Optical signature of delocalized polarons in conjugated polymers

Quantum-chemical calculations, incorporating both electron-phonon and elect ron-electron effects, are performed on two-chain model aggregates to assess the influence of interchain interactions on the nature of the singly charg ed species (polarons) in organic conjugated polymers. In symmetric cofacial dimers with fixed intermolecular distances, our theoretical approach leads to polarons fully delocalized over the two conjugated chains. Such a deloc alization strongly affects the geometric and electronic relaxation phenomen a induced by charge injection, which in turn leads to a dramatic spectral r edistribution of the linear absorption cross section. Optical signatures fo r delocalized polarons in conjugated materials are identified from our theo retical description and compared to experimental data from optical charge m odulation spectroscopy; these are fingerprints for the degree of interchain order, a decisive factor in the achievement of high charge carrier mobilit ies in polymer-based field-effect transistors.