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.