Two-dimensional electronic excitations in self-assembled conjugated polymer nanocrystals

Several spectroscopic methods were applied to study the characteristic prop erties of the electronic excitations in thin films of regioregular and regi orandom polythiophene polymers. In the regioregular polymers, which form tw o-dimensional lamellar structures, increased interchain coupling strongly i nfluences the traditional one-dimensional electronic properties of the poly mer chains. The photogenerated charge excitations (polarons) show two-dimen sional delocalization that results in a relatively small polaronic energy, multiple absorption bands in the gap where the Lowest energy band becomes d ominant, and associated infrared active vibrations with reverse absorption bands caused by electron-vibration interferences. The relatively weak absor ption bands of the delocalized polaron in the visible and near-infrared spe ctral ranges may help to achieve Laser action in nanocrystalline polymer de vices using current injection.