On the relation between conformational changes and electronic structure defects in polypyrrole

Using the semiempirical quantum-chemical AM1 method, the dependence of geometry and electronic structure on the torsion angle delta between neighbouring pyrrole rings of quaterpyrrole in various charge and spin states is investigated. The magnitudes of changes in the electronic structure of polypyrrole caused by geometrical changes of the chain may be comparable with those caused by charge and spin fluctuations. A limited amount of negative charge may be spontaneously stabilized on the polypyrrole chain due to chain deformations caused by solid state influences without any charged dopants. Charge fluctuations are most probably concentrated at nitrogen atoms. N-C bonds are less dependent on delta variations as well as on charge and spin perturbations than C-C bonds.