AbstractRationally tuning the emission position and narrowing the full width at half‐maximum (FWHM) of an emitter is of great importance for many applications. By synergistically improving rigidity, strengthening the resonant strength, inhibiting molecular bending and rocking, and destabilizing the HOMO energy level, a deep‐blue emitter (CZ2CO) with a peak wavelength of 440 nm and an ultranarrow spectral FWHM of 16 nm (0.10 eV) was developed via intramolecular cyclization in a carbonyl/N resonant core (QAO). The dominant υ_0‐0transition character of CZ2CO gives a Commission Internationale de I’Éclairage coordinates (CIE) of (0.144, 0.042), nicely complying with the BT.2020 standard. Moreover, a hyper‐fluorescent device based on CZ2CO shows a high maximum external quantum efficiency (EQE_max) of 25.6 % and maintains an EQE of 22.4 % at a practical brightness of 1000 cd m⁻².