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
Date
2012
Authors
Moore, Tom N.
Zheng, Yonghao
Bryce, Martin R.
Fox, Mark A.
Griffiths, Gareth C.
Jankus, Vygintas
Al-Attar, Hameed A.
Monkman, Andrew P.
Journal Title
Journal ISSN
Volume Title
Publisher
Royal Soc Chemistry
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 (MLCT)-M-3 (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%.
Description
Keywords
Chemistry, Materials science, Light-emitting-diodes, Density-functional theory, Electroluminescent properties, Ir(III) complexes, Electrochemical properties, 9-arylcarbazole moieties, State properties, III complexes, Emission, Devices, Charge transfer, Computational efficiency, Excited states, Iridium, Ligands, Light emission, Light emitting diodes, Phosphorescence, Polycyclic aromatic hydrocarbons, Pyridine, Quantum efficiency, Quantum yield, Carbazole units, Carbazolyl, Current efficiency, Electron-donating ability, Emission maxima, External quantum efficiency, Host polymers, Iridium complex, Methoxy, Organic light-emitting devices, Phosphorescence quantum yield, Photophysical, Poly(9-vinylcarbazole), Pyridine ligands, Pyridyl rings, Red-shifted, Solution-processed, Substituent effect, Trifluoromethyl, Iridium compounds
Citation
Tavaslı, M. vd. (2012). "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". Journal of Materials Chemistry, 22(13), 6419-6428.