Interrupted intramolecular donor-acceptor interaction compensated by strong through-space electronic coupling for highly efficient near-infrared TADF with emission over 800 nm

Abstract

Near-infrared (NIR) organic emitters with emission wavelength from 700 to 900 nm show promising application in phototherapy, bioimaging and night vision products. The traditional fluorescent compounds composed of strong donor (D) and acceptor (A) units can readily achieve NIR emission via the extensive conjugation over the molecular skeleton. However, the development of NIR thermally activated delayed fluorescence (TADF) is still an unaddressed issue mainly due to the limited conjugation between D and A within TADF molecules. Here, the strategy is to introduce strong D/A fragments into the molecular skeleton and to incorporate the strong through-space electronic coupling between TADF molecules simultaneously. With this strategy, we demonstrate an unprecedented NIR TADF material (AQTC-DTPA) with emission over 800 nm. TADF OLEDs based on AQTC-DTPA show the record-high maximum External quantum efficiencies (EQE) of 0.51%/0.41%/0.30%/0.23% with Electroluminescence (EL) peak wavelength at 810/828/852/894 nm, respectively.