Photo-induced birefringence and all-optical switching effect in azobenzene-grafted polyurethanes

Abstract In this study, azobenzene-containing chromophore 4- N , N ′-bis-(2-hydroxyethyl)amino-4′-nitro-azobenzene were synthesized by using 4-nitroaniline and m -tolyldiethanoamine. Then they were polymerized with toluene 2,4-di-isocyanate (TDI) and polyethylene glycol (PEG) in N , N ′-dimethylformamide (DMF) to obtain novel polyurethanes which exhibit photo-induced birefringence properties. Polyols such as 1,4-dibutanol or tri-hydroxyl propane were introduced into the polyurethane structure to adjust the flexibility of the polymer chain segments. An experimental setup, in which the He–Ne lasers produced signal beams and Ar + lasers the pump beams, was employed to investigate the photo-induced birefringence and optic–optic switching properties of these polyurethane materials. It is found that, with increasing pump beam power, the extent of both birefringence and optic switching response first slightly increased due to reorientation mechanism, and then decreased due to thermal effects. And the flexibility for the chain segment also has remarkable effects on birefringence extents and optic switching modulations.