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Issue 27, 2012
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Dinuclear iridium(III) complexes of cyclometalated fluorenylpyridine ligands as phosphorescent dopants for efficient solution-processed OLEDs

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Abstract

Phosphorescent cyclometalated dinuclear iridium(III) complexes of fluorenylpyridine ligands bridged by bis(μ-Cl) and bis(μ-NCO) units have been synthesised and characterised by NMR, UV-vis absorption and emission spectroscopy, cyclic voltammetry, spectroelectrochemistry and X-ray diffraction. The complexes display green luminescence in solution from mixed 3π–π*/3MLCT (metal-to-ligand-charge transfer) states in the range of λmax 542–552 nm. The solution PL quantum yields of 21–41% are remarkably high for diiridium complexes. Cyclic voltammetric and UV-visible spectroelectrochemical studies establish that the mixed valence cations are stable with the two Ir3+/Ir4+ centres interacting strongly. DFT/TD-DFT calculations provide further insights into the electronic and photophysical properties of the complexes, with good agreement between computed and experimental data. Solution-processed organic light emitting devices (OLEDs) using the diiridium complexes as the emissive dopants in poly(9-vinylcarbazole) (PVK) host polymer exhibit performances of up to 12 cd A−1 and external quantum efficiencies of up to 4%. The device architecture is: ITO/PEDOT:PSS/PVK–complex (5 wt%)–PBD (40 wt%)/Ba/Al. These electroluminescence efficiency values are unusually high for dinuclear metal complexes and confirm that dinuclear iridium complexes are suitable phosphors for OLEDs using simple device architectures. Analogous mononuclear fac-Ir(III) complexes of fluorenylpyridine ligands are reported for comparison. They have PL quantum yields of 30–43%, device performances of up to 26 cd A−1 and external quantum efficiencies of up to 8.6%.

Graphical abstract: Dinuclear iridium(iii) complexes of cyclometalated fluorenylpyridine ligands as phosphorescent dopants for efficient solution-processed OLEDs

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Publication details

The article was received on 23 Feb 2012, accepted on 17 May 2012, published on 01 Jun 2012 and first published online on 01 Jun 2012


Article type: Paper
DOI: 10.1039/C2JM31143G
Citation: J. Mater. Chem., 2012,22, 13529-13540
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    Dinuclear iridium(III) complexes of cyclometalated fluorenylpyridine ligands as phosphorescent dopants for efficient solution-processed OLEDs

    A. M'hamedi, A. S. Batsanov, M. A. Fox, M. R. Bryce, K. Abdullah, H. A. Al-Attar and A. P. Monkman, J. Mater. Chem., 2012, 22, 13529
    DOI: 10.1039/C2JM31143G

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