Approaching National Television System Committee Blue Gamut Through Asymmetric Modification of MR‐TADF Material

Abstract An ultrapure deep‐blue multi‐resonance‐induced thermally activated delayed fluorescence (MR‐TADF) material ( DOB2‐DABNA‐C‐NP ) is synthesized as a promising emitter for organic light‐emitting diodes (OLEDs). The emission color is precisely tuned by adopting the asymmetric structure, which is modified from the previously reported symmetric compounds. Notably, the compound exhibits narrowband pure blue emission at 458 nm with a small full width at half maximum (FWHM) of 27 nm. In addition, the large π‐extended structure enables high rate constants for reverse intersystem crossing of 8.0 × 10 5 s −1 . Theoretical calculations for model compounds indicate that the difference in the position of oxygen atoms significantly affects the LUMO energy levels, rationalizing the emission wavelength tuning. The OLED employing DOB2‐DABNA‐C‐NP as an emitter exhibits ultrapure deep‐blue emission at 458 nm with a small FWHM of 23 nm. This corresponds to Commission Internationale d’Éclairage (CIE) coordinates of (0.137, 0.069), which are close to the requirement for blue emitters defined by NTSC and Adobe RGB's standards. The device exhibits excellent external quantum efficiencies of 21.7% at the maximum and 20.8% at 1000 cd m −2 , demonstrating a highly suppressed efficiency roll‐off.