Microphasic separation-induced enantiotropic liquid crystal behaviour single phenyl unit series based on the fluorophobic effect

Abstract

The aim of this work was to demonstrate the possibility of obtaining enantiotropic liquid crystals containing a single phenyl group over a wide temperature range but without hydrogen bonding. We report the synthesis and characterization of several alkoxy monophenyl compounds linked by a thioester group to a 2-(perfluoro-n alkyl) ethyl chain. Compared with previous work using monophenyl cores, the synthetic pathway provides compounds is high yields from cheaper raw materials, i.e. 4-hydroxybenzoic acid. The mesomorphic properties were characterized using polarized light microscopy and differential scanning calorimetry. The effects of lengthening the substituents on the phenyl core were considered: varying the length of the alkyloxy groups had a marked effect, with the formation of enantiotropic mesomorphic phases with a maximum temperature range of 70°C. The temperature range of the mesomorphic phase is inversely proportional to the length of the alkyl chain and exhibits an odd-even effect. Decreasing the fluorinated chain length leads to a regular decrease in both the melting and clearing temperatures, giving room temperature transitions. This design approach using a single ring as the mesogenic core is of great interest in the development of low cost LC materials based on the fluorophobic effect.