Mechanistic modeling of exciton–exciton annihilation in the prototypical thermally activated delayed fluorescence emitter DMAC-TRZ

Organic light-emitting diodes (OLEDs) that are based on thermally activated delayed fluorescence (TADF) emitter molecules can potentially outcompete often-used OLEDs that are based on metalorganic phosphorescent emitters, as due to a larger radiative decay rate of TADF emitters, the efficiency loss at high current densities (“roll off”) due to bimolecular interaction processes can be reduced. However, so far no mechanistic model of these processes has been developed. Here, we develop such a model for exciton–exciton annihilation processes in the prototypical TADF emitter 10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9,9-dimethyl-9,10-dihydroacridine. Using kinetic Monte Carlo simulations to analyze the results of time-resolved photoluminescence experiments, singlet–singlet and singlet–triplet annihilation are shown to be well described as a Förster-type process with a Förster radius of 3.8 nm. This finding is shown to be consistent with results of first-principles quantum-chemical calculations. Triplet–triplet annihilation is found to be negligible under optical excitation.