Synthesis and liquid crystalline properties of substituted 2,5‐diaryl 1,3,4‐oxadiazole derivatives without flexible chains

Abstract

A series of new compounds based on aromatically 2,5‐disubstituted 1,3,4‐oxadiazoles without flexible chains, formulated as p‐R–C₆H₄–(OC₂N₂)–(p‐C₆H₄)₂–R′ with (i) R = CH₃O, R′ = CH₃O, CH₃S, F, H (Ia–Id), (ii) R = CH₃S, R′ = CH₃O, CH₃S, F, H (IIa–IId) and (iii) R = F, R′ = CH₃O, CH₃S, F, H (IIIa–IIId) (p‐C₆H₄ and OC₂N₂ represent a p‐phenylene spacer and a 1,3,4‐oxadiazole ring, respectively), were synthesised and characterised by ¹H and ¹³C NMR, MS and HRMS techniques. Mesomorphic properties were investigated using differential scanning calorimetry and polarizing optical microscopy. All of the target compounds (except Id, IId, IIIc and IIId) exhibited an enantiotropic nematic mesophase with high melting temperatures. The liquid crystalline properties of these compounds were influenced greatly by polarity, steric factors and positions of the terminal groups. The effect of the terminal groups on the liquid crystal properties is discussed.

Keywords:

• 1,3,4‐oxadiazole derivative
• structure–property relationship
• synthesis

Acknowledgement

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