ABSTRACT Narrowband multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters are pivotal for wide‐color‐gamut displays, yet they often encounter an inherent trade‐off between emission redshift and spectral broadening. In this study, we present a molecular design strategy that incorporates antiaromatic four‐membered rings into a boron‐ and nitrogen‐embedded MR framework to achieve aromaticity localization. This approach enhances the aromaticity localization within the MR skeleton, effectively suppressing vibrational coupling and narrowing the emission spectrum, while simultaneously extending the π‐conjugation to induce a bathochromic shift—thereby counteracting the typical broadening that accompanies redshift. Relative to the DABNA‐1 parent molecule, the designed emitter exhibits a substantially redshifted emission maximum from 460 to 523 nm, along with a narrowed full‐width at half‐maximum (FWHM) from 27 to 16 nm. The corresponding organic light‐emitting diode (OLED) achieves a narrow FWHM of 21.5 nm with CIE coordinates of (0.26, 0.70), a maximum external quantum efficiency (EQE max ) of 36.1%, and a significantly low efficiency roll‐off. Remarkably, the device demonstrates superior operational stability with an LT90 lifetime of 1469 h at an initial luminance of 1000 cd m −2 . This work establishes a novel paradigm in molecular design for realizing long‐wavelength MR‐TADF emitters that concurrently achieve high color purity and excellent electroluminescence performance.
Liu et al. (Tue,) studied this question.