Theoretical design of small bandgap polypyrrole derivatives

In the framework of our efforts to design new polymeric materials that would be intrinsically (that is, without doping) good electrical conductors, we have investigated new polypyrrole derivatives. These are formed by pyrrole rings separated by one and three conjugated carbons. The geometries of the chains are optimized with the MNDO (Modified Neglect of Diatomic Overlap) method and are then used as input for the VEH (Valence Effective Hamiltonian) band structure calculations. Our result indicate that these systems possess bandgaps as small as 1.0 eV, i.e. about three times lower than in the parent polypyrrole system. Interest in these compounds is further increased by the existence of synthetic routes to produce them.