Isobenzofuranone- and Chromone-Based Blue Delayed Fluorescence Emitters with Low Efficiency Roll-Off in Organic Light-Emitting Diodes

Significant efforts have been devoted to the development of novel efficient blue-emitting molecules for organic light-emitting diode (OLED) applications. Blue organic emitters exhibiting thermally activated delayed fluorescence (TADF) have the potential to achieve ∼100% internal electroluminescence quantum efficiency in OLEDs. In this paper, we report a promising molecular design strategy for obtaining appropriate high singlet and triplet excited energies, short exciton lifetimes, and high quantum efficiencies in blue TADF emitters. We introduce isobenzofuranone and chromone containing a cyclic ketone or lactone moiety as effective acceptor building units to construct donor-acceptor TADF emitters. Owing to their small singlet-triplet energy splitting, properly contracted π-conjugation, and weakened intramolecular charge-transfer character, these new emitters display strong blue TADF emissions with high photoluminescence quantum yields (53-92%) and notably short TADF emission lifetimes (2.8-4.3 μs) in thin films. Blue TADF-OLEDs utilizing these emitters exhibit external electroluminescence quantum efficiencies of up to 16.2% and extremely low efficiency roll-off even at practical high luminance. The current findings open new avenues for designing practically usable high-performance blue TADF emitters with simple molecular structures.