Triazolotriazine-based thermally activated delayed fluorescence materials for highly efficient fluorescent organic light-emitting diodes (TSF-OLEDs).

A new type of triazolotriazine acceptor has been designed to construct highly efficient TADF materials by fusing triazine and triazole together and achieve the state-of-the-art performance yellow TSF-OLEDs. [Display omitted] Thermally activated delayed fluorescence (TADF) sensitized fluorescent organic light-emitting diodes (TSF-OLEDs) have shown great potential for the realization of high efficiency with low efficiency roll-off and good color purity. However, the superior examples of TSF-OLEDs are still limited up to now. Herein, a trade-off strategy is presented for designing efficient TADF materials and achieving high-performance TSF-OLEDs via the construction of a new type of triazolotriazine (TAZTRZ) acceptor. The enhanced electron-withdrawing ability of TAZTRZ acceptor, fused by triazine (TRZ) and triazole (TAZ) together, enables TADF luminogens with small singlet-triplet energy gap (Δ E ST) values. Meanwhile, the increased planarity from the TRZ-phenyl linkage (6:6 system) to the TAZ-phenyl linkage (5:6 system) can compensate the decrease of oscillator strength (f) while lowing Δ E ST , thus achieving a trade-off between small Δ E ST and high f. As a result, the related TSF-OLED achieved an extremely low turn-on voltage of 2.1 V, an outstanding maximum external quantum efficiency (EQE max) of 23.7% with small efficiency roll-off (EQE 1000 of 23.2%; EQE 5000 of 20.6%) and an impressively high maximum power efficiency of 82.1 lm W−1, which represents the state-of-the-art performance for yellow TSF-OLEDs. [ABSTRACT FROM AUTHOR]