Electronic and magnetic properties of polypyrrole films depending on their one-dimensional and two-dimensional microstructures

We report on the electronic and magnetic properties of polypyrrole films with a one-dimensional and two-dimensional microstructure. Polypyrrole films as well defined and stable polymers are studied. The aim of this work is an explanation of the macroscopic conductivity based on microscopic and electronic structure. In particular we attribute the high d.c. conductivity, the frequency-independent a.c. conductivity and the weak temperature dependence of the conductivity to the existence of two-dimensional crosslinked areas. We characterize the polypyrrole films by photoelectron spectroscopies (X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS)), by electron paramagnetic resonance (EPR) spectroscopy, and by the frequency- and temperature-dependent conductivity measurements. We compare the results to the corresponding properties of one-dimensional polypyrrole films. The two-dimensional films consist of a graphitic electronic structure in which pyrrole monomers either contribute to the two-dimensional π-system or maintain their monomeric character, as characterized by photoelectron spectroscopies. The EPR data reveal magnetic centers that show a Curie-like susceptibility and a weak Pauli contribution, and the latter does not contribute to the conductivity mechanism. The EPR linewidth is extraordinarily sharp and reversibly reflects the dynamics of the interaction to oxygen.