Benzoxazole-terminated liquid crystals with high birefringence and large dielectric anisotropy

Six benzoxazole-terminated mesogenic compounds with fluoro substituent at different positions were prepared and their properties investigated. The compounds give a high birefringence (Δn~ 0.45) and a large-dielectric anisotropy (Δε~ 26), indicating a possible application in liquid-crystal mixture as a dopant to enhance performance of the host mixture. In accordance with conventional high Δn liquid crystals containing triple carbon-carbon bonds, lateral fluoro substituents and terminal groups can alter the Δn and Δε of benzoxazole-terminated liquid crystals. Meanwhile, some parameters such as dipole moment, polarisability, dihedral angles are calculated with density functional theory (DFT) methods to relate to the experimental Δn and Δε. It is noted that the introduction of the benzoxazole unit is an effective method to enhance Δn and Δε values of the rodlike molecule, this is ascribed to its π-conjugated benzene-fused heterocycle and large dipole moment.