Trans−1,2-Difluorostilbenes: Promising Materials for High Dielectric Biaxiality Ferroelectric Mixtures

Abstract

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 τV minimum driving schemes. The alkenic linking group in stilbenes normally confers instability, but the difluoro-substituted analogues are stable compounds.

Key Words:

• liquid crystals
• synthesis
• smectic C
• ferroelectric