Theory of defect-induced localized exciton states in polyfluorenes

We outline a general theory for defect-induced localized exciton states in polyfluorenes. Working within the framework of the one-dimensional Frenkel exciton model, we characterize the defect as monomer that has a different optical transition frequency and modified nearest-neighbor interaction parameters. We obtain an exact expression for the energy of the localized exciton state in terms of the optical transition frequency and interaction parameters relative to those of the defect-free system. We also investigate the spatial extent of the localized states and their relative optical activity. The theory is used to analyze the fluorescence associated with ketonic defect sites in poly(di-n-octylfluorene) (PF8).