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Issue 13, 2012
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Colour tuning from green to red by substituent effects in phosphorescent tris-cyclometalated iridium(iii) complexes of carbazole-based ligands: synthetic, photophysical, computational and high efficiency OLED studies

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Abstract

Two series of fac-tris-cyclometalated iridium(III) complexes, series 1 from the 2-(carbazol-3′-yl)-pyridine ligands, and series 2 from the isomeric 2-(carbazol-2′-yl)-pyridine ligands, have been characterised. The photoluminescence and electroluminescence from series 2 complexes are red shifted compared to series 1 complexes, due to the increased electron donating ability of the carbazole unit in series 2. The attachment of trifluoromethyl and methoxy substituents to the pyridyl ring in these complexes results in colour tuning of phosphorescence energy maxima over the range 494–637 nm (green to red). These complexes possess predominantly 3MLCT (metal-to-ligand-charge transfer) excited states. DFT/TD-DFT computations correctly predict the phosphorescence emission maxima and show that the HOMOs in these complexes contain mixed iridium and carbazolyl character. The carbazolyl ligand contributions to the excited states increase in series 2 compared to series 1. Complexes of series 1 exhibit high phosphorescence quantum yields whereas complexes of series 2 show lower quantum yields. Solution processed organic light emitting devices (OLEDs) with series 1 complexes using the high triplet poly(9-vinylcarbazole) (PVK) as the host polymer exhibit very high performances of up to 40 cd A−1 and external quantum efficiency of 12%. For series 2 the highest current efficiency is 10.3 cd A−1 and external quantum efficiency of 5.6%.

Graphical abstract: Colour tuning from green to red by substituent effects in phosphorescent tris-cyclometalated iridium(iii) complexes of carbazole-based ligands: synthetic, photophysical, computational and high efficiency OLED studies

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Article information


Submitted
07 Oct 2011
Accepted
10 Feb 2012
First published
22 Feb 2012

J. Mater. Chem., 2012,22, 6419-6428
Article type
Paper

Colour tuning from green to red by substituent effects in phosphorescent tris-cyclometalated iridium(III) complexes of carbazole-based ligands: synthetic, photophysical, computational and high efficiency OLED studies

M. Tavasli, T. N. Moore, Y. Zheng, M. R. Bryce, M. A. Fox, G. C. Griffiths, V. Jankus, H. A. Al-Attar and A. P. Monkman, J. Mater. Chem., 2012, 22, 6419
DOI: 10.1039/C2JM15049B

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