Abstract
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.
Highlights
Liquid crystals (LCs) represent one of the most prominent classes of materials of today’s information age
We focused on the evaluation of optical purity of lactic acid-based building blocks used for the synthesis of a broad range of chiral liquid crystals (CLCs)
We have shown that frequently utilised synthetic procedures do not afford enantiomerically pure building blocks
Summary
Liquid crystals (LCs) represent one of the most prominent classes of materials of today’s information age. The molecules of LCs can self-assemble into organised supramolecular structures (mesophases) that combine the fluidity of liquids with the long-range order of solids [1,2]. Molecules in a mesophase readily respond to external stimuli such as electric and magnetic field, light and mechanical stress. Thanks to these properties, LCs have found many applications, for example, in liquid crystal displays (LCDs), optical shutters, light beam steering and shaping [3,4]. Among LCs, chiral liquid crystals (CLCs) represent an important class of materials that can self-assemble into chiral mesophases [5]. Macroscopic chirality of the mesophases results in special properties, such as (anti)ferroelectricity, selective reflection of light, and heat sensitivity, which render
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