Deep-red to NIR solution-processed OLEDs of donor-decorated quinoxaline-based TADF aggregates†

We report the use of an extended π-conjugated electron-deficient “pyrazino[2,3-g]quinoxaline (PQ)” as a strong, planar acceptor in a donor–acceptor thermally activated delayed fluorescence (TADF) 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 (λ_PL = 456 nm). Both compounds show aggregation-induced emission enhancement in THF:water mixtures. Both compounds exhibit 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 λ_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 (λ_EL) at 685 nm and an EQE_max of 0.3%, while the device with 4PXZ-TPPQ emitted at an λ_EL of 780 nm and showed an EQE_max of 0.04%. The OLEDs with 4PXZ-TPPQ showed the most red-shifted emission amongst those employing TADF emitters containing a quinoxaline-type acceptor.