Design of a Novel Selenium‐Containing Spiro Donor for Narrowband Blue Thermally Activated Delayed Fluorescence Emitters in OLEDs

Achieving high‐efficiency and narrowband deep‐blue emission is of great significance for organic light‐emitting diodes (OLEDs). Herein, a novel selenium‐containing spiro‐acridine donor, DspiroSe, is designed for constructing highly efficient blue emitters. The spiro structure of DspiroSe contributes to suppressed aggregation‐caused quenching, while the selenium atom provides heavy‐atom effect. By attaching DspiroSe to a multiple resonance skeleton with different linkage strategies, two isomeric emitters sSeDDBN and PsSe‐DABNA are obtained, which show promise as candidates for blue OLEDs. Note that the different linkage methods of DspiroSe enable tuning of the emission spectrum from sky‐blue to deep‐blue, with PsSe‐DABNA demonstrating exceptional deep‐blue emission characterized by a full‐width at half‐maximum of 18 nm and a peak wavelength of 445 nm in solution. Both sSeDDBN and PsSe‐DABNA exhibit high photoluminescence quantum yields exceeding 90% in films, and OLEDs using them as emitters achieve maximum external quantum efficiencies (EQE max ) of 26.5% and 14.6%, respectively. By utilizing a TADF assistant host, the EQE max further increases to 28.5% for sSeDDBN and 19.1% for PsSe‐DABNA. Notably, PsSe‐DABNA based OLEDs exhibit excellent color purity with Commission Internationale de l'Eclairage coordinates of (0.145, 0.052), closely approaching the BT.2020 blue standard.