Revealing Design Rules for Bathochromic Narrowband Emission in ICz‐Based MR‐TADF Emitters via Data‐Driven Discovery

ABSTRACT Indolo[3,2,1‐ jk ]carbazole (ICz)‐based multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters exhibit promising high color purity emission. However, the lack of generalizable structural guidelines for suppressing spectral broadening associated with bathochromic shifted emission realized by conjugation extension has limited the full‐color emission from ICz emitter, particularly in the red region. In this work, we employed molecular generation to systematically explore ICz emitters, subsequently implemented interpretable machine learning (IML) to establish quantitative structure‐property relationships for wavelength and full width at half maximum (FWHM). Assisted by IML, two general structural patterns, para‐oriented N incorporation for red‐shifted emission and ring fusion across the C4‐C5 bond for spectral narrowing were identified. Electronic structure analyses revealed that these patterns enhance the non‐bonding orbital contribution of ICz core, thereby reducing the HOMO‐LUMO gap and suppressing electron‐vibronic coupling. Guided by both principles, we maintained narrowband emission while precisely tuning the emission color, dramatically increasing the success rate for target emission wavelength from 59% to 95% and reducing the proportion of broadband emission molecules by 80%. The extracted rules further guided manually crafting deep‐red emitter achieving CIE coordinates of (0.70, 0.30) with ultranarrow FWHM of 22.5 nm centered at 626 nm.