Structural, optical and dynamical properties of a high birefringence laterally fluorinated terphenyl isothiocyanate

Abstract

A doubly fluorinated isothiocyanato butyl terphenyl compound exhibiting a broad range of the nematic and a narrow range of smectic phase has been investigated by X-ray, dielectric and optical methods and compared with the properties of singly and doubly fluorinated ethyl homologues to see the effect of fluorination and chain flexibility. Contrary to common perception, weak antiparallel correlation of molecules is observed in each compound both from X-ray and dielectric studies. Observed dielectric anisotropy is strong enough to ensure a driving voltage suitable for thin film transistor-based liquid crystal display. Measured splay elastic constant suggests that the present compound will exhibit the fastest response. Flip-flop mode relaxations are observed in a few hundred kHz to MHz range. All the compounds exhibit high birefringence (0.373–0.331). They also show high order parameters at low temperatures. These compounds are expected to be suitable for formulating high birefringence nematic mixtures for fast switching displays.

Keywords:

• high birefringence isothiocyanato terphenyls
• low driving voltage
• dipole–dipole correlation factor
• molecular association
• order parameter
• dielectric relaxation