Synthesis and mesomorphic properties of different liquid crystal methacrylic azo monomers with ‘de Vries’-like behaviour

Abstract

The synthesis and characterisation of four azo aromatic monomers, possessing two aliphatic tails, one with a methacrylate group and six methylenic units, and the other oxyhexyl or oxydodecyl, was carried out. The aliphatic tails are attached to an aromatic system consisting of two phenyl rings linked through an azo group. Two of then possess a free hydroxyl group in one of the phenyl rings. The materials were characterised by polarised light microscopy, differential thermal analysis and X-ray diffraction. In the cooling cycle, M6OA8 exhibits a smectic A (SmA) phase throughout the liquid crystalline range, whereas M6A12 develops SmA and SmC mesophases; other monomers show a phase transition from SmA to a ‘de Vries’-like phase. The photoisomerisation of the chromophores was studied in solution by irradiation at different wavelengths.

Keywords:

• azo aromatic monomers
• de Vries phase
• photoisomerisation

Acknowledgements

C.M. González-Henríquez acknowledges a Scholarship from Conicyt and E.A. Soto-Bustamante is grateful for financial support from Project FONDECYT 2007 Nr. 1071059 and Merck Chile S.A.