The electrochemical and electrochromic properties of poly(ether naphthalimide)s were studied and compared with related model compounds. The electroactive sites within the poly(ether naphthalimide)s were identified to be ketone and imide groups. The stepwise coloration process, colorless-red-dark blue corresponding to the neutral, radical anion and dianion species, was found to be related to the first reduction of the imide group and the second reduction of the ketone group. Based on this new polyimide a high-contrast switch between colorless and red or colorless and dark blue can be achieved and controlled electrically. (C) 2001 Elsevier Science Ltd. All rights reserved.