Narrowband Near‐Infrared Multiple‐Resonance Thermally Activated Delayed Fluorescence Emitters towards High‐Performance and Stable Organic Light‐Emitting Diodes

Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) materials are highly coveted for their high efficiency and narrowband emission in organic light‐emitting diodes (OLEDs). Nevertheless, the development of near‐infrared (NIR) MR‐TADF emitters remains a formidable challenge. In this study, we design two new NIR MR‐TADF emitters, PXZ‐R‐BN and BCz‐R‐BN, by embedding 10H‐phenoxazine (PXZ) and 7H‐dibenzo[c,g]carbazole (BCz) fragments to increase the electron‐donating ability or extending π‐conjugation on the framework of para‐boron fusing polycyclic aromatic hydrocarbons (PAHs). Both compounds emit in the NIR region, with full‐width at half‐maximum (FWHM) of 49 nm (0.13 eV) for PXZ‐R‐BN and 43 nm (0.11 eV) for BCz‐R‐BN in toluene. To sensitize the two NIR MR‐TADF emitters in OLEDs, a new platinum complex, Pt‐1, is designed as sensitizer. The PXZ‐R‐BN‐based sensitized OLEDs achieve a maximum external quantum efficiency (EQEmax) of nearly 30% with emission peak at 693 nm, and exceptional long operational stability with LT97 (time to 97% of the initial luminance) of 39084 h at initial radiance of 1000 mW sr‐1 m‐2. The BCz‐R‐BN‐based OLEDs acquire EQEmax of 24.2% with emission peak at 713 nm, which sets a record value for NIR OLEDs with emission peaks beyond 700 nm.