Unconventional Behaviour of Asymmetric Bent-Core Mesogens: Chemical and Physical Aspects

Abstract

Bent-core liquid crystals (BLCs) have taken centre stage in current LC science as they exhibit distinct mesophases with fundamentally new properties. The observation of polar order and chiral superstructures in the mesophases of achiral bent-core molecules has led to “banana mania”. BLCs generally promote ordered molecular organizations and exhibit chiral and polar banana or smectic (Sm) phases. However, the nematic phases of bent-core mesogens are infrequent but could be induced by modifications in the molecular architecture. The fascinating bent-core nematics (BCNs) show technologically significant phase structures such as cybotactic clustering, ferronematic phase, heliconical structure/nematic twist-bend, etc. The unprecedented electrical, optical, and mechanical responses render BCNs as potential candidates for new and improved applications involving diffraction gratings, optical storage devices, and electro-optical displays. This presentation describes the rational design and synthesis of five new series of asymmetric bent-core mesogens exhibiting unconventional properties. The first series shows low- temperature nematic and orthogonal smectic phases in three-ring-based bent-core molecules. The bent-core molecular architecture with a stable antiparallel arrangement is established in these compounds. 1 The second series describes an extensive study of the impact of terminal halogens on the molecular self-assembly of hockey-stick-shaped mesogens. 2 The third series presents a disparity in the structural organization of polar and non-polar bent-core molecules exhibiting long-range nematic phase. 3 The fourth series is an example of “de Vries-like” LCs where an unprecedented low-layer shrinkage from SmA-SmC phase transition is observed in achiral unsymmetrical bent-core compounds with terminal alkoxy chains. 4 The last series shows ferroelectric-like switching and electric-field induced Fréedericksz transitions (FT) in the cybotactic nematic phase of polar unsymmetrical bent-core molecules. The FT mechanism is shown to be the precondition for producing patterns that are relevant for applications in optical instruments. 5 The distinctive properties for the technological prospect are highlighted in the presentation. 6,7 ___________________________________________________________________________ 1 New J. Chem. 2017, 41, 5403-5411. 2 Mol. Syst. Des. Eng. 2018, 3, 839-852. 3 J. Mol. Liq. 2019, 295, 111687. 4 Chem. Sci. 2022, 13, 2249-2257. 5 Manuscript 10.1080/02678292.2022.2028313 submitted. 6 ChemPhysChem 2021, 22, 1361-1370. 7 Liq. Cryst. 2022, DOI: