Models of Coulomb screening and exciton binding in conjugated polymers

The effects of interchain interactions on the exciton binding energy are investigated using a model system consisting of a solvent polyene with 24 carbon atoms and a solute polyene with between 2 and 18 carbon atoms, separated by 4 Angstroms. It is shown that the time scales of electron-hole motion on the solute and the polarization of the solvent chain are such that a separation of time scales, for instance by screening the electron-hole potential, is not valid. Using a model that does not assume a separation of time-scales, interaction with the single solvent chain lowers the exciton binding energy by 0.36eV. Given this large value for a single solvent chain, it seems likely that interchain interactions play an important role in establishing the solid-state exciton binding energy.