Stepwise Planarizing Geometries of D–A Type Red Thermally Activated Delayed Fluorescence Molecules in Condensed States Toward High-Efficiency Red/NIR OLEDs

Abstract

Quasiplanar donor–acceptor (D–A) thermally activated delayed fluorescence (TADF) molecules are appealing candidates for efficient red/near-infrared (NIR) emitters but have not been realized. Herein, for the first time, a stepwise approach to achieve this goal via a spiro-locked C─C covalent bond linking strategy combined with the subtle management of intermolecular C─H···CN noncovalent bonds in condensed states is presented. This synergetic effect enables the newly developed molecule, DCN-SAC, to not only attain nearly unity photoluminescence quantum yield, with a horizontal dipole ratio of up to 89% at 5 wt% doped conditions but also achieve a quasiplanar configuration with high-exciton-harvesting J-aggregates under neat condensed conditions. The optimized organic light-emitting diode (OLED) using DCN-SAC as the dopant furnishes a topmost external quantum efficiency (EQE) of 38.7% at 631 nm among all red OLEDs based on TADF materials. More importantly, a DCN-SAC-based nondoped OLED affords a remarkable EQE of 12.6% with an emission peak at 730 nm, which sets a record-breaking value among all previously reported nondoped TADF devices in the similar emission region. These findings reveal the effectiveness and great potential of stepwise planarity, presenting a new paradigm for developing high-efficiency red/NIR TADF OLEDs.