Design and synthesis of photoresponsive bent-core liquid crystals exhibiting polar smectic phases

Abstract

Bent-core liquid crystals represent a fascinating class of self-assembling materials. This is due to their unique organized fluidic states – mesophases – that are widely studied for their electro-optical and photonic responses. We designed and synthesized two series of mesogens based on laterally substituted 3-hydroxybenzoic acid, systematically tuning their properties by varying the linking group in both side arms. The mesomorphic behaviour was investigated using polarizing optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction, revealing the presence of several types of smectic phases. For homologues containing a photoresponsive azo group, we evaluated their light-induced switching in solution as well as in mesophase, under external UV irradiation. We demonstrated that these materials can completely undergo the light-induced switching from a mesophase to an isotropic liquid under in situ illumination during X-ray measurements. Unlike previously reported analogues with related structures, the studied compounds exhibited nematic phases with surprisingly narrow temperature range and stable enantiotropic antiferroelectric polar smectic C phases. A transition from a polar SmC to SmC_AP_A phase is also documented.