Aggregation-Induced Delayed Fluorescence Luminogens with Accelerated Reverse Intersystem Crossing for High-Performance OLEDs

A fast
reverse intersystem crossing (RISC) is of high importance
for delayed fluorescence emitters in terms of increasing exciton utilization
and suppressing efficiency roll-off. Herein, new robust luminogens
comprised of carbonyl, phenoxazine, and chlorine-substituted carbazole
derivatives are synthesized and characterized. They have distinct
aggregation-induced delayed fluorescence (AIDF) features and exhibit
high photoluminescence efficiencies and short delayed fluorescence
lifetimes in neat films. The RISC is conspicuously accelerated because
of their tiny singlet–triplet energy splitting and greatly
enhanced spin–orbit coupling by heavy atom effect in neat films.
They can function efficiently as light-emitting layers in nondoped
OLEDs, providing excellent maximum electroluminescence (EL) efficiencies
of 20.4–21.7%, and can also perform outstandingly in doped
OLEDs in a wide doping concentration range (5–90 wt %), affording
impressive EL efficiencies of up to 100.1 cd A–1, 104.8 lm W–1, and 29.1%, with small efficiency
roll-off. These findings demonstrate the AIDF luminogens with fast
RISC are promising candidates to fulfill various demands of production
and application of OLEDs.