Electrochemical and photoelectrochemical response of electrodes coated with LB films of an azopolymer

Abstract

This paper describes the electrochemical and photoelectrochemical behaviour of electrodes coated with Langmuir–Blodgett (LB) films of an azopolymer. The coating material used is a pyridine azopolymer (PAzPy) obtained by free radical polymerization of 6-[2-(4-pyridyazo)phenoxy]hexyl methacrylate (AzPy). Cyclic voltammetry experiments of LB films deposited at several transference surface pressures were performed to analyze the effect of the molecular packing on the electrochemical response. The influence of the pH of the electrolytic solution was also considered. AFM images have helped in the interpretation of the molecular architecture influence on the redox activity of the films. From the experimental results it was concluded that PAzPy is situated with the nitrogen from the pyridine group close to the ITO electrode surface in the LB films, which allows a direct electron transfer between the electrode surface and the azobenzene group leading to a quick electrochemical response of the films. The azobenzene electrochemical activity and the kinetics of the process are also highly dependent on the proton transfer process between the electrolytic solution and the azobenzene unit. The efficiency of the proton transfer process is determined by the pH of the electrolytic solution as well as by the molecular architecture of the film. The results presented in this paper show that, under optimal conditions, both the percentage of electroactive azobenzene chromophores and the standard heterogeneous rate constant of electron transfer are higher for PAzPy arranged in LB films compared with the values so far reported for azobenzenes of lower molecular weight.