Dynamics and coherence of photoexcited states in polyfluorene films with ordered chain phases

Abstract

Understanding the optical and electronic excitations in conjugated polymers, their delocalization, and dynamics is of paramount importance for improving the performance of optoelectronic devices. The structure of a conjugated polymer in the solid state, the presence of ordered domains, and conformational subunits strongly affect the exciton and polaron interactions. The effect of the crystalline structure of polyfluorene films on exciton dynamics was studied using a combination of electrochemical and spectroscopic methods. Optoelectronic alterations caused by the p-doping process strongly suggest that the electrochemical charge injection occurs mainly in the more ordered β-phase. Evidence for the presence of either α- or β-phase is supported by the different behavior of the fluorescence quenching at increasing doping levels (the quenching elements appear more homogeneously distributed in the α-PFO phase). Estimated singlet exciton coherence lengths indicate that it delocalizes over 20 repeat units in the α-PFO phase, but it extends only over 14 units for β-PFO.