Synthesis and Mesomorphic Property of 2,5-Aryl-1,3,4-Oxadiazole/Thiadiazole Derivatives Bearing a Terminal Thiophene Unit

The synthesis and characterization of a series of heterocyclic compounds 2a-2d based on 1,3,4-oxadiazole/ thiadiazole, furan and thiophene units are reported. The thermal behaviors of these compounds were investigated by means of differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and thermogravimetric analysis (TGA). The 1,3,4-thiadiazole derivative 2b exhibited enantiotropic smectic C and A mesophases with wide temperature range and good thermal stability, while all of the other compounds did not show liquid crystalline behaviors. The results indicate that 1,3,4-thiadiazole-based compounds are more beneficial to form stable mesophases than the corresponding 1,3,4-oxadiazole analogues, and the compounds with a central furan unit as the rigid core may result in the loss of the meosgenic behaviors due to the non-linear molecular structure.