Mirror symmetry breaking in fluorinated bent-core mesogens

Abstract

Spontaneous chirality synchronization in the LC phases of achiral bent-core molecules, the so called dark conglomerate mesophases (DC^[*] phases), is a challenging task with significant importance for fundamental scientific research and potential applications. Here we report the synthesis and investigation of two new series of achiral bent-core mesogens derived from 4-bromoresorcinol and 4-chlororesorcinol with 2,3-difluorinated azobenzene-based side arms. The self-assembly of these materials was characterized by DSC, polarizing microscopy, X-ray diffraction investigations (XRD) and electro-optical studies. Depending on the type of halogen substituent at the central resorcinol core and on the terminal alkyl chain length different types of mesophases were observed, where 4-bromoresocinol derived compounds predominately show helical nanocrystallite phases, (HNC phases), representing conglomerates of chiral domains (DC^[*]), whereas the related 4-chlororesorcinol based compounds form smectic C phases with a polar domain structure (SmC_sP_AR). Comparison with related compounds provides information about the influence of core fluorination on the mesophase behaviour and DC^[*] phase formation, thus providing a step forward in uncovering the molecular design principles of LC materials capable of mirror symmetry breaking.