Triplet exciton migration in a conjugated polyfluorene

The diffusion and triplet energy relaxation in amino endcapped poly [9,9-bis(2-ethylhexy1)fluorene-2,7-diyl] has been studied using photoluminescence and photoinduced absorption, both time-resolved covering ten decades of time, dependent on temperature, excitation dose, and concentration. The results are analyzed employing the concept of dispersive hopping in a Gaussian distribution of states (DOS), characterized by width delta of 40 meV. It is found that the initial photogenerated triplet population in the polymer films decays fairly equally by triplet-triplet annihilation and intrinsic monomolecular decay, respectively. In the latter case, the triplet excitons survive the initial 100 ms either in trap states outside the DOS at ambient temperature or within the DOS at low temperature. Further, it is clearly found that triplet migration in this conjugated polymer is both an intrachain and interchain process. Interchain hopping of triplet excitons must occur, which subsequently leads to the observation of delayed fluorescence. The nature of interchain hopping of the triplets is discussed.