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Effects of donor position and multiple charge transfer pathways in asymmetric pyridyl-sulfonyl TADF emitters

Haykir, Gulcin and Aydemir, Murat and Tekin, Adem and Tekin, Emine and Danos, Andrew and Yuksel, Fatma and Hizal, Gurkan and Monkman, Andrew P. and Turksoy, Figen (2022) 'Effects of donor position and multiple charge transfer pathways in asymmetric pyridyl-sulfonyl TADF emitters.', Materials Today Communications, 31 . p. 103550.


We have designed and synthesized a pair of highly asymmetric D-aA-D′ type pyridyl-sulfonyl based isomers comprising phenothiazine (PTZ) and carbazole (Cz) donor units, which are able to emit thermally activated delayed fluorescence. PTZ-pS4-Py-2Cz and PTZ-mS4-Py-2Cz both possess spatial separation of HOMO/LUMO on the donor and acceptor moieties, resulting in small calculated singlet–triplet energy gaps (~0.25 eV). Both isomers exhibit dual emission, which is attributed to charge transfer states associated with the Cz and PTZ moieties at higher and lower energies, respectively. Photoluminescence quantum yields and time-resolved emission decays show significant differences for the two isomers, with the para- isomer exhibiting more efficient emission and stronger delayed fluorescence than the meta- isomer – in strong contrast to recently reported analogous Cz-Cz D-aA-D isomers. The findings clearly show that the interconversion of triplets via the rISC mechanism is promoted when parallel Cz and PTZ charge transfer states are allowed to interact, explaining the improved performance of the Cz-PTZ materials compared to the previous Cz-Cz ones. Finally, moderate device performance was achieved in warm-yellowish (CIE; 0.41; 0.53 & 0.49; 0.48) non-doped OLEDs, which exhibited 0.5% & 1.9% maximum external quantum efficiencies for the meta- and para- isomers, respectively.

Item Type:Article
Full text:(AM) Accepted Manuscript
Available under License - Creative Commons Attribution Non-commercial No Derivatives 4.0.
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Publisher statement:© 2022. This manuscript version is made available under the CC-BY-NC-ND 4.0 license
Date accepted:12 April 2022
Date deposited:29 June 2022
Date of first online publication:15 April 2022
Date first made open access:15 April 2023

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