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

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 sp³-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 × 10⁴ and 2.1 × 10⁴ 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_ELs, = 472-476 nm, FWHMs = 24-28 nm) and 28.3%-35.8% (λ_ELs = 496-500 nm, FWHMs = 26-27 nm) across a broad doping range (1-20 wt%), respectively, demonstrating superior resistance to spectral broadening and ACQ.