Electrochemical Properties of Electropolymerized Poly(1-pyrenamine) Films

The electropolymerization of 1-pyrenamine (PA) in an acetonitrile solution led to the polymeric film formation on electrode surfaces. The chemical, spectroscopic, electrical and electrochemical characterization of the resulting poly(1-pyrenamine) (PPA) films was carried out. The number-average molecular weight of the PPA film, measured by gel permeation chromatography, was 1.8×103, corresponding to the degree of the polymerization of ca. 8. The PPA films were polymer-anion composites which contained ca. 0.3 anions (e.g., BF4−) per repeating aromatic unit, which is considered to be composed of three PA molecules. The oxidized form of the PPA film displayed the ESR response. The g factor was 2.0082 and the concentration of radical in the PPA film was determined to be 4.8×1019 e−g−1. The conductivities of the PPA films in the dry state at 300 K were in the range 10−11–10−10 S cm−1. The PPA film was electroactive in an aqueous solution as well as in a non-aqueous solution. The cyclic voltammetric responses depended on pH of aqueous solutions and supporting electrolyte in non-aqueous solutions. The thickness(φ) of the PPA film and the surface concentration(Γ) of the electroactive site in the PPA film were proportional to the amount (Q) of the charge passed during the electrolysis (when Q<ca. 120 mC cm−2). The volume concentrations of the electroactive site were 9.7×10−4 and 1.7×10−3 mol cm−3 for the PPA films prepared in the NaClO4 and TBABF4 (tetrabutylammonium tetrafluoroborate) electrolytes, respectively. From the normal pulse voltammetric, potential-step chronoamperometric and potential-step chronocoulometric experiments of the PPA films in a 0.2 M NaClO4 aqueous solution (pH 1.0), the effective apparent diffusion coefficient (Dapp) for the diffusion-like charge transport within the PPA films, and the standard rate constant (k°) and anodic transfer coefficient (αa) of the heterogeneous electron-transfer reaction between the In2O3 electrode and the electroactive site in the PPA film were estimated to be (1.5±0.5)×10−10 cm2 s−1, (1.9±0.4)×10−5 cm s−1 and 0.67±0.03, respectively.