One‐Step Phosphine‐Oxide Post‐Modification of Multi‐Resonance Emitters for Efficient, Narrowband, Quenching‐Resistant OLEDs

Abstract Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) materials featuring high efficiency and narrowband emission are crucial for wide color‐gamut organic light‐emitting diodes (OLEDs), but they often suffer from complex synthesis and limited structural diversity. In this study, we report a one‐step, metal‐free phosphine‐oxide (P═O) post‐modification strategy to construct the first B/N/P═O fused MR‐TADF emitters, PO‐BCzBN and PO‐tFBN. This strategy introduces a covalent P═O lock, enhancing the rigidity of the π‐conjugation plane to maintain narrowband emission while simultaneously suppressing aggregation‐caused quenching (ACQ) through the steric hindrance introduced by the trigonal pyramidal geometry of sp 3 ‐hybridized P atom. PO‐BCzBN and PO‐tFBN show photoluminescence emission peaks at 466 and 493 nm with narrow full widths at half maximum (FWHMs) of 21 and 23 nm in solution, near‐unity photoluminescence quantum yields of 98% and 99%, rapid reverse intersystem crossing rates of 2.0 × 10 4 and 2.1 × 10 4 s −1 , and suppressed concentration quenching in films. Sensitizer‐free OLEDs based on PO‐BCzBN and PO‐tFBN achieve maximum external quantum efficiencies of 21.6%–34.2% (electroluminescence emission peaks, λ EL s, = 472–476 nm, FWHMs = 24–28 nm) and 28.3%–35.8% ( λ EL s = 496–500 nm, FWHMs = 26–27 nm) across a broad doping range (1–20 wt%), respectively, demonstrating superior resistance to spectral broadening and ACQ.