Burning TADF Solids Reveals their Excitons’ Mobility tototo

Thermally Activated Delayed Fluorescence (TADF) compounds contribute to the light emission of an optoelectronic device by harvesting both their singlet and triplet states. But quenching limits such benefits at high current densities. In the case of cationic N-heterolytic carbene of Cu(I) bearing 2,2’-dipyridylamine, we create defects in its crystals by a strong laser irradiation, then investigate, by analysing its fluorescence decay as a function of temperature, the quenching mechanism and the exciton mobility. Using a time resolved version of the Perrin’s quenching model, we show that the quenching volume depends on temperature according to the singlet/triplet equilibrium. At room temperature, the singlet states are responsible for 75% of the quenching although they contribute only 2% to the excited state population. From the analysis of the decay curves, we show that the excitons are not mobile in the crystals and are quenched through Förster Resonant Energy Transfer (FRET). But usual equations does not hold and we show that, for experimental setups of reasonable quality, the signal coming from the non-quenched molecules can seen and used.