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

Abstract 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 10 H ‐phenoxazine (PXZ) and 7 H ‐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 a 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 a sensitizer. The PXZ−R−BN‐based sensitized OLEDs achieve a maximum external quantum efficiency (EQE max ) of nearly 30 % with an emission band at 693 nm, and exceptional long operational stability with an LT 97 (time to 97 % of the initial luminance) value of 39084 h at an initial radiance of 1000 mW sr −1 m −2 . The BCz−R−BN‐based OLEDs reach EQE max values of 24.2 % with an emission band at 713 nm, which sets a record value for NIR OLEDs with emission bands beyond 700 nm.