Creating Concentration-Insensitive TADF Luminogens With Spiro-Fused Xanthone Acceptors for Highly Efficient OLEDs

Robust thermally activated delayed fluorescence (TADF) materials have shown promising applications as emitters and sensitizers for next-generation organic light-emitting diodes (OLEDs). However, most TADF materials have to be dispersed in host matrices at precisely low concentrations to prevent serious emission quenching and exciton annihilation, which is unfavorable in the OLED industry. Herein, four tailored TADF luminogens built with spiro-fused xanthone acceptors and acridine-based spiro donors are developed. Thanks to the rigid and bulky donor and acceptors, these new TADF luminogens hold fast reverse intersystem crossing process and emit strong cyan to green light with high quantum yields of up to 91% and 99% in neat and doped films, respectively. They have balanced bipolar charge transport ability and prefer horizontal dipole orientation. The non-doped OLEDs using them as emitters show an excellent external quantum efficiency (EQE) of 30.6%, with ultra-small roll-offs. They enjoy concentration insensitivity in doped OLEDs, and the EQEs stay stable (29.1%‒36.8%) in various concentrations (10‒90 wt%) with very small roll-offs. Finally, they can serve as efficient sensitizers for multi-resonance emitters in narrow-spectrum OLEDs, providing impressive EQEs of 41.0% with suppressed roll-offs. This work reveals an applicable molecular design strategy of TADF materials for high-performance OLEDs.