The Design of Fused Amine/Carbonyl System for Efficient Thermally Activated Delayed Fluorescence: Novel Multiple Resonance Core and Electron Acceptor.

Multiple resonances induced thermally activated delayed fluorescence (MR‐TADF) has great advantages in high color purity display. Up to now, current MR‐TADF emitters are only based on the boron‐nitrogen‐containing fragment. Reported herein is a novel class of MR‐TADF emitter, quinolino[3,2,1‐de]acridine‐5,9‐dione (QAO), realized by the opposite resonance effect of the carbonyl and the nitrogen atoms, which is also the smallest TADF emitter reported so far. The QAO‐based pure blue organic light‐emitting diode achieves a maximum external quantum efficiency (EQEmax) of 19.4% with a small full width at half maximum of 39 nm. Moreover, tert‐butyl modified QAO can be employed as an efficient electron acceptor to construct an efficient yellow‐green evaporation and solution process feasible TADF emitter, 7‐(tert‐butyl)‐3,11‐bis(9,9‐dimethylacridin‐10(9H)‐yl)quinolino[3,2,1‐de]acridine‐5,9‐dione (QAO‐DAd), with significantly improved performance as compared to the previous flexible diketone‐based emitters. A novel class of multiple resonance induced thermally activated delayed fluorescence (MR‐TADF) emitter (QAO) is developed, by using the opposite resonance effect of the carbonyl group and the nitrogen atom. Moreover, QAO can be employed as an efficient electron acceptor to construct traditional donor–acceptor–donor type TADF emitter, QAO‐DAd, and then achieve high performances in evaporation and solution‐processed devices. [ABSTRACT FROM AUTHOR]