Ultra‐Narrow Pure‐Green MR‐TADF Emitter with an FWHM of 12 nm Enables Superior‐Performance Top‐Emitting OLEDs with EQE Approaching 60%, Power Efficiency Over 300 lm W −1 , and CIE Coordinates of (0.14, 0.79)

ABSTRACT Achieving pure‐green organic light‐emitting diodes (OLEDs) with both precise spectral positioning and an ultra‐narrow full‐width at half‐maximum (FWHM) remains highly challenging, as red‐shifting emission into the pure‐green regime is often accompanied by enhanced excited‐state relaxation and spectral broadening. Herein, we report a molecular design strategy that reconciles green‐region red‐shift with intrinsic spectral narrowing through the synergistic integration of dibenzofuran fusion and cyano decoration within a meta ‐diboron framework. The proof‐of‐concept molecule DBFCN exhibits intrinsically ultra‐pure green emission in dilute toluene, centered at 519 nm with a very small FWHM of 12 nm, placing it among the narrowest green multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters reported so far. The bottom‐emitting OLEDs deliver a maximum external quantum efficiency (EQE max ) of 38.5% and pure‐green emission at 521 nm with an ultra‐narrow FWHM of 13 nm. Owing to the intrinsically ultra‐narrow emission and minimal spectral tail of DBFCN, photon loss in the top‐emitting (TE) configuration is effectively mitigated, leading to markedly enhanced device performance. Consequently, the TE‐device delivers a maximum power efficiency (PE max ) exceeding 300 lm W −1 and a current efficiency (CE max ) of 232.5 cd A −1 , while meeting the green BT.2020 color gamut.