Transition of polaron to bipolaron structure in conjugated polymers

Abstract

We describe the effects of removing one more electron from conjugated polymers with polarons. We use a Su-Schrieffer-Heeger model modified to include an external electric field and electron–electron interactions via a Parr-Pariser-Pople mean field Hamiltonian. Within the Unrestricted Hartree–Fock approximation, we study the dynamics performing numerical simulations. We have found that removing one electron from a conducting polymer bearing a single polaron leads to the creation of a structure that contains a bipolaron coupled to a breather. The bipolaron energy levels in the gap oscillate with higher amplitude due to the bipolaron–breather coupling. The bipolaron–breather pair can be decoupled through the action of an external electric field. Lattice oscillation modes are created due to the bipolaron motion and the energy levels associated to the bipolaron still oscillate, nevertheless, with smaller amplitude. The effects of the external electric field on the bipolaron–breather dynamics are studied by changing the electric field intensity.