A new series of liquid crystalline diblock copolymers composed of a polystyrene and a polymethacrylate with an azobenzene moiety in the side chain were synthesized through atom transfer radical polymerization and characterized by various techniques. Photoinduced birefringence of diblock copolymers and the azobenzene homopolymer was investigated and compared under different excitation conditions. The results show that the microdomain structures characteristic of diblock copolymers hinder the photoalignment of azobenzene mesogenic groups.

Dual‐mode switching of diffraction efficiencies, using either light or an electric field, is possible with a diffraction grating prepared from an azobenzene‐polymer‐stabilized liquid crystal. Light‐induced switching resulted from the cis–trans photoisomerization of the azobenzene unit, resulting in the nematic‐to‐isotropic phase transition of the liquid crystal (dark fringes in the Figure). This switching behavior is reversible and repeatable for many cycles.

Liquid crystalline (LC) ionomers containing azobenzene mesogens and three transition metal ions (Cu2+, Zn2+, and Mn2+) were prepared and characterized. Metal ions were found to exert significant effects on the photoinduced orientation of azobenzene mesogens and on the diffraction efficiency of holographic gratings. Using methacrylic acid for neutralization with metal ions, as compared with the copolymer with no metal, ionomers of Zn and Mn showed increased photoinduced birefringence and higher diffraction efficiency of birefringence gratings obtained by excitation with spatially modulated light polarization. By contrast, ionomers with Cu showed the opposite effects. As a whole, the behavior of photoinduced birefringence and holographic grating appears to be correlated with the thermal stability of the LC phase formed by azobenzene mesogens in the ionomer. Some new thoughts are discussed regarding the effect of metal and their ionic aggregates on the clearing temperature of LC ionomers. The interest for further exploring azobenzene LC ionomers is demonstrated by the finding that the insertion of a small amount of certain metal ions could be an effective means to improve or to tune the properties of azobenzene polymers.

No abstract