An Ideal Molecular Construction Strategy for Ultra‐Narrow‐Band Deep‐Blue Emitters: Balancing Bathochromic‐Shift Emission, Spectral Narrowing, and Aggregation Suppression

Abstract Narrowband emissive multiple resonance (MR) emitters promise high efficiency and stability in deep‐blue organic light‐emitting diodes (OLEDs). However, the construction of ideal ultra‐narrow‐band deep‐blue MR emitters still faces formidable challenges, especially in balancing bathochromic‐shift emission, spectral narrowing, and aggregation suppression. Here, DICz is chosen, which possesses the smallest full‐width‐at‐half‐maximum (FWHM) in MR structures, as the core and solved the above issue by tuning its peripheral substitution sites. The 1‐substituted molecule Cz‐DICz is able to show a bright deep‐blue emission with a peak at 457 nm, an extremely small FWHM of 14 nm, and a CIE coordinate of (0.14, 0.08) in solution. The corresponding OLEDs exhibit high maximum external quantum efficiencies of 22.1%–25.6% and identical small FWHMs of 18 nm over the practical mass‐production concentration range (1–4 wt.%). To the best of the knowledge, 14 and 18 nm are currently the smallest FWHM values for deep‐blue MR emitters with similar emission maxima under photoluminescence and electroluminescence conditions, respectively. These discoveries will help drive the development of high‐performance narrowband deep‐blue emitters and bring about a revolution in OLED industry.