Multi-Resonance Induced Thermally Activated Delayed Fluorophores for Narrowband Green OLEDs.

High-color-purity emissions with small a full-width at half-maximum (FWHM) are an ongoing pursuit for high-resolution displays. Though the flourishment of narrow-band emissive materials with multi-resonance induced thermally activated delayed fluorescence (MR-TADF) in the blue region, such materials have not validated their potential in other color regions. By amplifying the influence of skeleton and peripheral units, a series of highly efficient green-emitting MR-TADF materials are firstly reported. Peripheral units with electron-deficit properties can significantly narrow the energy gap for bathochromic emission without compromising the color fidelity. MR-TADF emitters with photo-luminance quantum yields of above 90 % with FWHMs of ≤25 nm are developed. The corresponding organic light-emitting diodes show maximum external quantum efficiency/ power efficiency of 22.02 %/ 69.82 lm W-1 with excellent long-term stability.