Benzoxazole-based nematic liquid crystals containing ethynyl and two lateral fluorine atoms with large birefringence

New kinds of heterocyclic mesogenic compounds containing benzoxazole, ethynyl, and laterally fluorinated phenyl groups, namely 2-[4-[2-[4-alkoxyphenyl]ethynyl]-2,3-difluorophenyl]-benzoxazole derivatives (nPEDFPBx), are synthesized and evaluated. The compounds nPEDFPBx except nitro-substituted ones have enantiotropic nematic mesophases with mesophase ranges of 16–86°C and 29–108 °C on heating and cooling, respectively. The results show that introduction of two lateral fluorine atoms into molecule results in enhanced nematic mesophase stability. Meanwhile, nPEDFPBx displays much higher birefringence (0.507–0.624) than common tolane-based liquid crystals, which is ascribed to its large π-conjugated molecule composed of benzene, ethynyl, and benzoxazole mesogenic unit. The nPEDFPBx has a high potential to serve as a dopant for liquid crystal mixture.