The first evidence of redox activity of polyimide systems modified with azo groups with photo-induced response

Aromatic azo-copolyimides based on hexafluoroisopropylidene dianhydride and a mixture of 2,4-diamino-4′-methylazobenzene and different aromatic diamines in 0.25:0.75 M ratio were studied with regard to their photo-optical and electrochemical properties. Absorbance spectra within the UV-Vis range of polymer solutions along with the UV-Vis-NIR transmission and reflectivity of polymer films were measured. Thus, the optical parameters such as energy gap, yellowness and refractive index were obtained for polymer films, while the position of absorption bands was comparatively discussed for polymer solutions in correlation with the structural motif. Trans-cis photo-isomerization of azobenzene moiety was observed and thoroughly analysed for both polymer solutions and thin films through systematic studies of UV-Vis and fluorescence spectral features. On the other hand, the electrochemical activity (i.e., oxidation and reduction capability) of the understudy azo-copolyimides was explored by cyclic voltammetry (CV) measurements both in fluid and solid state. Owing to their ability to promote favorable properties, applications in electronic devices with photo-controllable functions are foreseen.