Exciton confined states in conjugated polymers studied by spectroscopic fluorescence polarization measurements

Spectroscopic fluorescence polarization (P) measurements have been used to investigate exciton dynamics in conjugated polymers. We apply photoluminescence anisotropy to ensembles of non-interacting organic semiconductor molecules to explore exciton migration. An experimental observation shows linearly decreasing P values as the emission wavelength increases in partially oxidized poly[2-methoxy-5-(2-ethyloxy)-1,4-phenylenevinylene] (MEH-PPV) ensemble molecules. We discuss the origin of the experimental data with a computational simulation and P values for single chromophore perylene diimide dye molecules. We propose that the physical mechanism responsible for this behavior is the presence of exciton confined and blocking states at blue-shifted emission sites, which arise from excitons in partially oxidized parts of MEH-PPV.