Hybrid Multi‐Resonance Molecular Design for Ultra‐Narrow Violet Emission

The development of efficient violet organic light‐emitting diodes (OLEDs) remains challenging due to the intrinsic trade‐off between maintaining a short emission wavelength, achieving high efficiency, and preserving a narrow emission spectrum. Here, we report a hybrid multi‐resonance (MR) thermally activated delayed fluorescence (TADF) emitter, BO‐ o ‐2OICz, obtained by symmetrically fusing rigid indolocarbazole units with a 5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracene‐based boron MR core. This design enhances molecular rigidity, suppresses vibrational relaxation, and preserves the high‐energy MR framework required for narrowband violet emission. Theoretical analyses reveal minimal geometric displacement, low reorganization energy, and reduced Huang–Rhys factors, consistent with the experimentally observed ultranarrow emission spectra. BO‐ o ‐2OICz exhibits a photoluminescence quantum yield exceeding 90% and remarkably narrow full width at half maximum (FWHM) of 14–19 nm in solution and thin films. Violet organic light‐emitting diodes based on BO‐ o ‐2OICz exhibit emission at 418–420 nm with a narrow FWHM of 16–20 nm, excellent color purity (CIE y ≤ 0.022), and external quantum efficiency of up to 10.3%.