Time-resolved fluorescence studies and Monte Carlo simulations of relaxation dynamics of photoexcitations in a polyfluorene film

Time-resolved fluorescence spectroscopy is used to investigate relaxation of electronic excitations in films of a π-conjugated polyfluorene polymer in the ps time domain. Results are consistent with theoretical predictions based on a model for relaxation of the excitations by incoherent hopping between localized states through Förster type energy transfer with a Förster radius R0∼20 Å. Excitons created by a photon with an energy <2.92 eV are found to remain immobile during their lifetime. In addition the measurements indicate that for excitation energies >2.94 eV additional relaxation processes, ascribed to ultrafast intrachain vibrational relaxation, are operative.