Narrowband TADF emitters with high utilization of triplet excitons: theoretical insights and molecular design.

Narrowband emitters with thermally activated delayed fluorescence (TADF) features, known as multi-resonant TADF (MR-TADF) emitters, are drawing increasing research interest owing to their properties of high efficiency and excellent color purity. However, MR-TADF-based devices often face serious efficiency roll-off at high luminance intensity, which could be attributed to undesired triplet-triplet annihilation (TTA) caused by the structural planarity and relatively small reverse intersystem crossing rate constants () of MR-TADF emitters. Herein, combining a sp-C inserted strategy to suppress harmful bimolecular interactions and chalcogens to improve the , a series of asymmetric narrowband emitters, namely, DMAC-O, DMAC-S, and DMAC-Se, have been theoretically designed to break the slow rate-limiting step of of experimental BN-DMAC.