The preparation and liquid crystal properties of materials incorporating a mono-substituted ring system

The liquid crystal properties of a homologous series from methyl to heptyl of novel I-(trans-4-alkylcyclohexyl)-2-phenylethanes (PECH) are presented. These compounds are stable materials of low viscosity and low dielectric anisotropy incorporating the -CH,CH,- inter-ring linkage. Comparisons are made between the propyl homologue, PECH 3.H, and the commercial isomeric material PCH 3.2. The effect of replacing the trans-cyclohexane ring with a bicyclo(2.2.2)octane ring is discussed. A reversed PECH system, in which the alkyl chain is attached to the aromatic moiety (mono-substituted cyclohexane ring), was prepared. An analogous mono-substituted cyclopentane system was also investigated. The separation of two polar/highly polarisable functions in a molecule by a non-polar, non-conjugated group is known to have a detrimental effect on the liquid crystal thermal stability. A collection of data exemplifies this effect which is discussed simply in terms of molecular bonding principles.