Poly(N-alkylcarbazole) synthesized from the corresponding 3,6 dihalide monomer using zerovalent nickel as a catalyst has an average value for its polydispersity of ca. 2. The electrochemical behaviour in solution is characterized by as many signals as weight populations in the crude sample. We have prepared, by selective solubilization in acetone, various samples having a low polydispersity tinder lower than 1.4) and studied their electrochemical properties when these compounds are solubilized in dichloromethane. We observed that the electrochemical behaviour of these samples with low polydispersity is much better defined than the crude samples but less well-defined than the only carbazole oligomer having a well-defined structure easily available, i.e. the 9,9'-diethyl 3,3' dicarbazyle. These results allow the study of the variation of the apparent diffusion coefficient versus the average molecular weight M-n. Finally, we show that the decrease of electrochemical activity of poly(N-alkylcarbazole) having a low polydispersity deposited as a thin layer on platinum as a function of the number of electrochemical cycles is less pronounced compared with a film of the crude product. Furthermore, this decrease is also less pronounced with higher molecular weight fractions. Thus, a decrease in the polydispersity as well as an increase in the molecular weight of the polymer may be helpful in the improvement of the life time of electrochromic devices. (C) 2000 Elsevier Science Ltd. All rights reserved.