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Abstract A new series of photosensitive azo materials possessing a chiral alkyl lactate moiety and terminal n-alkyl carboxylate unit close to the azo group has been synthesized and studied. The length of the n-alkyl carboxylate chain has been systematically varied in order to establish the effect of the molecular structure on the self-assembling behaviour. Two series of materials possessing hexyl and dodecyl alkyl chains in the chiral part of the molecule have been studied. It has been shown that the length of both the alkyl chains strongly influences the mesomorphic behaviour, however, each chiral/achiral chain has different utility to tune the mesomorphic properties. With exception of the compound with the longest chains, all studied compounds exhibited the chiral tilted ferroelectric smectic C* phase. Based on the combination of terminal alkyl chains, chiral nematic, orthogonal smectic A*, and twist grain boundary smectic A* phases have been detected on cooling beyond the SmC* phase. The presence of the photosensitive functional N=N group in the molecular core allowed further tuning of the material properties by UV light illumination. The E -to- Z photoisomerization of the azo group and subsequent thermal back-isomerisation have been studied in solution by nuclear magnetic resonance and most importantly in the mesophases on bulk samples. We report on UV-induced isothermal switching from chiral smectic and nematic mesophases into the isotropic phase, respectively, and differences in the textures of mesophase upon restoration of the ordered liquid. Highlights • Photosensitive chiral liquid crystals exhibiting a broad SmC* phase as well as SmA*, TGBA* and N* phases are presented. • Low-energy UV light induces isothermal phase transition from SmC* over TGBA* (SmA*) and N* phases into the isotropic phase. • Fast isothermal transition from any mesophase to isotropic phase is enabled by high-energy UV light. [ABSTRACT FROM AUTHOR]

Photosensitive liquid crystals represent an important class of functional materials that experience rapid development. Hereby, we present novel bent-core liquid crystals bearing a lateral substitution on the central core and in the vicinity of the photosensitive unit—an azo group. The azo group enables fast (E)-to-(Z)-isomerization upon irradiation with UV-light and visible light, while the substitution facilitates the high stability of the photochemically formed (Z)-isomer. The effectiveness of the irradiation and the composition of photostationary states was determined by UV/Vis and 1H NMR spectroscopy. A nematic phase formed by the materials was characterized by differential scanning calorimetry and optical polarizing microscopy. We show that the materials easily change their relative configuration of the N=N double bond not only in solution, but also in the mesophase, which leads to fast isothermal phase transition from the nematic phase to isotropic liquid. [ABSTRACT FROM AUTHOR]

One of the most frequently utilized liquid crystalline (LC) materials is a rod-like (calamitic) compound 4-cyano-4′-pentylbiphenyl (5-CB). The main objective of this work is to enhance its functionality by introducing a photoresponsive diazenyl spacer in the aromatic core and replace the non-chiral pentyl chain with various chiral alkyl carboxylate units. The mesomorphic properties of the prepared materials have been studied using polarizing optical microscopy and differential scanning calorimetry. It has been found that materials with an extended aromatic system possess the liquid crystalline behavior. The studied LC materials have shown mesophases at lower temperatures than previously reported analogous substances. Furthermore, one of them exhibits a chiral orthogonal frustrated twist grain boundary smectic phase, which has not been previously observed for this structural type of materials. We also investigated photoresponse of the mesophases under illumination with UV-light (365 nm) using a polarizing optical microscope. A non-conventional photoresponse of the prepared materials in a crystalline phase is presented and discussed. [ABSTRACT FROM AUTHOR]

We present two isomeric series of photosensitive bent-core liquid crystals possessing a lateral chlorine atom in the central resorcinol unit and various linking units in the side arms. With the aim to tune properties of the nematic phase, we have varied the type of the linking unit in the lengthening arm with rising rigidity from benzoate ester, biphenyl, cinnamate, Schiff base to stilbene moieties. In addition to that, we have changed the position of the lateral substituent (chlorine) as well. The mesomorphic properties of the materials have been determined from differential scanning calorimetry, polarizing optical microscopy, dielectric spectroscopy and X-ray studies. We show that synergy of the linking unit with the effect of the lateral substituent gives rise to broad temperature range of mesophases — the nematic phase as well as a SmCP phase. Thanks to the presence of the photosensitive group in the molecular structure, we have been able to transform both mesophases to the isotropic phase under UV light. The chemical structure–mesomorphic properties relationships are discussed with the aid of ab initio calculations and the results presented in context with experimental data. • Two series of 4-chlororesorcinol-based photosensitive bent-core nematogens are presented. • Mutual position of chlorine atom on the central core and the azo group is crucial for mesomorphic behaviour. • Broad stable nematic phase below 100 °C and switchable SmC A P A phase are observed. • Photosensitivity of bulk mesophases is documented by X-ray profile and polarizing microscopy measurements. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]