Structurally Tunable Donor−Bridge−Fluorophore Architecture Enables Highly Efficient and Concentration‐Independent Narrowband Electroluminescence

Abstract Luminescent materials with narrowband emission have extraordinary significance for developing ultrahigh‐definition display. B–N‐containing multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials are strong contenders. However, their device performances pervasively encounter detrimental aggregation‐caused quenching effect that is highly vulnerable to doping concentration, complicating device fabrication. Therefore, constructing highly efficient and concentration‐independent MR‐TADF emitters is of pragmatic importance for improving device controllability and reproducibility, simplifying manufacturing procedures, and conserving production costs. Here, by systematic arrangement of donor triphenylamine and fluorophore BNCz on distinct bridges, a spatial confinement strategy has been developed with a donor−bridge−fluorophore architecture. Structurally fine modulation and progressive evolution to construct molecular entities with congested steric hindrance effect that can suppress intermolecular interactions without substantially affecting the luminescence tone of fluorophore BNCz, resulting in highly efficient and concentration‐independent narrowband emitters; through isomer engineering, two isomers BN‐PCz‐TPA and TPA‐PCz‐BN with different crystal stacking patterns are synthesized by altering the connection mode between triphenylamine and BNCz. As a result, BN‐PCz‐TPA‐based device showcases maximum external quantum efficiency (EQE) of 36.3% with narrow full‐width at half‐maximum of 27 nm at 10 wt% doping concentration. Even at 20 wt% doping concentration, the maximum EQE remains at 32.5% and the emission spectrum is almost unchanged.