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[Ir(N^N^N)(C^N)L]+: A New Family of Luminophores Combining Tunability and Enhanced Photostability

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journal contribution
posted on 03.02.2014, 00:00 by Danielle N. Chirdon, Wesley J. Transue, Husain N. Kagalwala, Aman Kaur, Andrew B. Maurer, Tomislav Pintauer, Stefan Bernhard
The relatively unexplored luminophore architecture [Ir­(N^N^N)­(C^N)­L]+ (N^N^N = tridentate polypyridyl ligand, C^N = 2-phenylpyridine derivative, and L = monodentate anionic ligand) offers the stability of tridentate polypyridyl coordination along with the tunability of three independently variable ligands. Here, a new family of these luminophores has been prepared based on the previously reported compound [Ir­(tpy)­(ppy)­Cl]+ (tpy = 2,2′:6′,2″-terpyridine and ppy = 2-phenylpyridine). Complexes are obtained as single stereoisomers, and ligand geometry is unambiguously assigned via X-ray crystallography. Electrochemical analysis of the materials reveals facile HOMO modulation through ppy functionalization and alteration of the monodentate ligand’s field strength. Emission reflects similar modulation shifting from orange to greenish-blue upon replacement of chloride with cyanide. Many of the new compounds exhibit impressive room temperature phosphorescence with lifetimes near 3 μs and quantum yields reaching 28.6%. Application of the new luminophores as photosensitizers for photocatalytic hydrogen generation reveals that their photostability in coordinating solvent is enhanced as compared to popular [Ir­(ppy)2(bpy)]+ (bpy = 2,2′-bipyridine) photosensitizers. Yet, the binding of their monodentate ligand emerges as a source of instability during the redox processes of cyclic voltammetry and mass spectrometry. DFT modeling of electronic structure is provided for all compounds to elucidate experimental properties.