Effects of the electric field on the self-trapping excited states in conjugated polymers

We demonstrated that electric fields have strong impacts on the self-trapping excited states in conjugated polymers by numerically simulated calculations. Applied electric fields induce a displacement of positive and negative charges in a self-trapping excited state. Weak or moderate electric fields transfer part of the charges, so the self-trapping excited states in conjugated polymers are polarized. The degree of polarization increases linearly with the electric field E. The polarization of single-excited states is normal. It is worth to note that a self-trapping biexcited state shows negative polarization, i.e., the negative charges move along the direction of the electric field, while the positive charges drift in the opposite direction. Such behavior, which would be of interest both fundamentally and technologically, can be understood based on the quantum theory of polarization. Strong fields transfer all the charges in a self-trapping excited state, leading to the field dissociation of self-trapping excited states. The result is consistent qualitatively with the recent relevant experiments in conjugated polymers.