Electrochemical synthesis of polycarbazole, having better stability and electrochromic activity, in dichloromethane containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) is reported at 1.4 V versus Ag/AgCl. The electrochemistry based on cyclic voltammetric measurements in dichloromethane containing TBAP show redox behavior of the polymer associated to doping and de-doping of ClO 4
Ϫ ion within the polymer interstices. The polycarbazole matrix obtained by the potentiostatic and potentiodynamic modes of electropolymerization is characterized based on scanning electron microscopy, differential calorimetry, and infrared spectroscopy. De-doping of the polymer is studied by electrochemical reduction in TBAP-free dichloromethane followed by incubation of the polymer film in 1 M aqueous KCl solution for 24 h. The open circuit potential (OCP) of doped and de-doped polycarbazole modified electrode under the present experimental conditions is found to 462 and 19 mV, respectively, versus SCE in 0.1 M NH 4 NO 3 . The de-doped polymer shows remarkable sensitivity and selective to Cu(II) ion compared to its sensitivity for Fe 3ϩ , Ni 2ϩ , Co 2ϩ , Pb 2ϩ , and Cu ϩ ions. A typical response of the de-doped polymer electrode to Cu(II) ion is reported. On the other hand, ClO 4 Ϫ doped polymer is used in the development of solid-state K ϩ ion sensors using dibenzo-18-crown-6/valinomycin as a neutral carrier-based, plasticized poly vinyl chloride matrix membrane assembled over a polymer-modified electrode. The doped polymer under this condition helps in maintaining charge stabilization across Pt/polymer and polymer/PVC interfaces. The lowest detection limit for the potassium ion sensor is 5 ϫ 10 Ϫ5 M with a slope of 58 mV/decade for valinomycin-based sensor and 6.8 ϫ 10 Ϫ5 M with a slope of 54 mV for dibenzo-18-crown-6 carriers with a wide linearity. The typical potentiometric results on the sensitivity, detection limits, and OCP to K ϩ ion recorded using present polymer are compared with the data recorded earlier using polyindole and a similar neutral carrier-based PVC membrane. A comparison on electrode kinetics of these two polymer-modified electrodes also has been made using the data on Tafel plots to study the relative kinetic polarizability based on ion-exchange currents.