Fast switching near a smectic‐to‐nematic phase transition

Abstract

We have designed, synthesised and evaluated the physical properties of high‐birefringence (Δn) isothiocyanato phenyl‐tolane and terphenyl liquid crystals. These compounds exhibit a Δn∼0.36–0.52 at room temperature and wavelength λ = 633 nm. A different mesomorphic sequence was observed depending on the terminal alkyl chain length. Compounds with a longer chain show smectic and nematic phases, whereas short‐chain homologues only exhibit a nematic phase. In the vicinity of the nematic‐to‐smectic transition, the viscoelastic coefficient decreases, instead of increases, as the temperature decreases. The observed change is as large as 75% for the 4′‐(3,5‐difluoro‐4‐isothiocyanatophenylethynyl)‐4‐pentylbiphenyl compound studied. This behaviour is useful for improving the response time of a liquid crystal device, if the operating temperature can be controlled accurately.