Highly Efficient Near-Infrared Thermally Activated Delayed Fluorescent Emitters in Non-Doped Electroluminescent...

Constructing organic near-infrared (NIR) luminescent materials to confront the formidable barrier of "energy gap law" remains challenging. Herein, two NIR thermally activated delayed fluorescence (TADF) molecules named T-β-IQD and TIQD were developed by connecting N,N-diphenylnaphthalen-2-amine and triphenylamine with a novel electron withdrawing unit 6-(4-(tert-butyl)phenyl)-6H-indolo[2,3-b]quinoxaline-2,3-dicarbonitrile. It is confirmed NIR-TADF emitters concurrent with aggregation-induced emission effect, J-aggregate with intra- and intermolecular CN⋅⋅⋅H-C and C-H⋅⋅⋅π interactions, and large center-to-center distance in solid states can boost the emissive efficiencies both in thin films and non-doped organic light-emitting diodes (OLEDs). Consequently, the T-β-IQD-based non-doped NIR-OLED achieved the maximum external quantum efficiency (EQE_max ) of 9.44 % with emission peak at 711 nm, which is one of the highest efficiencies reported to date for non-doped NIR-OLEDs.