A Tetrahedral Bisacridine Donor Enables Fast Radiative Decay in Thermally Activated Delayed Fluorescence Emitter

Achieving high efficiency and low efficiency roll-off simultaneously is of great significance for further application of thermally activated delayed fluorescent (TADF) emitters. A balance between radiative decay and reversed intersystem crossing must be carefully established. Herein, we propose a qunolino-acridine (QAc) donor composing two acridine with both planar (pAc) and bended (bAc) geometries. Combining with triazine, a TADF emitter QAc-TRZ is assembled. The pAc provides a well interaction with triazine which ensures a decent TADF behavior, while the bAc offers a delocalization of highest occupied molecular orbital (HOMO) which guarantees an enhancement of radiative decay. Remarkably, QAc-TRZ enables a highly efficient organic light emitting diode (OLED) with maximum external quantum efficiency (EQE) of 37.3 %. More importantly, the efficiencies under 100/1000 cd m(-2) stay 36.3 % and 31.7 %, respectively, and remain 21.5 % even under 10 000 cd m(-2).

Automated summary

Simultaneously achieving high efficiency and low efficiency roll-off is crucial for the further application of thermally activated delayed fluorescent (TADF) emitters. This study proposes a quinolino-acridine (QAc) donor, composed of two acridine units with planar (pAc) and bended (bAc) geometries, combined with triazine to assemble a TADF emitter QAc-TRZ. The pAc ensures decent TADF behavior through interaction with triazine, while the bAc enhances radiative decay through delocalization of the highest occupied molecular orbital (HOMO). Notably, QAc-TRZ enables a highly efficient organic light emitting diode (OLED) with a maximum external quantum efficiency (EQE) of 37.3%, and maintains efficiencies of 36.3% and 31.7% under 100/1000 cd m(-2), respectively, even at 10,000 cd m(-2).