Deep-red to NIR Solution-Processed OLEDs of Donor-Decorated Quinoxaline-based TADF Aggregates

We report the use of an extended -conjugated electron-deficient “pyrazino[2,3-g]quinoxaline (PQ)” as a strong, planar acceptor in a donor-acceptor thermally activated delayed fluorescence emitter design to achieve deep-red to NIR emission. A pair of multi-donor-acceptor (multi-D-A) emitters, 4DMAC-TPPQ and 4PXZ-TPPQ, using PQ as the strong acceptor and dimethylacridine (DMAC) and phenoxazine (PXZ) as strong donors, respectively, emit at 650 and 762 nm in toluene, which is significantly red-shifted in comparison to the parent compound TPPQ (PL = 456 nm). Both compounds show aggregation-induced emission enhancement in THF:water mixtures. Both compounds are TADF as doped films in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) and as neat films. The emission of the neat film is similar to that in toluene with PL of 654 and 770 nm for 4DMAC-TPPQ and 4PXZ-TPPQ, respectively. Solution-processed organic light-emitting diodes (SP-OLEDs) of neat 4DMAC-TPPQ showed electroluminescence (EL) at 685 nm and EQEmax of 0.3%, while the device with 4PXZ-TPPQ emitted at EL of 780 nm and showed an EQEmax of 0.04%. The OLEDs with 4PXZ-TPPQ showed the most red-shifted emission amongst those employing TADF emitters containing a quinoxaline-type acceptor.