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, NO 2 , CH 3 ) and/or on the terminal rings (Cl, Br, CH 3 ) 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.

The effects of lateral halogen substituents on the low-temperature cybotactic nematic phase in oxadiazole based bent-core liquid crystals

“…on BCM have also been investigated. [5,13,26,27,[68][69][70][71][72][73][74] This is of interest because such groups will exaggerate the electrostatic profile (molecular dipole), and computational studies indicate that increasing the transverse dipole might stabilise the biaxial nematic phase (this idea has been investigated experimentally as well). [75][76][77][78] It has been demonstrated that subtle changes in the nature of the lateral groups can alter both the stability and types of liquid crystalline phases observed.…”

The influence of lateral substituents on the occurrence of a transition between two polar smectic phases with antiferroelectric properties

“…Introduction of substituents either in the central unit or in the arms of the BC also has significant effect on the nature of mesophase/s observed. The influence of lateral substituents at the central unit as well as at the outer rings of five-ring resorcinol derivatives [6][7][8] of seven series of compounds clearly demonstrates the effects. In order to examine the influence of larger substituents such as methoxy and ethyl groups, seven-ring compounds containing a biphenyl moiety have also been investigated.…”

Banana-calamitic Dimers: Further Variations of the Bent-core Mesogenic Unit

“…In contrast, novel phases can result, if the central phenyl ring is laterally substituted. Much more information is given in the reviews listed above [5][6][7][9][10][11]. This way, for example, the B 7 phase was at first found for derivatives of 2-nitroresorcinol [12] and the B 5 phase for 2-methylresorcinol esters [13].…”