Stability and behavior of poly-1-naphthol films towards charge transfer reactions

Abstract

Conducting poly-1-naphthol films (0.5–2.0 μm) showed a decreasing tendency for doping with film thickness. The average specific capacitance of poly-1-naphthol films formed by cyclic voltammetry in MeCN containing tetrabutylammonium perchlorate in the reduced dedoped state was found to be ∼ 10 mF cm −3 and increased on electrochemical oxidation (doping) to ∼ 60 mF cm −3. Stabilization of the polymer by repetitive cyclic voltammetry led to increase or decrease in the redox charge with number of cycles, depending on the final oxidation potential and in all cases, the peak separation decreased due to rearrangement of the polymer chains. The polymer doping/dedoping processes showed a pronounced increase in the diffusion coefficient of the charge transfer with thickness and a substantial difference between the doping and dedoping process. The doping process is controlled by an initial fast charge propagation step and followed by a slower step of anion insertion into the polymer film while in the dedoping only the anion removal from the film could be distinguished. The electron transfer for the redox [Fe(CN) 6] 4−/3− on the polymer films showed also a strong dependence on film thickness. It is inferred that the polymer film is composed of two layers; an inner compact layer (< 1 μm) which impedes to a larger extent the charge transfer reactions and an outer less compact and easily removable layer with more facile permeability. When the film is thickened, however, the inner layer is partially distorted and its barrier character towards charge transfer is gradually lost.