Comprehensive investigations of trans-cis-trans isomerization in the solid state for azo polyimides

This work describes the thermal cis-trans isomerization in the solid-state for poly(ether imide)s and poly(ester imide)s with azobenzene or azo pyridine moieties. The cis-trans relaxation was monitored for covalently functionalized polyimides (main-chain, side-chain, "T-type") and "guest-host" azo systems. The obtained results from the investigations allow us to formulate some general relationships between material aspects such as polyimide structure, its molar mass, the content of azo dye, the value of d-spacing, the thickness of polymer film, and thermal cis-trans isomerization. The reversibility of the trans-cis-trans reaction was studied in 10 subsequent cycles and 100 cycles for the selected polymers. Studies of the reversibility of the trans-cis-trans reaction were realized by irradiation using two wavelengths of radiation λ = 365 nm (P = 2.9 W) and λ = 460 nm (P = 850 mW). To the best of our knowledge, this is the first article that comprehensively presents solid-state cis-trans isomerization for azo polyimides.