b512081k

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Blue emitting iridium complexes: synthesis, photophysics and phosphorescent devices { Roberta Ragni, a Edward A. Plummer, bc Klemens Brunner, c Johannes W. Hofstraat, c Francesco Babudri, ad Gianluca M. Farinola, a Francesco Naso * ad and Luisa De Cola * b Received 25th August 2005, Accepted 7th December 2005 First published as an Advance Article on the web 6th January 2006 DOI: 10.1039/b512081k Homoleptic Ir(F n ppy) 3 and heteroleptic (F n ppy) 2 Ir(acac) complexes ( n =3 :F 3 ppy = 2-(3 9 ,4 9 ,6 9 -trifluorophenyl)pyridine; n =4 :F 4 ppy = 2-(3 9 ,4 9 ,5 9 ,6 9 -tetrafluorophenyl)pyridine; acac = acetylacetonate) have been synthesized and their spectroscopic properties investigated. The homoleptic complexes exist as two stereoisomers, facial ( fac ) and meridional ( mer ), that have been isolated and fully characterized. Their electrochemical and photophysical properties have been studied both in solution and in the solid state and electroluminescent devices have been fabricated. The emissive layers in devices have been obtained mixing the iridium complexes with a PVK [poly(9-vinylcarbazole)] host matrix, in the presence of the electron carrier Bu-PBD [2-(4- biphenylyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole]. The application of a voltage (5.0–6.5 V) between the electrodes of devices leads to electro-generated blue luminescence which has similar energy to the solution emissions. Interestingly, the stability of the devices made with the homoleptic fluorinated iridium complexes strongly depends on the stereochemistry of these phosphors and high (up to 5.5%) external quantum efficiencies for the fac complexes are measured. Introduction The photophysics of heavy metal complexes and their use as photoactive components in the construction of systems for photonic applications have been extensively studied. 1 In particular, Ru(II), 2 Pt(II), 3 Os(II), 4 Ir(III) 5 complexes with suitable ligands are emissive at room temperature and possess interesting photophysical and redox properties. These facets make them useful materials for the construction of multi- component systems involving energy and/or electron transfer processes. 6 Luminescent ruthenium complexes, mostly bearing bipyridine ligands, have received great attention so far and spectroscopic studies have shown that their luminescence arises from the lowest triplet Metal to Ligand Charge Transfer excited state ( 3 MLCT) that, due to its phosphorescent character, is long living. More recently, great interest has been devoted to heavy metal complexes having higher quantum yields and color tunability, with the aim to obtain phosphorescent materials more suitable for biomedical 7 and optoelectronic 8 applications. In particular, iridium complexes bearing 2-phenylpyridine ligands have the advantage that their emission energy can be finely tuned from blue to red by the peripheral functionalization 9 of phenylpyridines with electron-
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b512081k - View Online PAPER www.rsc.org/materials |...

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