Significant enhancement of optical nonlinearity by quantum lattice fluctuations in pi -conjugated polymers

Interchain coupling effects on dynamics of photoexcitations in conjugated polymers

Within an extended Su-Schrieffer-Heeger model including interchain interactions and the extended Hubbard model, the dynamical relaxation of photoexcitations in two coupled conjugated polymer chains is investigated by using a nonadiabatic evolution method. Initially, one of the two chains is photoexcited and the other chain is in the dimerized ground state. Due to the interchain interactions, the electron and/or the hole can be transferred from one chain to the other chain. For weak interchain coupling, the dynamical evolution of the lattice on the photoexcited chain is similar to that found in an isolate single chain case. With interchain interactions increasing, the amplitude of the distortions on the photoexcited chain decreases, and simultaneously, that on the other chain gradually increases. Until stronger interchain coupling, the deformations of the two chains have almost the same amplitude. Besides intrachain polaron-excitons and intrachain oppositely charged polaron pairs as found in single chain case, interchain polaron-excitons and interchain separated charged polaron pairs are obtained. The results show that the yield of interchain products increases and that of intrachain products decreases with interchain coupling increasing. Totally, the yield of charged polarons (including intrachain oppositely charged polaron pairs and interchain oppositely charged polaron pairs) is about 25%, in good agreement with results from experiments.

Polaron dynamics in a system of coupled conjugated polymer chains

The motion of excitations such as polarons is believed to be of fundamental importance for the transport properties of conjugated polymers for the use in, e.g., polymer based LED's. We have investigated polaron dynamics in a system of coupled polymer chains in the presence of an external electric field. In particular, we focus on how a polaron migrates through the polymer lattice, i.e., the situation in which a polaron reaches a chain end and is scattered to the surrounding chains. We show that the outcome of this event strongly depends on the strength of the electric field, and we identify three different cases for the polaron migration.