Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.364, 889-898, 2001
Trans-1,2-difluorostilbenes: Promising materials for high dielectric biaxiality ferroelectric mixtures
A range of two- and three-ring liquid crystals have been synthesised that incorporate a trans-1,2-difluoroethene linking group. Some of the materials have surprisingly low melting points and high smectic C phase stability, and they exhibit the ideal phase sequence for ferroelectric hosts of smectic C to smectic A to nematic. The synthesis was accomplished in a convergent manner through the use of low-temperature lithiations to generate organometallics based on boron and tin. Palladium-catalysed cross-couplings and Michael-type reactions were used to generate the final mesogenic materials. The polar fluoro substituents enable the generation of ferroelectric mixtures with a high dielectric biaxiality which is very important in tauV minimum driving schemes. The alkenic linking group in stilbenes normally confers instability, but the difluoro-substituted analogues are stable compounds.