Novel benzoxazole-based liquid crystals with negative dielectric anisotropy and moderate optical anisotropy

A series of new liquid crystal compounds with negative dielectric anisotropy was synthesised by regulating the orientation of the substituents on the benzoxazole ring, namely, 5–4-(2-(4-(alkoxy)phenyl)-2,3-difluorophenyl)benzo[d]oxazole derivatives (nPP(2,3)FO). These compounds mainly display enantiotropic nematic mesophases in the ranges of 8.62–16.09°C (heating process) and 23.98–30.32°C (cooling process), moderate birefringence (Δn) ranging from 0.25–0.32 (DFT theoretical calculation) and 0.22–0.28 (experimental measurement), as well as negative dielectric anisotropy (Δɛ) ranging from −2.77 to −2.94. These characterises are ascribed to the larger perpendicular dipole moments and orientation angles of benzoxazole. This work provides new ideas for the rational design of negative dielectric anisotropy liquid crystals.