Ultra‐Narrowband Pure‐Red Multi‐resonance Emitters Enabled by Modular Synthesis via Chlorine‐Oriented Double Borylation and Peripheral Extension

Narrowband pure‐red emitters are essential for ultrahigh‐definition organic light‐emitting diode (OLED) displays. However, organic emitters with a full width at half maximum (FWHM) < 0.1 eV and CIE‐x > 0.67 (NTSC red standard) remain rare, as redshifted emission often causes spectral broadening and increased nonradiative decay. Herein, leveraging a facile chlorine‐oriented direct double borylation strategy that offers high synthetic accessibility and structural expandability, two pure‐red fluorophores with near‐unity photoluminescence quantum yields and unprecedentedly narrow emission are constructed through nearly coplanar decoration of peripheral triazine electron‐acceptors on a para‐boron‐substituted naphthalene multiresonance core. By simultaneously stabilizing the emissive state and suppressing high‐frequency vibrations, these emitters achieve extremely narrow emission (FWHM = 0.078 eV) and CIE coordinates of (0.69, 0.31) and (0.70, 0.30) in toluene. The phosphor‐assisted OLED achieves ultranarrow red emission centered at 629 nm (FWHM = 0.1 eV, CIE‐x = 0.69), approaching BT.2020 standard, with an external quantum efficiency of 26.6% and a power efficiency of 33.8 lm/W—among the best reported for pure‐red OLEDs. This work presents an efficient design strategy for red emitters that simultaneously achieves high color purity, ultra‐narrowband emission, high efficiency, and synthetic simplicity.