Synthesis and characterisation of reactive liquid crystals containing an azo group

Abstract

A new series of liquid crystal (LC) monomers – not only contain a double bond but also contain an azo group – were designed and synthesised. The length of side groups in the LC monomers containing azobenzene ester varied from 1 to 2 methylene units, and the length of the substituted groups in the main chain varied from 1 to 3 methylene units. The molecular structures of the intermediates and target compounds were confirmed by Fourier transform infrared, ultraviolet and visible spectrum and nuclear magnetic resonance (NMR) spectroscopy. The thermal phase behaviour of the LC monomers was investigated by polar optical microscopy coupled with hot stage and differential scanning calorimetry (DSC). In this paper, the effect on the LC zone with the substituents were investigated, and with the increased methylene of main chain, the melting point and the phase transition temperature of the substance will be lowered and LC regions will be narrower.

Keywords:

• phase transition
• nematic
• reactive liquid crystal
• synthesis
• azo

Acknowledgements

We would like to thank Prof. Fan Xiaodong for the analysis of DSC and Dr. Liu Baojian for assistance in obtaining some of the NMR spectra and FT-IR spectra.