Investigations on photo and electrically switchable asymmetric bent-core liquid crystals

Abstract

New series of bent-core liquid crystals (8a–8d) synthesized and their photo and electrical switching properties were investigated. The homologous series of liquid crystals was constructed with five-ring system using structurally non-symmetrical rod-like mesogens connected with 1, 3-phenylene unit. The synthesized precursor and bent-core liquid crystals were characterized by FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. The mesophase characterization of the asymmetric bent-core liquid crystals was carried out using polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction studies. The significance of tail length (alkyl chain) and nature of mesogen was explored; shorter alkyl chains bent-core compounds exhibited non-switchable rectangular columnar B₁ phase. Whereas longer alkyl chain induces switchable lamellar B₂ phase, which was further confirmed by electro-optical methods. This lamellar B₂ phase exhibits antiferroelectric–anticlinic organization (SmC_AP_A) of the molecules in the layers. The photo-switching properties of bent-core azo molecules were investigated using UV–Vis spectroscopy, the trans to cis photoisomerization was observed at 30 s, whereas reverse processes take place in 40 s in chloroform.