Synthesis and evaluation of nematic 4-alkenyloxy- and 4-alkenoyloxy-4 '-cyanobiphenyls

There is a direct correlation between the physical properties of a nematic mixture utilised in TN- and STN-LCDs and display optical performance. Since it is known that the presence of a carbon-carbon double bond in nematic li quid crystals can influence some physical properties of nematics advantageo usly([1,2]), we have introduced a carbon-carbon double bond into the termin al chain of a variety of laterally and terminally substituted biphenyl deri vatives. The position and configuration of the double bond has been varied systematically and the optimal combination for nematic phase formation and low melting point identified. Homologous series of 4-(E)-alk-2-enyloxy-4'-c yanobiphenyls (ethers) and 4-(E)-alk-2-enyloyloxy-4'-cyanobiphenyls (esters ) have been synthesised. The esters exhibit higher nematic-to-isotropic tra nsition temperatures and wider temperature ranges of the nematic phase than the corresponding ethers. Some initial correlations have been established between the transition temperatures, viscosity, elastic constants, dipole m oments, birefringence, etc. and molecular structure.