Electric field effect on energy transfer monitored by bimolecular annihilation

In conjugated polymers excited singlet states are known to dissociate into polarons upon application of an electric field. We show that for excitation intensities exceeding 100 mu J cm(-2) in polyfluorene, this is not the only mechanism of field-induced decrease in the singlet population. Bimolecular annihilation is enhanced via increased overlap between singlet emission and absorption spectra due to Stark effect. We discuss the implications for Forster resonant energy transfer.