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 (EQEmax) 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.