Electronic structure of pyrrole-based conducting polymers: An electron-energy-loss-spectroscopy study

Abstract

Pyrrole-based conducting polymers have been investigated by high-resolution electron-energy-loss spectroscopy and by electron diffraction. The evolution of the π-electron band structure as a function of the oxidation can be explained in terms of a bipolaron model. Strongly oxidized polypyrrole is not a metal, but has two narrow bands in the gap which can be assigned to bipolaron bands. The dielectric functions of electrochemically reduced polypyrrole films are well described by a linear-combination-of-atomic-orbitals complete-neglect-of-differential-overlap calculation on oligomers. The treatment of as-grown oxidized polypyrrole films by alkali metals leads to almost neutralized and not to n-type doped films. A reaction of the alkali-metal atoms with the nitrogen atoms is observed. The treatment of oxidized polypyrrole with NaOH does not change the π-electron band structure on the carbon atoms but leads again to a reaction on the nitrogen atoms.