Influence of terminal groups on liquid-crystalline polymorphism of selected azobenzene derivatives

Abstract

This article describes the synthesis and liquid-crystalline characterisation of four kinds of azobenzene derivatives: 1-[4-(hexyloxy)phenyl]-2-(4-X-phenyl)diazenes (A), 4-[(4-X-phenyl)diazenyl]phenyl heptanoates (B), 4-[(4-X-phenyl)diazenyl]phenyl 4-(dodecyloxy)benzoates (C) and 4-[(4-X-phenyl)diazenyl]phenyl 4-{[(2S)-2-chloropropanoyl]oxy}benzoates (D), where X is the alkyl, alkyloxy alkylcarbonyl and alkyloxycarbonyl substituents. Among the 32 calamitic mesogens presented (13 of them are described here for the first time), the following mesophases were observed: nematic, SmA, SmC, B_hex, B_Cr and G. About half of the investigated compounds exhibit more than one mesophase. We noted and compared the relationship between the type of the substituent and the type of liquid-crystalline phases and their temperature ranges.

Keywords:

• liquid crystals
• terminal groups
• azobenzene
• nematic
• smectic