The synthesis and mesomorphic properties of 2,2′,3-tri- and 2,2′,3,3′-tetra-fluoro-1,1′∶4′,1″-terphenyls for high dielectric biaxiality ferroelectric liquid crystal mixtures

Abstract

Liquid crystalline 1,1′∶4′,1″-terphenyls with three and four lateral fluoro substituents and alkyl or alkoxy substituents in the 4- and 4′-positions have been synthesised. Synthetic strategies employed were convergent and involved the use of arylboronic acids and aryl halides in palladium-catalysed cross-coupling reactions. These syntheses are of particular interest because issues of selective metallation (at positions ortho to a fluoro substituent) and selective coupling reactions (bromo versus iodo sites) are involved, not all of which proceed as expected. All the trifluoroterphenyls and most of the tetrafluoroterphenyls generate the smectic C phase, the phase stability and temperature range of which were found to be highly dependent upon the relative lengths of the two terminal chains. The 2,2′,3- and 2,2′,3,3′-patterns of lateral fluoro substitution in 1,1′∶4′,1″-terphenyls generate materials of high lateral dipole and enable the formulation of ferroelectric mixtures with a high dielectric biaxiality which is very important in τV minimum driving schemes.