Stepwise One‐Shot Borylation Reactions for Intersecting DABNA Substructures Exhibiting Bright Yellow‒Green Electroluminescence with EQE Beyond 40% and Mild Roll‐Off

Boron/nitrogen (B/N)‐doped polycyclic aromatic hydrocarbons (PAHs) with the multiple resonance (MR) effect are promising for organic light‐emitting diodes (OLEDs) because of their narrowband emission and thermally activated delayed fluorescence (TADF) characteristics. Nevertheless, exploring the variety of such emitters is challenging because of the tricky and limited synthetic protocols. Herein, we designed a novel B/N‐doped PAH, L‐DABNA‐1, whose backbone (L‐DABNA) could not be achieved via conventional routes (e.g., one‐pot borylation or one‐shot borylation). We successfully synthesized it through stepwise one‐shot borylations with precisely introducing decorations. The unique MR backbone with intersecting DABNA substructures sharing an aniline group, avoiding any para‐N‐π‐B motif, allows L‐DABNA‐1 to maintain narrowband TADF emission while significantly redshifting to the yellow–green region with a reverse intersystem crossing rate (kRISC) of 1.28 × 105 s−1. An L‐DABNA‐1‐based OLED device achieved a maximum external quantum efficiency (EQE) of over 40% and maintained a high EQE of 36.3% at 1000 cd m−2, with a current efficiency reaching ~170 cd A−1. This work not only demonstrated the great potential of stepwise borylations in synthesizing B/N‐doped PAH backbones, expanding their chemical space, but also provided a promising pathway for exploring MR‐TADF emitters at longer wavelengths.