B─N Covalent Bonds and Twin‐Spiro Fused Design Strategy for the Construction of Narrowband Multiple Resonance Emitters

Abstract Developing the modified skeleton of multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters can feasibly regulate their optoelectronic properties. However, research on MR‐TADF materials incorporating B─N covalent bonds remains relatively limited. Herein, a strategy is first proposed utilizing the twin‐spiro conformation, a dispirofluorene acridine skeleton (DSAF), via the amine‐directed double borylation for framework fusion to construct MR‐TADF emitters, DSAF‐TBDPA and DSAF‐TBCz. B─N covalent bonds and twin‐spiro fusion are employed to enhance the structural rigidity of the molecular framework. Furthermore, the introduction of a twin‐spiro structure imparts steric hindrance, thereby weakening the π – π interactions and mitigating exciton quenching. As a result, DSAF‐TBDPA and DSAF‐TBCz exhibit narrowband emission with a full width at half maximum of 20 and 19 nm. The doped organic light‐emitting diodes (OLEDs) based on DSAF‐TBDPA and DSAF‐TBCz exhibit maximum external quantum efficiencies (EQE _max ) of 27.2% and 30.8%, respectively. These results underscore that molecular design tactics not only expand the diversity of MR frameworks but also deliver critical insights for the design of high‐performance OLED emitters.