The first examples of V-shaped compounds exhibiting a B5 mesophase and a direct transition from the isotropic to a polar biaxial smectic A mesophase

Abstract

Here we report, the first observation of a B5 mesophase and a direct transition of the isotropic phase to a polar biaxial smectic A (SmAPA) mesophase in V-shaped compounds with acute angle. Achiral non-linear mesogens based on 1,2- (V-shaped) and 1,3- (bent-core) central phenyl rings are synthesised and characterized to investigate, the effect of different lateral substituents (X=H, Cl, F) on one of the wings and the bend angle at the centre of the molecule, on the liquid crystalline properties. The mesomorphic properties of these compounds are investigated using polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical measurements. It is found that V-shaped compounds form orthogonal smectic mesophases, viz., SmAPA and B5, whereas, bent-core compounds form a tilted smectic mesophase viz., B2 (SmCAPA). The lateral substituents affected the liquid crystalline properties in the case of V-shaped compounds, while they had not much effect on the mesogenic properties of bent-core compounds. The compounds forming orthogonal polar smectic mesophases, such as, SmAPA and B5 are of technological importance.