Increasing the negative dielectric anisotropy of liquid crystals by fluorination of the terminal ethyl chain

Abstract

ABSTRACT Ten new negative dielectric anisotropy liquid crystal compounds with terminal 2-fluoroethyl group were synthesised and their structures were confirmed by 1H-nuclear magnetic resonance and mass spectra. Thermal analysis shows that the four compounds bearing two rings are non-mesogenic, and among the compounds bearing three rings, two compounds exhibit only nematic phase and the others exhibit both smectic and nematic phases. Compared with the terminal ethyl analogues, the introduction of fluorine leads to a significant increase in dielectric anisotropy and a slight decrease in the clearing point. Unexpectedly, the rotational viscosity also decreased significantly. Density functional theory (DFT) calculation results reveal that the gauche conformation of 2-fluoroethoxyl benzene has the lowest total energy and it is beneficial to the increase in polar moment, which eventually leads to a large increase in dielectric anisotropy.