Stepwise Planarizing Geometries of D–A Type Red Thermally Activated Delayed Fluorescence Molecules in Condensed States Toward High‐Efficiency Red/NIR OLEDs
Hui Wang, Sen Lin, Jia‐Xiong Chen, Xiao‐Yao Hao, Xiao‐Chun Fan, Yi‐Zhong Shi, Jia Yu, Xiankai Chen, Kai Wang, Xiaohong Zhang
Abstract
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.