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 (EQE(max)) 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.