Synthesis and chiroptical properties of liquid crystalline copolymers containing azobenzene chromophores

A series of new liquid crystalline copolymers, poly[((S)-2-methyl-1-butyl methacrylate)-co-(6-(4-(4-cyanophenylazo)phenoxy)hexyl methacrylate)], with different contents of chiral units of 17, 36, 54 and 78mol% were synthesized. The structures and properties of the copolymers were characterized and evaluated using infrared, H-1 NMR and UV spectroscopy, differential scanning calorimetry, gel permeation chromatography and circular dichroism (CD). The CD results suggested that absorptions of azobenzene chromophores were observed in films of copolymer containing 17, 36 or 54mol% chiral units, but not in. the film of copolymer containing 78mol% chiral units. Also, CD values of the copolymeric films decreased with increasing chiral content. After irradiation with linear polarized light at 442 nm, CD values were changed in all the copolymeric films, and the CD values increased with decreasing chiral content in a nonlinear way, while the photoinduced change of chirality of the copolymers increased in a linear way with decreasing chiral content. The results are discussed in terms of interactions between structures and chiroptical properties. (c) 2007 Society of Chemical Industry