New Luminescent Liquid Crystals Based on 2,1,3-Benzothiadiazole and Bent Five-membered<i>N</i>-Heterocyclic Cores

Abstract

New fluorescent liquid crystalline (LC) compounds containing the 2,1,3-benzothiadiazole chromophore as the central core substituted with 1,2,4-oxadiazole, 1,2,3-triazole and 1,2-isoxazole heterocycles were synthesised and their mesophases characterised by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. We observed that the bent angles of the five-membered heterocyclic substituents are crucial in determining the thermal stability of the LC phases formed, indicating a delicate balance of forces involved in LC phases. The mesophases formed by all symmetrical and unsymmetrical compounds showed thermal stability in the order 1,2-isoxazole > 1,2,3-triazole > 1,2,4-oxadiazole.