Abstract
We present the synthesis and mesomorphic properties of the new series of bent-core liquid crystals based on 3-hydroxybenzoic acid bearing a lateral substituent in the apex position. Four different substituents of various sizes and electronic properties have been used. We have found that only compounds substituted with fluorine are mesogenic and exhibit one mesophase, whose type differs when prolonging the terminal alkyl chain. For homologues with shorter alkyl chains (octyl, decyl), a columnar B1-type of a mesophase was observed, while materials with longer terminal chains (dodecyl, tetradecyl) exhibited a switchable lamellar SmCAPA phase. Calorimetric measurements, texture observations under a polarizing microscope were performed and electro-optical properties studied. Additionally, dielectric measurements were realized to characterize the molecular dynamics in the SmCAPA phase. All mesogenic compounds were further studied by X-ray measurements to confirm phase identification and obtain more information about their structural parameters.
Highlights
Bent-core materials represent a unique class of liquid crystals (LCs)
All compounds were studied by a calorimetric method; Differential scanning calorimetry (DSC) measurements were performed at the heating and cooling runs
The transition peaks observed in DSC plots were sharp and revealed big enthalpy values associated with phase transitions, for demonstration see Figure 1 with thermographs for two selected compounds from the series I
Summary
Bent-core materials represent a unique class of liquid crystals (LCs). The first compounds of this type were already synthesized at the beginning of the 20th century [1] They were not studied more widely due to the low thermal stability of formed mesophases. They were rediscovered in the 1990s, when the polar character and macroscopic chirality of mesophases formed exclusively by bent-core materials were described [2,3]. Bent-core compounds can form a broad variety of mesophases ranging from low-organized nematic phases over various lamellar mesophases to structurally complex ones [4]. The polar and chiral orders of nematic phases formed by bent-core LCs are nowadays of great interest [8,9,10]
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