Harnessing Antiaromatic Perturbation in Multiple‑Resonance TADF Emitter for Simultaneous Bathochromic Shift and Spectral Narrowing

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.