Intramolecular π Stacking in Cationic Iridium(III) Complexes with Phenyl-Functionalized Cyclometalated Ligands: Synthesis, Structure, Photophysical Properties, and Theoretical Studies

Li, Peng; Shan, Guo-Gang; Cao, Hong-Tao; Zhu, Dong-Xia; Su, Zhong-Min; Jitchati, Rukkiat; Bryce, Martin R.

Abstract

The syntheses of two new heteroleptic cationic iridium complexes containing 2,6-diphenylpyridine (Hdppy) and 2,4,6-triphenylpyridine (Htppy) as the cyclometalated ligands, namely, [Ir(dppy)2phen]PF6 (1, phen = 1,10-phenanthroline) and [Ir(tppy)2phen]PF6 (2), are described. The X-ray crystal structure of 2 reveals a distorted octahedral geometry around the Ir center and close intramolecular face-to-face π–π stacking interactions between the pendant phenyl rings at the 2-position of the cyclometalated ligands and the NN ancillary ligand. This represents a new π–π stacking mode in charged Ir complexes. Complexes 1 and 2 are green photoemitters: their photophysical and electrochemical properties are interpreted with the assistance of density functional theory (DFT) calculations. These calculations also establish that the observed intramolecular interactions cannot effectively prevent the lengthening of the Ir–N bonds of the complexes in their metal-centered (3MC) states. Complexes 1 and 2 do not emit light in light-emitting electrochemical cells (LECs) under conditions in which the model compound [Ir(ppy)2phen]PF6 (3) emits strongly. This is explained by degradation reactions of the 3MC state of 1 and 2 under the applied bias during LEC operation facilitated by the enhanced distortions in the geometry of the complexes. These observations have important implications for the future design of complexes for LEC applications.

Citation

Li, P., Shan, G., Cao, H., Zhu, D., Su, Z., Jitchati, R., & Bryce, M. R. (2014). Intramolecular π Stacking in Cationic Iridium(III) Complexes with Phenyl-Functionalized Cyclometalated Ligands: Synthesis, Structure, Photophysical Properties, and Theoretical Studies. European Journal of Inorganic Chemistry, 2014(14), 2376-2382. https://doi.org/10.1002/ejic.201400007

• Journal Article Type: Article
• Publication Date: May 1, 2014
• Deposit Date: Nov 24, 2014
• Publicly Available Date: Nov 26, 2014
• Journal: European Journal of Inorganic Chemistry
• Print ISSN: 1434-1948
• Electronic ISSN: 1099-0682
• Publisher: Wiley-VCH Verlag
• Peer Reviewed: Peer Reviewed
• Volume: 2014
• Issue: 14
• Pages: 2376-2382
• DOI: https://doi.org/10.1002/ejic.201400007
• Keywords: Iridium, Luminescence, Photophysics, Density functional calculations, Light-emitting cells.
• Public URL: https://durham-repository.worktribe.com/output/1449942