Non-symmetrical liquid crystal dimers armed with azobenzene and 1,2,3-triazole-cholesterol

Abstract

New non-symmetrical dimers which contain respective side units of azobenzene and 1,2,3-triazole-choloesteral have been synthesised from the reaction between 6-azido-[4-(4-acetylphenylazo)phenoxy]alkane and cholesteryl-4-(prop-2-ynyloxy)benzoate. The results show that the derivatives of 6-bromo[4-(4-acetylphenylazo)phenoxy]alkanes which possess the odd alkyl spacers exhibit dimesomorphism of N and SmA phases whilst the members with even numbers are non-mesogenic. However, the 6-azido-[4-(4-acetylphenylazo)phenoxy]-alkanes show N and SmA phases in a wide temperature range. On heating and cooling the target compounds cholesteryl 4-[(1-(6-(4-(4ʹ-acetylphenylazo)phenoxy)alkyl)-1H-1,2,3-triazol-4-yl)methoxy]benzoate show chiral nematic (oily streak and fan-shaped texture) and focal conic texture characteristics of smectic A phases with high thermal stability. Present investigation also reveals the effect of the spacer length upon the phase transition temperature. Intercalated arrangement is favoured by the molecules in the smectic phase. The observation is well established by XRD measurement wherein the actual molecular length is smaller than the theoretical value.

Keywords:

• non-symmetrical liquid crystals
• azobenzene
• 1,2,3-triazole-cholesterol
• smectic
• chiral nematic

Additional information

Funding

The main author (G.Y. Yeap) would like to thank Universiti Sains Malaysia for providing the research facilities and financial support under RU Research Grant [1001/PKIMIA/811159]. Authors are also grateful to the Malaysian Ministry of Education for the acquisition of some specialty chemicals purchased under the FRGS Grant [203/PKIMIA/6711265].