Photoresponsive diblock copolymers bearing strong push–pull azo chromophores and mesogenic biphenyl groups

A series of diblock copolymers bearing strong push–pull azo chromophores and mesogenic biphenyl groups in the respective blocks was synthesized by reversible addition fragmentation chain transfer polymerization through two successive polymerization steps. All the diblock copolymers with different ratios of the block lengths exhibited photoinduced birefringence behavior similar to a corresponding azo homopolymer. After switching off the irradiation light, the birefringence relaxation of the diblock copolymers was found to be much smaller compared with that of the azo homopolymer, which is a very attractive advantage for photo-storage applications. On the other hand, the surface-relief-grating formation observable for azo homopolymer could not be detected for the diblock copolymers. The results indicate that the photoresponsive properties of the azo polymer block are closely related with the phase-separated structure of the diblock copolymers and can be further optimized to meet the requirement for specific applications.

► We synthesize a new type of liquid crystalline diblock azo copolymers.
► The liquid crystalline/isotropic diblock copolymers form phase-separated structure.
► The liquid crystalline blocks exist in the cybotactic nematic mesophase.
► All the block copolymers show the photoinduced birefringence.
► The birefringence decay is much smaller than that of corresponding homopolymer.