Ultrafast combined dynamics of Förster resonance energy transfer and transient quenching in cationic polyfluorene/fluorescein-labelled single-stranded DNA complex

The combined dynamic process of Förster resonance energy transfer and transient quenching is quantified in the time-resolved fluorescence of cationic polyfluorene/fluorescein-labelled single-stranded DNA complex. We found that the radiation boundary condition fails to predict transient quenching due to a single quenching rate at the encounter distance between a fluorophore and a quencher; however, the predictions of the micellar kinetics model were in good agreement with the measured time-resolved fluorescence as an alternative to the complicated distance-dependent quenching model. The combined dynamics model enables the separation of the rate of Förster resonance energy transfer from that of transient quenching, by which we obtained an accurate estimation of the donor-acceptor intermolecular distance (41±1.6 Å) in comparison with the Förster distance (43 Å).