Substituent Effect on Electrochemical and Electrochromic Behaviors of Ambipolar Aromatic Polyimides Based on Aniline Derivatives

Three series of new ambipolar polyimides containing aniline derivatives with different degree of 4-methoxyphenyl substituent showing anodically/cathodically electrochromic characteristic were prepared from the polycondensation of three diamine monomers—4,4′-bis[(4-aminophenyl)amino]diphenylamine ( 3 ), 4,4′-bis[(4-aminophenyl)amino]-4″-methoxytriphenylamine ( 3 ′), and 4,4′-bis[4-aminophenyl(4-methoxyphenyl)amino]-4″-methoxytriphenylamine ( 3 ″)—with various commercially available tetracarboxylic dianhydrides. In addition to the high glass-transition temperatures ( T g, 246–339 °C), thermal stability, and solution processability, the resulting polyimide films exhibited ambipolar electrochromic behavior. The nonconjugated TPA-based polyimides III revealed more stable electrochemical oxidation behavior and better electrochromic reversibility than conjugated DPA-based corresponding polyimides I due to the additional phenyl ring providing the route to stabilize the cation radical formed during oxidation.