Pentacyclic Ladder-Heteraborin Emitters Exhibiting High-Efficiency Blue Thermally Activated Delayed Fluorescence with an Ultrashort Emission Lifetime

As one of the three primary colors, blue is significant
for display
and lighting applications and the development of blue-emitting molecules
with high quantum efficiency, and color purity for organic light-emitting
diodes (OLEDs) remains a key challenge. Herein, a new series of blue
thermally activated delayed fluorescence (TADF) materials featuring
π-extended ladder-oxaborin and thiaborin acceptors has been
developed. Steady-state and time-resolved photophysical measurements
revealed the advantages of the ladder-oxaborin emitter, including
a tiny singlet–triplet energy splitting of 10 meV, an ideal
photoluminescence quantum yield of 100%, and an ultrashort TADF lifetime
of 780 ns. The TADF-OLEDs incorporating the ladder-oxaborin (deep-blue)
and thiaborin (sky-blue) emitters achieved significantly high external
electroluminescence quantum efficiencies of up to 20.1% and 25.9%,
respectively, accompanied by suppressed efficiency roll-offs.