Novel chiral liquid crystals based on amides and azo compounds derived from 2‐amino‐1,3,4‐thiadiazoles: synthesis and mesomorphic properties

Abstract

Novel chiral amides (Ia–Ie, II) and azo compounds (III, IV) with a 1,3,4‐thiadiazole unit in the rigid core were synthesized and their liquid crystalline properties investigated by polarizing optical microscopy and differential scanning calorimetry. The amides Ia–Ie contain a chiral alkoxy chain derived from (R)‐2‐octanol and an achiral chain varying from 6 to 10 carbon atoms at the end of the rigid core. In amide II one of the terminal group is a chiral alkoxy chain derived from (S)‐isoleucine and the other terminal substituent is an achiral n‐decyloxy chain. Azo compounds III and IV contain an achiral n‐decyloxy chain and a chiral alkoxy chain derived from (R)‐2‐octanol and (S)‐isoleucine, respectively, at the end of the rigid core. The first homologue in the series of amides (Ia) exhibits enantiotropic smectic X (SmX)–chiral nematic (N*) dimorphism and the homologues Ib–Ie display enantiotropic SmX–chiral smectic C (SmC*)–N* mesomorphism. Amide II displays an enantiotropic smectic A phase. The azo compounds III and IV do not show smectic order and only an enantiotropic N* phase was observed. Thus, the mesomorphic behaviour depends on the nature of the central linkage and on the nature of the chiral alkoxy chain.

Acknowledgement

This work was supported by FONDECYT (Grant 1030696) and “Dirección de Investigación, Universidad de Concepción”.