Synthesis and mesomorphic behaviour of heterocycle‐based liquid crystals containing 1,3,4‐oxadiazole/thiadiazole and thiophene units

Abstract

A new class of thiophene‐based 1,3,4‐oxadiazole derivatives ( n ‐OXD‐R) and the corresponding 1,3,4‐thiadiazole derivatives ( n ‐THD‐R) was synthesised and characterised by means of ¹H NMR, ¹³C NMR, MS and HRMS techniques. Liquid crystal properties were investigated by differential scanning calorimetry, polarising optical microscopy and variable temperature X‐ray diffraction measurements. All the 1,3,4‐thiadiazole compounds ( n ‐THD‐R) exhibited enantiotropic mesophases (smectic A, smectic C and nematic phases) with wide mesomorphic temperature ranges (68.5–109.5°C). In contrast, only the oxadiazole compounds 8‐OXD‐Cl, 9‐OXD‐Cl and 10‐OXD‐Cl, bearing electron‐withdrawing terminal group and longer alkoxy chain, displayed an enantiotropic smectic A phase with narrow mesomorphic temperature ranges (4.1–10.9°C). The effects of central heterocyclic rings, the terminal groups and the length of the terminal alkoxy on the mesomorphic behaviour are discussed.

Keywords:

• 1,3,4‐oxadiazole derivative
• 1,3,4‐thiadiazole derivative
• thiophene liquid crystals
• synthesis

Acknowledgements

This work was financially supported by grants from the National Natural Science Foundation of China (Project No. 20772064). We thank for Dr. Stephen Chui and Prof. Chi‐Ming Che (Department of Chemistry, The University of Hong Kong) for assistance in the VXRD measurements.