 1 H NMR spectroscopy (Varian Gemini 300 HC instrument), deuteriochloroform was used as solvent and signals of the solvent served as internal standard, J values are given in Hz. Elemental analyses were carried out on a Perkin-Elmer 2400 instrument. Purity of all final compounds was confirmed by HPLC analysis (Tessek C18 25x4.5 RP column) and found >99.8%. Column chromatography was carried out using Merck Kieselgel 60 (60-100 m). The experimental part summarizes general synthetic procedures for the preparation of intermediates 1 and 3-5 and the target compounds of the series I, II and III. To a solution of 3-hydroxycinnamic acid (4.0 g; 24.4 mmol) and imidazole (3.4 g; 48.8 mmol) in dry DMF (45 ml), a solution of tert-butyl(dimethyl)silyl chloride in dry DMF (12 ml) was added dropwise. The reaction mixture was stirred at 60 °C for 9 h and then poured in cold aq. 1 M HCl (100 ml). The solution was extracted with ethyl acetate (3 75 ml), the combined organic solution was washed with aq. 6 M HCl (3 60 ml), water (2 60 ml) and dried with anhydrous magnesium sulphate. The solvent was evaporated and the crude product was crystallized from toluene to yield 5.3 g (78%) of acid 1, m.p. 114-117 °C. 1 H NMR (DMSO-
The Journal of Physical Chemistry B, 2010
We present a study on the effect of added CsCl and of temperature variation on the chiral induction in a chiral nematic lyotropic liquid crystal (LC) composed of the surfactant cesium perfluorooctanoate (CsPFO), water, and the chiral dopant D-Leucine (D-Leu). The chiral induction was measured as the helical pitch P. The role of the additives CsCl and D-Leu on the phase behavior is investigated and discussed. The thermal stabilization effect of CsCl is shown to lead to an apparent salt effect on the pitch when the pitch is compared at a constant temperature. This apparent effect is removed by comparing the pitch measured for different salt concentrations at a temperature relative to the phase-transition temperatures; thus, the real salt effect on the pitch is described. High salt concentrations are shown to increase the pitch, that is, hinder the chiral induction. The effect is discussed in terms of a decreased solubilization of the amphiphilic chiral solute D-Leu in the micelles due to the salt-induced screening of the surfactant head groups and the consequential denser packing of the surfactants. The temperature variation of the pitch is investigated for all CsCl concentrations and is found to be essentially independent of the salt concentration. The temperature variation is analyzed and discussed in the context of a theoretical model taking into account specific properties of lyotropic liquid crystals. A hyperbolic decrease of the pitch is found with increasing temperature, which is known, from thermotropic liquid crystals, to stem from pretransitional critical fluctuations close to the lamellar phase. However, the experimental data confirmed the theoretical prediction that, at high temperature, that is, far away from the transition into the lamellar phase, the pitch is characterized by a linear temperature dependence which is determined by a combination of steric and dispersion chiral interactions. The parameters of the theoretical expression for the pitch have been determined by fitting the experimental data. The analysis of the salt concentration dependence of these parameters indicates that the chiral induction mechanism of D-Leu is dominated by chiral steric interactions.