Novel Nitrogen‐Free Meta‐Triboron‐Doped PAH via Stepwise Borylations Enables Intrinsic Ultraviolet Thermally Activated Delayed Fluorescence at 378 nm with Narrow FWHM of 8.4 nm/0.073 eV

ABSTRACT The multiple resonance (MR) effect paves a promising pathway for organoboron‐doped polycyclic aromatic hydrocarbons (PAHs) to realize narrowband thermally activated delayed fluorescence (TADF). Nevertheless, such emitters struggle to approach the ultraviolet region, as they generally employ nitrogen atoms as strong electron‐donating centers. While the weak electron‐donating oxygen substitution can lead emission to blueshift, it severely impairs MR characteristics and attenuates TADF performance. To address these challenges, we proposed an innovative strategy by installing two boron—oxygen covalent bonds on the DOBNA framework, enabling enhanced MR characteristics, improved molecular rigidity, and tailored electronic structure in the new meta‐triboron‐doped PAH skeleton. The corresponding emitters were successfully synthesized using stepwise borylations, exhibiting intrinsic ultraviolet photoluminescence at 378 nm, with record‐narrow full width at half maxima (FWHM) of 8.4 nm/0.073 eV, alongside pronounced TADF behaviors. In organic light‐emitting diodes (OLEDs), ultraviolet electroluminescence at 383 nm with an impressive FWHM of 15.4 nm/0.135 eV was realized, representing one of the narrowest among ultraviolet OLEDs and even narrower than most advanced visible OLEDs. The corresponding external quantum efficiencies exceeded 8%. This work pioneers establishes a universal design paradigm for developing narrowband ultraviolet TADF emitters, thus opening new avenues for efficient triplet harvesting in the ultraviolet region.