Photoinduced alignment of polymer liquid crystals containing azobenzene moieties in the side chain. 5. Effect of the azo contents on alignment behavior and enhanced response

A series of side-chain polymer liquid crystals (PLCs) of 6-[4-(4-ethylphenyl)diazenylphenyloxy]hexyl methacrylate and 4'-[6-(methacryloyloxy)hexyloxy]-4-cyanobiphenyl were synthesized and characterized. The effects of contents of the azo units and the wavelength of irradiation light on photoinduced alignment behavior were investigated. On irradiation of linearly polarized light (LPL) at 366 nm directly, alignment change was induced only in the PLC with 6 mol % azo units (P6), while phase transition took place in the other PLCs with higher contents of the azo units. On irradiation of LPL at 436 nm directly, alignment was induced with a fair efficiency in P15 and P35, low efficient alignment was observed in P6 and P100, and no alignment change was induced in P55 and P75, which exhibited a homeotropic state. A high alignment efficiency was achieved in all PLCs by using another method: irradiation with 366 nm unpolarized light at first and then with 436 nm LPL. The alignment change induced by this method was explored at various temperatures. All-optic switching might be realized by irradiation of 336 nm unpolarized light and 436 nm LPL alternatively based on the photochemical phase transition and the photoinduced alignment processes of the PLCs, respectively.