Novel star-shaped liquid crystal macromolecules based on conjugated structures of azo and Schiff bases: synthesis and properties

Abstract

ABSTRACT In this paper, a series of novel liquid crystal units (ASE-n, n = 4, 6, 8) of azo Schiff bases with sulphonic acid (-SO3H) as terminal substituents and different alkyl chain lengths were designed and synthesised. Nine star-shaped liquid crystal macromolecules with different central groups (ASE-P-n, ASE-T-n, ASE-G-n, n = 4, 6, 8) were synthesised by esterification of three novel azo Schiff base liquid crystal units (ASE-n, n = 4, 6, 8) with phloroglucinol, pentaerythritol and glucose. The structure of the synthesised compounds were analysed by infrared spectroscopy and 1H NMR. The results showed that all the compounds were consistent with the molecular structure design. The properties of liquid crystal such as phase transition temperature and liquid crystal mesophase range were characterised by POM and DSC. The effects of alkyl chain length and branched degree on the properties of liquid crystal were studied. The maximum absorption spectrum of the compound was determined by UV-Vis spectrophotometry. The photoisomerisation reaction of the compound was also studied. Under ultraviolet light (λ = 365 nm) irradiation, the effect of different duration on the cis-absorption percentage of azo (-N=N-) bond in the compound was studied.