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Rationally 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 0-0 transition 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 À 2 .

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High-performance deep-blue emitters with external quantum efficiencies (EQEs) exceeding 5% are still scarce in organic light-emitting diodes (OLEDs). In this work, by introducing a [ 1,2,4]triazolo [1,5-a]p yridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescentm aterials, PTPTPA and PTPTPA,w ere obtained. Systematic photophysical analysis showed that the TP block is suitable for constructingh ybridized local and charge-transfer( HLCT) emitters. Its moderate electron-withdrawing ability and rigid planar structure can enhancet he CT component while ensuring color purity.I na ddition, compared with PTPTPA,t he additional phenyl ring of PTPBPTAn ot only increased the oscillator strength,b ut also decreased the Stokes shift. TDDFT calculations pointed out facile reverse intersystem crossing processes in PTPTPA from high-lying triplet states to the singlet excited state. An ondoped device based on PTPTPA as emitter showed impressive performance with EQE max of 7.11% and CIE coordinates of (0.15, 0.09). At the same time, it was also an efficient host for yellow and red phosphorescent OLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dyes into PTPTPA,awhite OLED with ah igh EQE of 23.85 %w as achieved. The successful design of PTPTPA not only provideda no ptimization choice for OLED emitters, but also demonstrated thee mpirical rules for the design of multifunctional deep-blue emitters.

Rationally 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 υ0‐0 transition 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 (EQEmax) of 25.6 % and maintains an EQE of 22.4 % at a practical brightness of 1000 cd m−2.