Effects of Polysubstitution on Mesomorphic Properties: Chloro Derivatives of 4-Methoxyphenyl 4-(Phenyliminomethyl)-benzoate and Related Compounds

Abstract

Abstract The effects of mono-, di-, and trichloro substitution of one of the end phenyl rings upon the nematicisotropic transition temperature have been studied employing seven three-ring systems with a terminal methoxyl group, in which the linkage groups are ‒;CO‒O‒ and ‒CH˭N‒. The transition temperatures in these compounds were mostly in this order; 4-Cl < 2,4-Cl2 < 2,3,4-Cl3 < 3,4-Cl2 < unsubstituted < 2.3-Cl2 < 2-Cl or 3-Cl. Both the substituents on the 2- and 3-positions drastically lowered the transition temperature of the parent compound and the extent of depression by the former substituent varied by a factor of more than two when the ‒CH˭N‒ group nearby was inverted. The condition that the thermal stabilities of mesophases and the temperature ranges over which the mesophases exist must be considerable in a parent compound was not necessarily required for the appearance of an enantiotropic nematic-isotropic transition in laterally substituted derivatives.