XPS studies of chemically synthesized polypyrrole-halogen charge transfer complexes

Abstract

Simultaneous polymerization and doping of pyrrole have been carried out in presence of a halogen electron acceptor, iodine (I2) or bromine (Br2), in aqueous dispersion or in acetonitrile at 0 to 4 °C to give PPY-I2 and PPY-Br2 charge transfer complexes. X-ray photoelectron spectroscopy (XPS) has been used to evaluate the degree of oxidation of the polypyrrole nitrogen atoms. The XPS results show that in both cases, not all the halogen dopants are available for oxidation. In the case of PPY-I2, as much as 34% of the total iodine present has undergone ring substitution in the polymer chain. Nitrogen atoms with one positive charge are formed when oxidized by the remaining halogen anions in a 1 to 1 ratio. Comparison between surface and bulk stoichiometries suggests that the dopant is distributed more evenly in PPY-Br2. © 1988.