Influence of oxygen on the paramagnetic properties of polypyrrole layers

Different polypyrrole films with a defined one- and two-dimensional microstructure are prepared by electrochemical polymerization. In as prepared films paramagnetic species are formed which have been investigated by paramagnetic electron spin resonance (ESR) spectroscopy. Single line ESR spectra with a line width of ΔB = 0.022 mT in vacuum, a spin concentration of N = 3 × 1019 spins/g and a g-factor of g = 2.0026 were measured. presence of oxygen the ESR linewidth of polypyrrole increases almost linearily with increasing oxygen pressure by a factor of more than 10, resulting in a line width of ΔB = 0.28 mT at atmospheric conditions. There is also a time dependance of the increasing ESR line width influenced by the oxygen diffusion processes in the different polypyrrole structures. The ESR line width varies highly reversibly upon evacuation. Successive repetitions of oxygen exposure/pump off procedures show an excellent reproducibility. This reversible reaction of the paramagnetic centres in polypyrrole films upon interaction with oxygen opens the possibility for an application of these polymer films as oxygen sensors.