Delocalised electrons along the conjugated backbone
of polypyrrole result in an extended pi-system which is
 filled with valence electrons. Adding or removing electrons
from the pi-system (doping) produces a charged unit called
a bipolaron unit which is cabable of conducting electricity.

Optical properties are also affected by electron delocalisation
as they respond to changes in applied potential, temperature,
solvent and binding to other molecules.