Microwave-assisted synthesis and liquid crystal properties of 1,3,4-thiadiazole-based liquid crystals

Abstract

A series of 2-(4-alkoxyphenyl)-5-p-tolyl-1,3,4-thiadiazole derivatives 2a–2h were synthesised efficiently under microwave irradiation and solvent-free conditions. The thermal properties were determined using polarised optical microscopy (POM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). All these compounds exhibited enantiotropic liquid crystal properties with wide mesomorphic temperature ranges and good thermal stability. Compounds 2a–2f with short alkoxy chain (n = 1–6) all exhibited an enantiotropic nematic mesophase, while both nematic and smectic C mesophases were observed in compounds 2g (n = 7) and 2h (n = 8) with longer alkoxy spacer. The effect of the length of the alkoxy chain on liquid crystal properties is discussed in this paper.

Keywords:

• microwave-assisted synthesis
• 1,3,4-thiadiazole
• odd–even effect
• liquid crystals

Acknowledgements

This work was financially supported by grants from the National Natural Science Foundation of China (Project No. 20772064).