Construction of Efficient Deep-Red/Near-Infrared Emitter Based on a Large π-Conjugated Acceptor and Delayed Fluorescence OLEDs with External Quantum Efficiency of over 20%

Organic light-emitting materials with thermally activated delayed fluorescence (TADF) are promising for promoting the efficiency of organic light emitting diodes (OLEDs) without any precious metals. However, the device performance of the deep-red/near-infrared (DR/NIR) TADF-OLEDs remains backward compared with that of blue, green, and orange-red TADF-OLEDs. In this contribution, a donor acceptor type TADF emitter, 2-(tert-butyl)-6-(4-(diphenylamino)phenyl)phenanthro [4,5-abc]phenazine-11,12-dicarbonitrile, namely, TPA-PPDCN, containing a large rigid phenanthro[4,5-abc]phenazine-11,12-dicarbonitrile as an acceptor unit and a triphenylamine (TPA) as a donor moiety, is designed and synthesized. The compound exhibits excellent thermal stability, small singlet-triplet energy split and a strong DR/NIR emission with the photoluminescence quantum yields of 73-87% in doped thin films. More importantly, highly efficient DR and NIR OLEDs with emission peaks at 664 and 692 nm and the maximum external quantum efficiencies of 20.2 and 16.4%, respectively, have been achieved, which represent the highest' device performance among the reported DR/NIR TADF OLEDs.