Synthesis and phase transition behaviours of new non-symmetric liquid crystal dimers

Abstract

A new series of non-symmetric liquid crystal dimers N-(4-(n-(4-(benzothiazol-2-yl)phenoxy)alkyloxy)-4-nitro-benzylideneimine) containing benzothiazole and benzylideneaniline as the mesogenic core units connected by a flexible alkyl spacer, -(CH₂)_n-, with n ranging from 2 to 6, 8, 10 and 12 have been prepared. Their molecular structures were proposed via spectroscopic techniques. Mesomorphic properties were studied using differential scanning calorimetry and polarising optical microscopy. The results showed that the clearing temperatures decreased upon lengthening of the alkyl spacers. Whilst even member with the shortest alkyl spacer (n = 2) exhibited nematic phase, the rest of even members (n = 4, 6, 8, 10 and 12) possessed smectic and nematic properties. Nematic phase range gradually decreased from n = 2 to n = 12. Odd members are belonged to non-mesogenic compounds except for n = 5 which exhibited monotropic (metastable) nematic phase.

Keywords:

• liquid crystal dimer
• benzothiazole
• benzylideneaniline
• smectic
• nematic

Acknowledgements

The authors would like to thank Ministry of Higher Education of Malaysia and Universiti Tunku Abdul Rahman for the financial supports via LRGS [No. LR003-2011A] and research facilities.