Synthesis and liquid crystalline property of H-shaped 1,3,4-thiadiazole dimers

Abstract

Two H-shaped liquid crystalline 1,3,4-thiadiazole dimers D₁ and D₂ and the corresponding monomers M₁ and M₂ were synthesised and characterised by ¹H/¹³C nuclear magnetic resonance (NMR) and high-resolution mass spectrometry. The thermal properties of the dimers and monomers were investigated by polarised optical microscopy, differential scanning calorimetry and thermogravimetric analysis. All of these compounds exhibited liquid crystalline behaviours with excellent thermal stabilities. The dimers displayed an enantiotropic or a monotropic nematic phase, while the monomers showed nematic and/or smectic A phases enantiotropically. The nature of the mesophases was determined by the molecular shapes and the terminal groups. Notably, the H-shaped dimers exhibited much lower clearing temperatures than the corresponding rod-like monomers.

Keywords:

• H-dimer
• 1,3,4-thiadiazole
• phase transition
• synthesis