Spatial imaging of singlet energy migration in perylene bis(phenethylimide) thin films

The migration length of singlet electronic energy excitations (excitons) in thin films of perylene bis(phenethylimide) (PPEI) has been measured by an imaging technique that incorporates near-field optical excitation and far-field fluorescence imaging. The observed energy migration lengths fall in the range of less than or equal to 50 to similar to 500 nm depending on sample morphologies. Sample morphology was controlled by "solvent annealing" and characterized by fluorescence NSOM and scanning force microscopy. The potential role of sample morphology in singlet energy migration is discussed. Additionally, the results reported herein are compared with a previous determination of singlet energy migration in PPEI.