One‐Step Carbonyl‐Locking Strategy for Multi‐Resonance Emitters Enabling Efficient, Narrowband Blue OLEDs

Efficient and narrowband blue multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters are highly attractive for wide color gamut organic light‐emitting diodes (OLEDs). Here, we strategically incorporate an electron‐deficient carbonyl lock at the para‐position of the nitrogen atom in the classical MR‐TADF skeleton by a simple one‐step carbonylation reaction with a high yield. Compared to the parent molecules, this design strategy not only reduces intramolecular charge‐transfer intensity, leading to blue‐shifted emission, but also effectively enhances molecular planarity and rigidity, thereby narrowing the emission spectra. As a result, the proof‐of‐concept emitters, namely CO‐BCzBN and CO‐DABNA, are developed, with emission peaks at 462 and 445 nm, and narrow the full widths at half maximum (FWHMs) of 16 and 18 nm, respectively, representing the first blue boron/nitrogen/carbonyl hybrid MR‐TADF emitters. The sensitized OLEDs based on CO‐BCzBN and CO‐DABNA achieve excellent blue electroluminescent performance, with the maximum external quantum efficiency (EQE max ) values of 37.9% and 22.8%, along with the Commission Internationale de l’Éclairage (CIE) coordinates of (0.133, 0.141) and (0.146, 0.078), respectively.