The Thermal Cis–Trans Isomerization of Azopolyimides in the Solid State

Azobenzene-containing polymers, also known as azopolymers, are a wide group of materials interesting from the point of view of their potential utilization in the fields of photonics, optoelectronics, and biology as cell culture substrates and biomaterials. They are utilized as thin films on the substrates or free-standing foils. This class of polymers contains light-sensitive linkages -N=N- in their chemical structure. Azobenzene derivatives occur in the form of two isomers: an energetically stable trans-isomer and a metastable cis-isomer. Under the irradiation of azochromophores with a specific wavelength, the reversible trans–cis–trans isomerization is observed. The stability of cis-isomer in the solid state is crucial in some azopolymers applications, which can be tailored by changing the azochromophore structure, kinds of azo-molecules incorporation to the polymer backbone (covalent or non-covalent), and polymer molar masses. The knowledge about the influence of mentioned factors supports designing azopolymers with desired properties adjusted to a particular device. This paper is devoted to showing the impact of azopolyimide structure (main chain, side chain or T-type polymers, and “guest–host” systems) on trans–cis and cis–trans isomerization process in the solid state based on literature review and investigations published in our previous works.