The influence of lateral substituents on the mesophase behaviour of banana-shaped mesogens. Part II

Abstract

New materials are presented, derived from the original banana compounds where the first smectic phases with polar switching (SmCP) were detected. Our results demonstrate that the introduction of lateral substituents on the central ring (F, Cl, CN, NO₂, CH₃) and/or on the terminal rings (Cl, Br, CH₃) can significantly change the mesophase behaviour. The influence of such substituents is much more pronounced than in comparable calamitic compounds. The clearing temperatures are more or less depressed depending on the number, position and type of lateral substituents. In most cases the laterally substituted compounds form SmCP_A phases. Of basic and theoretical interest are compounds where substituents (e.g. 4-cyano; 4,6-dichloro) on the central core enhance the bending angle giving rise to polymorphism variants with conventional smectic and nematic phases as well as “banana phases”: N–SmCP_A; SmA–SmCP_A; SmA–SmC–SmCP_A; SmA–SmAP_A–SmCP_A. The last mentioned phase sequence has not been reported for single compounds up to now. Furthermore, the pool of materials allows us to compare the significant influence of lateral halogen atoms F, Cl, Br on the mesophase behaviour of bent-core mesogens for the first time. Nevertheless, up to now it has not been possible to predict the mesophase behaviour of bent core mesogens on the basis of the molecular architecture.