The influence of nitrogen doping of the acceptor in orange–red thermally activated delayed fluorescence emitters and OLEDs
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Nitrogen-containing polycyclic aromatic hydrocarbons (N-PAH) have been widely used as deep lowest unoccupied molecular orbital (LUMO) acceptors in donor-acceptor (D-A) red thermally activated delayed fluorescent (TADF) emitters and their use in organic light-emitting diodes. However, most of the studies have focused disparately on donor/acceptor combinations to yield efficient emitters, while it is rare that there is a methodological study to investigate the influence of the nitrogen (N) doping ratios on the ground and excited states of PAH acceptors. Here, we report a family of four different N-PAH acceptors containing different numbers of nitrogen atoms within the N-PAH and their use in D-A TADF emitters, DMACBP, DMACPyBP, DMACBPN and DMACPyBPN, when coupled to the same donor, 9,9-dimethyl-9,10-dihydroacridine (DMAC). As the nitrogen content in the acceptor increases the LUMO becomes progressively more stabilized while the singlet-triplet energy gap (ΔEST) decreases and the rate constant for reverse intersystem crossing (kRISC) increases. In particular, introducing nitrogen at the 10-position of the dibenzo[a,c]phenazine (BP) leads to a more than ten-fold enhancement in kRISC in DMACPyBP and DMACPyBPN compared to DMACBP and DMACBPN. Among the OLEDs with all four emitters that with DMACBPN demonstrates the highest EQEmax of 19.4% at an emission peak of 588 nm. while the deepest red emitting device employed DMACPyBPN (λEL = 640 nm) with an EQEmax of 5.4%.
Si , C , Hu , Y-N , Sun , D , Wang , K , Zhang , X & Zysman-Colman , E 2023 , ' The influence of nitrogen doping of the acceptor in orange–red thermally activated delayed fluorescence emitters and OLEDs ' , Journal of Materials Chemistry C , vol. Advance article . https://doi.org/10.1039/D3TC02352D
Journal of Materials Chemistry C
Copyright © 2023 The Author(s). Open Access. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
DescriptionFunding: C. Si thanks the China Scholarship Council (201806890001). D.S acknowledges support from the Royal Academy of Engineering Enterprise Fellowship (EF2122-13106). The St Andrews team thanks EPSRC for financial support (EP/P010482/1). X.-H. Zhang acknowledges support from the National Natural Science Foundation of China (Grant Nos. 52130304, 51821002), Suzhou Key Laboratory of Functional Nano & Soft Materials, Collaborative Innovation Center of Suzhou Nano Science & Technology, the 111 Project.
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