Realizing Record‐High Electroluminescence Efficiency of 31.5 % for Red Thermally Activated Delayed Fluorescence Molecules

Tailor‐made red thermally activated delayed fluorescence (TADF) molecules comprised of an electron‐withdrawing pyrazino[2,3‐f][1,10]phenanthroline‐2,3‐dicarbonitrile core and various electron‐donating triarylamines are developed. They can form intramolecular hydrogen‐bonding, which is conducive to improving emission efficiency and promoting horizontal orientation and show near infrared (NIR) emissions (692–710 nm) in neat films and red delayed fluorescence (606–630 nm) with high photoluminescence quantum yields (73–90%) in doped films. They prefer horizontal orientation with large horizontal dipole ratios in films, rendering high optical out‐coupling factors (0.39–0.41). Their non‐doped OLEDs exhibit NIR lights (716–748 nm) with maximum external quantum efficiencies ( η ext,max ) of 1.0–1.9%. And their doped OLEDs radiate red lights (606–648 nm) and achieve record‐beating η ext,max of up to 31.5%. These new red TADF materials should have great potentials in display and lighting devices.