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Intramolecular Pi-Pi Interactions with a Chiral Auxiliary Ligand Control Diastereoselectivity in a Cyclometalated Ir(III) Complex

Congrave, Daniel G.; Batsanov, Andrei S.; Du, Mingxu; Liu, Yu; Zhu, Dongxia; Bryce, Martin R.

Intramolecular Pi-Pi Interactions with a Chiral Auxiliary Ligand Control Diastereoselectivity in a Cyclometalated Ir(III) Complex Thumbnail


Authors

Daniel G. Congrave

Mingxu Du

Yu Liu

Dongxia Zhu



Abstract

The application of a chiral auxiliary ligand to control the diastereoselectivity in the synthesis of a cyclometalated iridium(III) complex is presented. The diastereomeric iridium(III) complexes 1a and 1b are reported, in which a phenoxyoxazoline auxiliary ligand incorporates a chiral center functionalized with a pendant pentafluorophenyl group. The diastereomers were readily separated, and their structural, electrochemical and photophysical properties are discussed. Solution-state NMR data and X-ray crystal structures establish that the pentafluorophenyl group engages in intramolecular π–π interactions. The X-ray analysis reveals that the two diastereomers display very different modes of intramolecular stacking. The variable-temperature 19F NMR data indicate that rotation of the pendant pentafluorophenyl rings in 1b and 1a is a temperature-dependent process and that there is a smaller energy barrier to rotation in 1b in comparison to 1a. This correlates with variable-temperature photoluminescence data, which show that upon heating the integrated emission intensity is reduced substantially more for 1b than for 1a, which is ascribed to the enhanced rotation in 1b, providing a more easily populated nonradiative pathway in comparison to 1a. These experimental data are supported by computational calculations. Phosphorescent organic light-emitting devices (PhOLEDs) using 1a as the dopant complex give blue-green emission with a high maximum external quantum efficiency (EQEmax) of 25.8% (at ca. 270 cd m–2) and with a low efficiency roll-off to 24.9% at 1000 cd m–2. Our results extend the scope of ligand design for cyclometalated iridium complexes which possess interesting structural and emission properties.

Citation

Congrave, D. G., Batsanov, A. S., Du, M., Liu, Y., Zhu, D., & Bryce, M. R. (2018). Intramolecular Pi-Pi Interactions with a Chiral Auxiliary Ligand Control Diastereoselectivity in a Cyclometalated Ir(III) Complex. Inorganic Chemistry, 57(20), 12836-12849. https://doi.org/10.1021/acs.inorgchem.8b02034

Journal Article Type Article
Online Publication Date Sep 26, 2018
Publication Date Oct 15, 2018
Deposit Date Sep 25, 2018
Publicly Available Date Sep 26, 2019
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 57
Issue 20
Pages 12836-12849
DOI https://doi.org/10.1021/acs.inorgchem.8b02034

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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.8b02034.





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