Extending the π‐Skeleton of Multi‐Resonance TADF Materials towards High‐Efficiency Narrowband Deep‐Blue Emission

Abstract Multi‐resonance TADF (MR‐TADF) emitters are promising for high‐resolution OLEDs, but the concurrent optimization of excited‐state dynamics and color purity remains a tough challenge. Herein, three deep‐blue MR‐TADF compounds (BN1–BN3) featuring gradually enlarged ring‐fused structures and increased rigidity are accessed by lithium‐free borylation in high yields from the same precursor, with all the emitters possessing CIEy coordinates below 0.08. Structure–property investigations demonstrate a strategic improvement of the oscillator strength (fosc) and acceleration of the reverse intersystem crossing (RISC) process by extending the π‐skeleton, where BN3 realizes a maximum external quantum efficiency (EQE) of 37.6 % and reduced roll‐off, thus showing the best efficiency reported for deep‐blue TADF OLEDs. The internal regulation of the efficiency and color purity of these compounds validate the general effectiveness to achieve advanced deep‐blue narrowband emitters with higher‐order boron/nitrogen‐based MR motifs.