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.