New ionic liquid crystals based on azobenzene moiety with two symmetric imidazolium ion group substituents

Imidazolium-substituted azobenzene liquid crystal derivatives were synthesised and their chemical structures were determined by 1H NMR, 13C NMR and UV spectroscopy and elemental analysis. The liquid crystalline properties pf the new compounds were investigated by differential scanning calorimetry, polarising optical microscopy and powder X-ray diffraction. The monomer DC10 was found to exhibit a monolayer smectic C (SmC) phase with schlieren texture on both heating and cooling. The effects of ionic interactions as well as the length of the alkyl chains on the mesophase are discussed. The results indicate that ionic interactions between imidazolium groups are the driving force for the formation of the monolayer SmC phase, the thermal stability of which is enhanced.