Fluorocarbon and Hydrocarbon N‐Heterocyclic (C5–C7) Difluorooxymethylene‐Bridged Liquid Crystals

A series of new fluorocarbon and hydrocarbon N-heterocyclic (C-5-C-7) difluorooxymethylene-bridged liquid crystals have been prepared. The impact of ring (C-5-C-7) as end group was investigated. Compounds with terminal N-heterocyclic 5- or 6-membered rings such as 3,4-difluoropyrrole, pyrrolidine, or pyridine, exhibited nematic phases (N). Whereas the terminal 3,3,4,4-tetrafluoropyrrolidine and 3,3,4,4,5,5-hexafluoropiperidine derivatives exhibited smectic C and B phases; the mesomorphic behavior weakened with increasing ring size. These new compounds also exhibited promising physicochemical and electro-optical properties. Modification of the ring size with different length alkyl groups and variation of the chains from alkyl to polyfluoroalkyl markedly changed the properties of these compounds. It is possible that these N-heterocycles (C-5-C-7) could replace fluorobenzene as terminal groups to form valuable difluorooxymethylene-bridged liquid crystals. Compounds with 3,4-difluoropyrrole as terminal group showed strongly positive dielectric anisotropy (E), moderate birefringence (n), and relatively low viscosity ((1)), thus meeting the criterion for high-performance liquid-crystalline materials.