Visible and Near-Infrared Electrochromic Polyamides and Polyimides Featuring a Phenothiazine-Triphenylamine Star-Shaped Architecture

An aromatic diamine monomer featuring a phenothiazine-triphenylamine starburst structure, referred to as 3,7-bis-[4-amino-4′-methoxydiphenylamino]-10-(4-(di(4-methoxyphenyl)amino)phenyl)phenothiazine (4), has been synthesized. This led to the formation of electroactive aromatic polyamides (6a and 6b) and polyimides (8a and 8b) through polycondensation reactions with the appropriate dicarboxylic acid and dianhydride monomers. The resulting polymers show excellent solubility in a range of organic solvents and exhibit remarkable thermal stability, with negligible weight loss noted up to 450 °C and high glass transition temperatures between 248 and 280 °C. During the first cyclic voltammetry (CV) scan, the polymers reveal four redox couples across a potential range of 0 to 1.6 V, exhibiting a color transition from pale orange at 0.47 V to purple-blue at 0.74 V, and finally to a deep purple-blue between 1.0 and 1.6 V. These polymers demonstrate outstanding redox and electrochromic stability, achieving a high coloring efficiency of up to 246 cm²/C in both the first and second oxidation states. Notably, no significant loss in current density in the CV curves or optical contrast of the polymer films was observed after 1200 switching cycles. Furthermore, they demonstrate intense near-infrared absorption at approximately 1043 nm upon oxidation.