10698 Chem. Commun., 2011, 47, 10698–10700 This journal is c The Royal Society of Chemistry 2011 Cite this: Chem. Commun., 2011, 47, 10698–10700 Iridium(III) soft salts from dinuclear cationic and mononuclear anionic complexes for OLED devicesw Gihane Nasr, a Audrey Guerlin, ab Fre´de´ric Dumur, c Layla Beouch, d Eddy Dumas, a Gilles Clavier, b Fabien Miomandre, b Fabrice Goubard, d Didier Gigmes, c Denis Bertin, c Guillaume Wantz e and Ce´dric R. Mayer* a Received 22nd June 2011, Accepted 19th August 2011 DOI: 10.1039/c1cc13733f Two iridium(III) soft salts based on ion-paired dinuclear cationic and mononuclear anionic complexes were designed and investigated as phosphorescent emitters for solution processed OLEDs. New dinuclear cationic complexes were prepared with two different bridging ligands, a carbazole and a phenylene spacer. Best devices were designed with the soft salt bearing a carbazole moiety. Organic Light-Emitting Diodes (OLEDs) using phosphorescent metal complexes have witnessed intense research efforts due to their potential applications in lighting and flat panel displays. 1 OLED displays are now available on the mass market but there is still pressure from industries for cutting costs and improving efficiencies. In this aim, incorporation of transition- metal complexes and especially of iridium(III) complexes in devices enables to overcome the limited quantum efficiencies of the conventional fluorescent OLEDs. 2 By the strong spin orbital coupling of the metal, both singlet and triplet excitons are harvested for light emission. 3 Neutral and ionic iridium(III) complexes can be both used as emitters in light-emitting devices as the two complexes display similar emissive properties. Neutral iridium(III) complexes have been without contest the most widely studied. 4 Despite their attractive emissive features, most of the robust neutral iridium(III) complexes can only be prepared in moderate yields under drastic conditions, notably for phenylpyridine-based complexes, and numerous complexes exhibit only a limited solubility in common solvents. In contrast, ionic complexes offer several advantages over neutral complexes. Ionic iridium(III) complexes are easier to prepare, synthesized in high yields under mild conditions, soluble in most polar solvents and even in aqueous media. To date, charged complexes were mostly used in Light-Emitting Electro- chemical Cells (LECs) where metal complexes act both as charge carriers and as light emitters. 5 Recently, soft salts formed by a pair of mononuclear cationic and anionic iridium(III) complexes proved to behave as neutral complexes in devices as no delay was detected between turn-on time and light emission, therefore demonstrating all the potential of this new approach based on charged complexes. 6 Easy color tunability could also be achieved by acting on the emission wavelength of both the anion and the cation and emission efficiencies comparable to those obtained with conventional neutral complexes-based OLEDs were also measured. Among ionic complexes, dinuclear iridium complexes were only scarcely investigated as emitters in light-emitting devices considering that only one report is available for OLEDs 7 and one for LECs. 8 However, their use in light-emitting devices has several advantages such as the introduction of two phosphorescent centers in one complex while controlling the intramolecular separation of the two metal centers which is a crucial parameter to improve the device performances. 9 The main part of the dinuclear complex is the bridging fragment, as it determines the nature of the interaction between both metal centers and, thereby, the electronic communication within the metallic dimer. Inter- actions are strongly dependent on the size, the shape, the rigidity, the planarity of the bridge. 10 To the best of our knowledge, no soft salts from mixed dinuclear cationic and mononuclear anionic complexes were investigated as emitters in OLED devices. The dinuclear iridium complexes CD 1 and CD 2 reported herein also constitute only the second examples of iridium dimers investigated in light-emitting devices containing a fully rigid and conjugated spacer. 7 For this first study, two different bridges were chosen, i.e. a phenylene group and a carbazole group. Both spacers were, respectively, obtained by condensation of 2,5-bis(hexyloxy)- benzene-1,4-dialdehyde and 9-(2-ethylhexyl) carbazole-3,6-di- carboxaldehyde with 1,10-phenanthroline-5,6-dione in acetic acid in the presence of ammonium acetate. The resulting imidazole derivatives were then reacted with Ir 2 (dfppy) 4 m-Cl 2 (dfppy = 2-(2,4-difluorophenyl)pyridine), affording the cationic dinuclear complexes CD 1 Á2PF 6 and CD 2 Á2PF 6 in 94% and a Institut Lavoisier de Versailles, UMR 8180 CNRS, Universite ´ de Versailles Saint Quentin en Yvelines, 45 av. des Etats-Unis, 78035 Versailles, France. E-mail: cmayer@chimie.uvsq.fr b Laboratoire PPSM, ENS Cachan, UMR 8531 CNRS, 61 avenue du Pre´sident Wilson, 94235 Cachan, France c Laboratoire Chimie Provence, e ´quipe CROPS, UMR 6264 CNRS, case 542, Universite ´s d’Aix-Marseille I, II, III, avenue Escadrille Normandie-Niemen, 13397 Marseille, France d Laboratoire LPPI, EA 2528, Universite ´ de Cergy-Pontoise, 5 mail Gay Lussac, Neuville-sur-Orge, 95031 Cergy-Pontoise Cedex, France e Laboratoire IMS, UMR 5218 CNRS, Ecole Nationale Supe ´rieure de Chimie et de Physique de Bordeaux, Universite´ de Bordeaux I, 16 avenue Pey Berland, 33607 Pessac Cedex, France w Electronic supplementary information (ESI) available: Synthetic procedures and spectroscopic data. See DOI: 10.1039/c1cc13733f ChemComm Dynamic Article Links www.rsc.org/chemcomm COMMUNICATION