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Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands

Benjamin, Helen; Zheng, Yonghao; Kozhevnikov, Valery N.; Siddle, Jamie S.; O'Driscoll, Luke J.; Fox, Mark A.; Batsanov, Andrei S.; Griffiths, Gareth C.; Dias, Fernando B.; Monkman, Andrew P.; Bryce, Martin R.

Authors

Helen Benjamin

Yonghao Zheng

Valery N. Kozhevnikov

Jamie S. Siddle

Gareth C. Griffiths



Abstract

Five new neutral heteroleptic iridium(III) complexes IrL2(pic) (2–6) based on the archetypical blue emitter FIrpic have been synthesised. The cyclometallating ligands L are derived from 2-(2,6-F2-3-pyridyl)-4-mesitylpyridine (7), 2-(3-cyano-2,6-F2-phenyl)-4-mesitylpyridine (8), 2-(2,6-F2-phenyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (9), 2-(2,6-F2-3-pyridyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (10) and 2-(3-cyano-2,6-F2-phenyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (11) for complexes 2, 3, 4, 5 and 6, respectively. The carbazole-functionalised ligands 9–11 show weak thermally activated delayed fluorescence (TADF) in solution. Complexes 5 and 6 reveal dual emission in polar solvents. A broad charge transfer (CT) band appears and increases in intensity relative to the higher energy emission band as solvent polarity is increased. The dual emission occurs when the energy of the ligand 3CT state is comparable to that of the 3MLCT state of the complex, resulting in fast interconversion between the two. Assignment of the ligand TADF and dual emission properties is supported by hybrid density functional theory (DFT) and time dependent DFT (TD-DFT) calculations. Phosphorescent organic light emitting devices (PhOLEDs) have been fabricated using these complexes as sky-blue emitters, and their performance is compared to devices using FIrpic and the previously reported complex IrL2(pic) 1 (L from the 2-(2,6-F2-phenyl)-4-mesitylpyridine ligand). For identical device structures, the device containing the carbazole complex 4 performs best out of the seven complexes. The dual emission observed in solution for complexes 5 and 6 is not observed in their devices.

Citation

Benjamin, H., Zheng, Y., Kozhevnikov, V. N., Siddle, J. S., O'Driscoll, L. J., Fox, M. A., …Bryce, M. R. (2020). Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands. Dalton Transactions, 49(7), 2190-2208. https://doi.org/10.1039/c9dt04672k

Journal Article Type Article
Acceptance Date Jan 23, 2020
Online Publication Date Jan 31, 2020
Publication Date Feb 21, 2020
Deposit Date Mar 5, 2020
Publicly Available Date Jan 31, 2021
Journal Dalton Transactions
Print ISSN 1477-9226
Electronic ISSN 1477-9234
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 49
Issue 7
Pages 2190-2208
DOI https://doi.org/10.1039/c9dt04672k

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