The synthesis of 1,4-disubstituted bicyclo[2.2.2]octanes exhibiting wide-range, enantiotropic nematic phases

Abstract

The 1,4-disubstituted bicyclo[2.2.2]octane ring has been incorporated in certain cyano-substituted systems to produce series of mesogens exhibiting wide-range nematic phases. 1-(4-Cyanophenyl)- and 1-(4′-cyanobiphenyl-4-yl)-4-n-alkylbicyclo[2.2.2]octanes are colourless stable materials, whose nematic phases are of low birefringence and of positive dielectric anisotropy. This combination of properties renders eutectic mixtures of these materials attractive for electro-optical display devices, especially those involving the cholesteric–nematic phase change mode. The liquid crystal transition temperatures of these mesogens are higher than those of analogous mesogens embodying a 1,4-disubstituted benzene ring or a trans-1,4-disubstituted cyclohexane ring in place of the 1,4-disubstituted bicyclo[2.2.2]octane ring. The compounds therefore demonstrate the capacity of the bicyclo[2.2.2]octane ring to give rise to interesting nematic materials.