Toward Narrow‐Band, Stable Blue MR‐TADF Emission via Combined Heterocyclic Analogues Marching B.T.2020

Abstract The development of efficient and stable ultra‐narrowband pure‐blue multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters is critical for next‐generation wide‐gamut OLED displays. Herein, we present a molecular design strategy that enhances emitter stability and efficiency by reinforcing the weak C─N bonds through selective incorporation of heterocyclic carbazole ( Cz ) units into the MR framework. Two proof‐of‐concept emitters, m‐Cz‐DABNA and tBu‐Cz‐DABNA , were synthesized via high‐yield, lithium‐free borylation. These emitters exhibit pure‐blue emissions at 453 and 463 nm with narrow full‐width at half‐maximums (FWHMs) of 24 and 21 nm in solution and high photoluminescence quantum yields (PLQYs) of 88% and 95%, respectively. OLED devices based on m‐Cz‐DABNA and tBu‐Cz‐DABNA show emissions at 456 nm (FWHM 24 nm, EQE max 23%, CIEy 0.06) and 467 nm (FWHM 24 nm, EQE max 26%, CIEy 0.10), respectively, holding among the highest efficiencies for blue OLEDs without sensitizers. Notably, the tBu‐Cz‐DABNA ‐based device shows an LT 90 of ∼81 h at 1000 cd m − 2 (EQE 8.95%), representing one of the longest operational lifetimes for blue fluorescent OLEDs with CIEy ≤ 0.10. These results demonstrate a versatile and scalable molecular design strategy for the realization of high‐efficiency, long‐lifetime blue OLEDs approaching the BT.2020 color standard.