Poly(aniline-co-diphenylamine and 5-aminosalicylic acid) with p-type and n-type doping segments is first synthesized via electrochemical copolymerization of aniline, diphenylamine (DPA) and 5-aminosalicylic acid (5-ASA) in a solution of N, N-dimethylformamide (DMF) and sulfuric acid; a potential separation between two doping states is >= 1V, depending slightly on pH in a pH range of 4.0 to 13.3. For simplicity, the product of the electrochemical copolymerization, i.e., poly(aniline-co-diphenylamine and 5-aminosalicylic acid), is called copolymer. Evidence for both doping types comes from results of cyclic voltammetry of the copolymer in the wide pH range and wide sweeping potential region. The p-type doping state of the copolymer is not only related to aniline units in the copolymer chain, but also related to the potential region of the cathodic scan. The copolymer is a mixture of oligomers that are proven by mass spectral analysis. The measurements of electron spin resonance (ESR) demonstrate that free radicals are present in the copolymer. In particular, the copolymer shows evident photoelectric response under visible light illumination in aqueous media. (C) 2014 Elsevier Ltd. All rights reserved.