Synthesis and characterisation of novel imidazolium‐based ionic liquid crystals with a p‐nitroazobenzene moiety

Abstract

A novel series of compounds with different counter anions, i.e. 1‐{[4‐(4‐nitrophenylazo)phenyloxy]}alkyl‐3‐methyl‐1H‐imidazol‐3‐ium bromide salts (C_n , n = 3, 6, 10) and tetrafluoroborate salts (D_n , n = 3, 6, 10), were synthesised by the incorporation of an imidazolium group into paraffin side chain‐terminated 4‐nitroazobenzene derivatives. Their chemical structures were determined by ¹H NMR, ¹³C NMR, UV spectroscopy and elemental analysis. The thermotropic liquid crystalline properties of these materials were further studied by polarising optical microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry. The results show that C_n and D_n (n = 6, 10) exhibit smectic liquid crystalline phases. The ionic liquid groups play an important role in forming the smectic layer structure, via enhancement of the thermal stability of the smectic state.

Keywords:

• ionic liquid crystals
• imidazolium derivatives
• smectic phase enhancement

Acknowledgements

The authors are most grateful to the National Science Foundation of China (No.20475053 and No.20673109), Department of Science and Technology of Jilin Province (No.20050102) and Ministry of Science and Technology of China (No.2006BAKB05).