Pentacarbonitrile-based efficient near-infrared thermally activated delayed fluorescence OLEDs via suppressing excited-state structural relaxation†

The design and synthesis of efficient near-infrared (NIR) thermally activated delayed fluorescence (TADF) materials are still under-researched. In order to push the emission of TADF materials into the NIR region, five electron-withdrawing cyano groups were introduced into a TADF emitter (TPA-5CN) in this study to realize an extremely low LUMO energy level, thus achieving an emission peak at 822 nm, the longest emission wavelength of TADFs achieved in toluene thus far. In TPA-5CN, the intramolecular steric hindrance between the CN groups and adjacent C–H bonds resulted in excited-state structural relaxation, which accounted for this extraordinarily long-wavelength emission. Organic light-emitting diode (OLED) based on TPA-5CN exhibited excellent external quantum efficiency (EQE) of 4.52% at 766 nm and 2.56% at 796 nm, which were among the best reported in the literature of the doped NIR TADF OLEDs.