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Solution, structural and photophysical aspects of substituent effects in the N^N ligand in [Ir(C^N) 2 (N^N)] + complexes
journal contributionposted on 16.06.2017, 08:58 by Edwin C. Constable, Catherine E. Housecroft, Peter Kopecky, Colin J. Martin, Iain WrightIain Wright, Jennifer A. Zampese, Henk J. Bolink, Antonio Pertegas
The syntheses and properties of a series of eleven new [Ir(ppy) 2(N^N)][PF6] complexes (Hppy = 2-phenylpyridine) are reported. The N^N ligands are based on 2,2-bipyridine (bpy), substituted in the 6- or 5-positions with groups that are structurally and electronically diverse. All but two of the N^N ligands incorporate an aromatic ring, designed to facilitate intra-cation face-to-face π-interactions between the N^N and one [ppy]- ligand. Within the set of ligands, 6-(3-tolyl)-2,2′- bipyridine (5), 4,6-bis(4-nitrophenyl)-2,2′-bipyridine (9), and 4,6-bis(3,4,5-trimethoxyphenyl)-2,2′-bipyridine (10) are new and their characterization includes single crystal structures of 9, and two polymorphs of 10. A representative [Ir(ppy)2(N^O)]+ complex is also described. We report solution NMR spectroscopic, photophysical and electrochemical properties of the complexes, as well as representative solid-state structural data. The solution 1H NMR spectroscopic data illustrate different dynamic processes involving the substituents attached to the bpy domain in the ligands. In degassed MeCN and at room temperature, the [Ir(ppy)2(N^N)][PF6] complexes are orange emitters with λemmax in the range 575 to 608 nm; however, quantum yields are very low. The most promising complexes were evaluated in light-emitting electrochemical cells leading to bright and stable devices with rather good external quantum efficiencies. © 2013 The Royal Society of Chemistry.
We thank the European Research Council (Advanced Grant 267816 LiLo), the Swiss National Science Foundation, and the University of Basel for financial support, the Spanish Ministry of Economy and Competitiveness (MINECO) (MAT2011-24594, CTQ2009-08790 and Consolider-Ingenio CSD2007-00010), the Generalitat Valenciana (PROMETEO/2012/053), and the European Union (CELLO, STRP 248043; https://www.cello-project.eu/) for financial support.