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.