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

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.