The synthesis and mesomorphic behaviour of tetracatenar and hexacatenar bi‐1,3,4‐oxadiazole derivatives

Abstract

Symmetrical four‐chained (tetracatenar) and six‐chained (hexacatenar) bi‐1,3,4‐oxadiazole ester derivatives, namely 5,5′‐bis[phenyl(3,4‐dialkoxybenzoate)]‐2,2′‐bi‐1,3,4‐oxadiazole (Cn, n = 6, 10, 12, 14, 16) and 5,5′‐bis[phenyl(3,4,5‐trialkoxybenzoate)]‐2,2′‐bi‐1,3,4‐oxadiazole (Dn, n = 7, 10, 14, 16) were synthesised. The liquid crystalline properties were investigated by differential scanning calorimetry, polarised optical microscopy and wide angle X‐ray diffraction. It was revealed that the hexacatenar derivatives (Dn) are non‐mesomorphic, while the tetracatenar ones (Cn) showed a classic progression from smectic C phases (for C6 and C10) to a hexagonal columnar (Col_h) phase (for C12, C14 and C16) with the increase in length of the terminal chains. Molecules of Cn (n = 6, 10) tilt about 55‐56° from the layer normal within their SmC phase.

Keywords:

• bi‐1,3,4‐oxadiazole derivatives
• high‐angle tilting
• biforked mesogens
• hexagonal columnar phase

Acknowledgements

The authors are grateful to the National Science Foundation Committee of China (project No. 50373016), Program for New Century Excellent Talents in Universities of China Ministry of Education, Special Foundation for PhD Program in Universities of China Ministry of Education (Project No. 20050183057) and Project 985‐Automotive Engineering of Jilin University for their financial support of this work.