Highly Efficient C/N‐Fused Architecture for Narrowband Deep‐Blue Thermally Activated Delayed Fluorescence

Emitters with high color purity and small full width at half maximum (FWHM) have attracted considerable attention in recent years. In this work, a novel narrow‐emitting thermally activated delayed fluorescent (TADF) emitter, p‐FLDID, is developed through C/N fusion. The p‐FLDID is developed through core structure modification instead of peripheral substituent engineering. The design approach activates the TADF pathway and regulates emission in the deep‐blue region. The multiresonance (MR) type p‐FLDID emitter exhibits deep‐blue emission with a peak wavelength of 449 nm, FWHM of 26 nm, Stokes shift of 13 nm, and a photoluminescence quantum yield of ≈97%. The rigid structure of p‐FLDID not only restricts the molecular motion of the conjugated backbone structure but also results in a high horizontal emitting dipole orientation of 91%. The fabricated p‐FLDID‐based organic light‐emitting diode exhibits deep blue emission with an external quantum efficiency of 22.0%, a FWHM of 29 nm, and a CIEy of 0.073. The present work demonstrates that high‐efficiency TADF emission with a high‐purity blue color can be realized via C/N fusion. The narrow‐emitting and highly efficient C/N fused blue emitter is developed through basic building block modification using an extended conjugation structure instead of peripheral substituent engineering. The blue organic light‐emitting diode exhibits deep‐blue emission with a high external quantum efficiency of 22.0% and a small full width at half maximum of 29 nm.