Efficient Ultra‐Narrowband OLEDs Based on Carbazole‐Fused Dual‐Boron Embedded Multi‐Resonance Thermally Activated Delayed Fluorescence Materials

Abstract The development of efficient multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials with ultra‐narrowband emission presents an ongoing challenge. In this work, a carbazole‐fused dual‐boron embedded MR‐TADF framework is proposed, achieving three emitters, CFDBO, CFDBA, and CFDBCz, via one‐shot borylation with very high yields of over 70%. The emitters display ultra‐narrowband blue emission with peaks ranging from 452 to 479 nm and small full width at half maximum (FWHM) values of only 16–18 nm in dilute toluene solutions. Furthermore, the organic light‐emitting diode (OLED) incorporating CFDBO exhibits pure‐blue emission with a peak of 460 nm and Commission International de l'Eclairage coordinates of (0.14, 0.12). Meanwhile, OLEDs incorporating CFDBA/CFDBCz demonstrate remarkable performances with high external quantum efficiencies of 30.9%/32.4% and exceptionally slender FWHM values of 21/22 nm, representing outstanding performances among reported MR‐TADF materials.