Spiro[Acridine-Indoloacridine] Donor Based TADF Emitter with Near-Unity PLQY and Horizontal Dipole Orientation toward High-Efficiency OLEDs with Low Efficiency Roll-Off

Designing thermally activated delayed fluorescence (TADF) emitters with excellent photoluminescence quantum yield (PLQY), preferential horizontal emitting dipole orientation (Theta(//)), and fascinating ability to rapidly utilize both singlet and triplet excitons for radiation is crucial for high-performance organic light-emitting diodes (OLEDs) with both high efficiency and relieved efficiency roll-off. Integrating these advantages into a single TADF emitter is a formidable challenge. In this work, a spiro[acridine-indoloacridine]-based rigid donor, named AIA, is designed to establish a cooperatively long-axis extended and conjugation expanded donor-acceptor type TADF emitter (AIA-TRZ). The proof-of-the-concept emitter simultaneously achieves an excellent PLQY of 99%, a near-unity Theta(//) of 99%, and balanced excited state dynamic parameters. OLEDs based on AIA-TRZ realize remarkable performance with an emission peak at around 480 nm, including doping concentration insensitivity, a maximum external quantum efficiency (EQE(max)) of 37.3%, extremely low efficiency roll-off, and over 20% EQE even at 14000 cd m(-2). A donor of spiro[acridine-indoloacridine] enables a superior D-A type thermally activated delayed fluorescence emitter of AIA-TRZ with near-unity photoluminescence quantum yield and horizontal emitting dipole orientation, as well as fast but balanced kr, kISC, and kRISC rates. The AIA-TRZ-based organic light-emitting diodes achieve excellent performance with a high maximum external quantum efficiency of 37.3% and low efficiency roll-off of 11.2% at 1000 cd center dot m(-2).image