Balance the trade-offs between high birefringence, large dielectric anisotropy and low viscosity in nematic liquid crystals through molecular splicing strategy

Abstract

ABSTRACT A series of liquid crystals containing one n-propyl/n-propoxy, lateral fluorine substituent, a tolane mesophase unit, and a 2,2-difluorovinyl terminal group were designed and synthesised. Their chemical structures were characterised and confirmed by nuclear magnetic resonance (NMR), mass spectrometry and Fourier transform infrared spectrometry (FTIR) instruments. Meanwhile, the position and number effects of lateral fluorine substituents on the thermal, mesomorphic, and electro-optical properties of these compounds were explored. Furthermore, density functional theory (DFT) calculations of molecular conformation, polarisability components and dipole moment were utilised to correlate the experimental results. Research results show that the 2,2-difluorovinyl-terminated liquid crystal compounds possess excellent properties of low melting point, wide nematic-phase temperature interval, high birefringence, large dielectric anisotropy and low rotational viscosity. This molecular splicing strategy is an effective method to balance the trade-offs between high birefringence, large dielectric anisotropy, and low viscosity in nematic liquid crystals.