Novel rapid switching and bleaching electrochromic polyimides containing triarylamine with 2-phenyl-2-isopropyl groups

A series of novel organosoluble polyimides and copolyimides with a propeller-shaped triarylamine unit were prepared from diamine and various aromatic dianhydrides via direct polycondensation. All of the polymers possessed tough, flexible, and strong films with high molecular weights. The polyimide and copolyimide films revealed electrochromic characteristics, with a color change from pale yellowish at its neutral state, to green, and finally to blue at its oxidized state, at applied potentials ranging from 0 to 1.50 V. The polyimide (Ib) film exhibited switching times of 4.5 s at 1.08 V at 424 and 877 nm and 1.9 s for fast bleaching due to a pendent substituted 2-phenyl-2-isopropyl group. Cyclic voltammetry (CV) of the polymer films showed two reversible redox couples at potentials of 0.91-0.99 V and 1.30-1.38 V, respectively. The CV results of the model compound M1 and model polyimide M2, were not a match to the oxidation peaks of polyimide Ib, indicating that the contribution of the oxidation was not only from the electron removal of nitrogen atoms.