High‐Performance Multi‐Resonance Thermally Activated Delayed Fluorescence Emitters for Narrowband Organic Light‐Emitting Diodes

Abstract Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters have drawn considerable attention because of their remarkable optoelectronic properties of high emission efficiency and narrow emission profile, and represent an active subject of cutting‐edge research in the organic electroluminescence (EL). However, the slow reverse intersystem crossing (RISC) rate of MR‐TADF emitter caused by the large energy gap (Δ E ST ) and small spin‐orbit coupling (SOC) matrix elements between the singlet and triplet excited states limits their further development in organic EL devices. Currently, innovative molecular design strategies have been developed including heavy atom integration, π‐extended MR framework and metal perturbation, and so on to improve the RISC process of MR‐TADF emitters for high‐performance EL devices. Here, an overview is presented on the recent progress of MR‐TADF emitters with fast RISC rate ( > 10 −5 s −1 ), with particular attention to the molecular design, optoelectronic properties, and device performance of organic light‐emitting diodes (OLEDs), which intends to systematize the knowledge in this subject for the thriving development of highly efficient MR‐TADF emitters. Finally, the challenges and future prospects of MR‐TADF materials are discussed comprehensively.