Photoinduced birefringence of novel azobenzene poly(esterimide)s; the effect of chromophore substituent and excitation conditions

• Photosensitive and processable poly(esterimide)s with azobenzene moieties were synthesized.
• The effect of substituent and excitation conditions on photoinduced birefringence was studied.
• High level of birefringence (0.023) for polymers with –CH3 and –OH substituent was found.
• A relatively low relaxation rate for the polymer with –CH3 substituent was observed.

This paper describes novel poly(esterimide)s containing azobenzene moieties, interesting from the point of view of potential applications in photonics. The polymers were prepared by polycondensation of 2,2′-[N-phenylethyloaniline-di(4-estro-1,2-dicarboxylic)]anhydride with azo-diamines bearing different substituents in the para position of azobenzene units. The light-induced birefringence of polymer films was measured under continuous-wave irradiation at 405 nm to determine the role of a chromophore substituent on the writing and relaxation behavior. Additionally, for the poly(esterimide) with the hydroxyl substituent the photoinduced birefringence was studied using the tunable pulsed irradiation. The results showed the largest birefringence for hydroxyl and methyl homologs and the lowest relaxation for the later material. The pulsed irradiation performed for the wavelengths located on the red side of azochromophore absorption band revealed a significantly more efficient birefringence generation under the excitation wavelength corresponding mainly to the n–π* trans azochromophore transition in comparison to the wavelength corresponding to the π–π* transition.