Azepine Modulation in Thermally Activated Delayed Fluorescence Emitters for OLEDs Achieving Nearly 40% EQE

Thermally activated delayed fluorescence (TADF) emitters play a crucial role in advancing the use of OLED technologies to meet the increasing demands of full-color displays and solid-state lighting. In this work, we present two azepine-pyridine-carbonitrile-based compounds named ISBmPPC and IDBmPPC. Compared to ISBmPPC with a donor iminostilbene (ISB), IDBmPPC with a donor iminodibenzyl (IDB) displays an excellent photoluminescence quantum yield of 95.8%. IDBmPPC with a single bond in a seven-membered nitrogen-containing heterocycle obtains a ΔEST of 0.03 eV, a reverse intersystem crossing rate of 2.85 × 106 s–1, and a horizontal dipole orientation (Θ//) of 85% in the solid state. Consequently, the IDBmPPC-based OLED device achieved a maximum external quantum efficiency of 39.6%, a maximum current efficiency of 130.1 cd A–1, and a maximum power efficiency of 136.2 lm W–1 with a CIE color coordinate of (0.31, 0.57). This IDB-based molecular design is expected to be applicable to other systems for improving OLED performance.