8-Quinolinolates as Ligands for Luminescent Cyclometalated Iridium Complexes Stefan Kappaun, † Stefan Sax, ‡ Sabrina Eder, ‡ Kai C. Mo ¨ller, § Kerstin Waich, | Fabian Niedermair, † Robert Saf, † Kurt Mereiter, ⊥ Josemon Jacob, # Klaus Mu ¨llen, # Emil J. W. List, ‡ and Christian Slugovc* ,† Institute of Chemistry and Technology of Organic Materials (ICTOS), Institute of Chemical Technology of Inorganic Materials (ICTAS), and Institute of Analytical Chemistry and Radiochemistry, Graz UniVersity of Technology, Stremayrgasse 16, A-8010 Graz, Austria, Institute of Solid State Physics, Graz UniVersity of Technology, Petersgasse 16, A-8010 Graz, Austria, Institute of Chemical Technologies and Analytics, Vienna UniVersity of Technology, Getreidemarkt 9/164SC, A-1060 Vienna, Austria, and Max-Planck-Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany ReceiVed NoVember 9, 2006 ReVised Manuscript ReceiVed February 7, 2007 Cyclometalated iridium(III) complexes have attracted considerable attention because of possible applications in oxygen sensing purposes 1 and, in particular, organic light- emitting devices (OLEDs). 2 Since the pioneering work of Forrest et al., 2 enormous experimental and theoretical efforts have focused on the design, synthesis, and characterization of different classes of homoleptic and heteroleptic iridium(III) complexes resulting in improved materials and device structures and, therefore, in increased efficiencies and enhanced brightness, as well as extended operational lifetimes of OLEDs fabricated from the corresponding phosphorescent compounds. 3 Concerning practical applications such as flat panel displays, tuning of the emission color to cover the entire visible spectrum is very desirable. Although a powerful color tuning from blue to red has been realized by modifications of the cyclometalating ligand, this approach suffers from the draw back of difficulties in the preparation of several μ-chloro bridged precursor materials and sometimes harsh conditions required for the formation of tris-cyclometalated iridium(III) complexes. 3 An alternative approach is based on heteroleptic iridium(III) complexes incorporating ancillary ligands such as acetylacetonate, picolinate, triazolate, and tetrazolate derivatives. 3a In most cases emission properties are still dominated by the nature of the cyclometalating ligands, but preparation of the corresponding heteroleptic compounds is noticeably facilitated compared to the synthesis of tris-cyclometalated complexes. 3,4 While there are numerous reports on luminescent metal complexes containing different derivatives of 8-hydroxy- quinoline (e.g., complexes of Al, B, Pd, etc.), 5 to our best knowledge investigations on iridium(III) complexes contain- ing quinolinolates are still rare. 6 Because of the possibility of tuning the energy gap by the attachment of electron- withdrawing or electron-donating groups, ligand centered excited states, and the commercial availability of many 8-hydroxyquinoline derivatives, 5 this class of ligands seems to be a promising candidate for the preparation of corre- sponding organoiridium(III) complexes. In this communication we wish to report the synthesis, structure, and thermal and photophysical as well as electro- luminescent properties of an up to date barely described class of iridium(III) complexes, namely, derivatives of bis- (κ 2 (C 2 ,N)-2-phenylpyridine)(κ 2 (N,O)-8-quinolinolate)irid- ium(III). We demonstrate that these easily prepared com- pounds exhibit emission characteristics controlled by the quinolinolate ligand and present a powerful tool for tuning materials properties affecting the absorption and emission characteristics as well as the thermal stability and OLED performance by simple modifications of the quinolinolate ligand. Therefore, the herein introduced results line up with recent reports on synthetically tailored iridium(III) com- pounds 7 and offer a versatile, cheap, and convenient approach for the fine tuning of iridium(III) complexes. All compounds under investigation were prepared from the μ-chloro bridged precursor material di-μ-chloro-tetrakis- † Institute of Chemistry and Technology of Organic Materials, Graz University of Technology. ‡ Institute of Solid State Physics, Graz University of Technology. § Institute of Chemical Technology of Inorganic Materials, Graz University of Technology. | Institute of Analytical Chemistry and Radiochemistry, Graz University of Technology. ⊥ Vienna University of Technology. # Max-Planck-Institute for Polymer Research. (1) DeRosa, M. C.; Hodgson, D. J.; Enright, G. D.; Dawson, B.; Evans, C. E. B.; Crutchley, R. J. J. Am. Chem. Soc. 2004, 126, 7619. (2) For examples see: (a) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.; Bredas, J. L.; Logdlund, M.; Salaneck, W. R. Nature 1999, 397, 121. (b) Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nature 2000, 403, 750. (3) For examples see: (a) You, Y.; Park, S. Y. J. Am. Chem. Soc. 2005, 127, 12438. (b) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho, N. N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg. Chem. 2005, 44, 1713. (c) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304. (d) Lamansky, S. Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Kwong, R.; Tsyba, I.; Bortz, M.; Mui, B.; Bau, R.; Thompson, M. E. Inorg. Chem. 2001, 40, 1704. (e) Holder, E.; Langeveld, B. M. W.; Schubert, U. S. AdV. Mater. 2005, 17, 1109. (f) Ragni, R.; Plummer, E. A.; Brunner, K.; Hofstraat, J. W.; Babudri, F.; Farinola, G. M.; Naso, F.; De Cola, L. J. Mater. Chem. 2006, 16, 1161. (4) (a) Kwon, T.-H.; Cho, H. S.; Kim, M. K.; Kim, J.-W.; Kim, J.-J.; Lee, K. H.; Park, S. J.; Shin, I.-S.; Kim, H.; Shin, D. M.; Chung, Y. K.; Hong, J.-I. Organometallics 2005, 24, 1578. (b) Zhao, Q.; Liu, S.; Shi, M.; Wang, C.; Yu, M.; Li, L.; Li, F.; Yi, T.; Huang, C. Inorg. Chem. 2006, 45, 6152. (5) For examples see: (a) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913. (b) Chen, C. H.; Shi, J. Coord. Chem. ReV. 1998, 171, 161. (c) Montes, V. A.; Li, G.; Pohl, R.; Shinar, J.; Anzenbacher, P., Jr. AdV. Mater. 2004, 16, 2001. (d) Kappaun, S.; Rentenberger, S.; Pogantsch, A.; Zojer, E.; Mereiter, K.; Trimmel, G.; Saf, R.; Mo ¨ller, K. C.; Stelzer, F.; Slugovc, C. Chem. Mater. 2006, 18, 3539. (e) Ghedini, M.; Aiello, I.; La Deda, M.; Grisolia, A. Chem. Commun. 2003, 2198. (f) Shavaleev, N. M.; Adams, H.; Best, J.; Edge, R.; Navaratnam, S.; Weinstein, J. A. Inorg. Chem. 2006, 45, 9410. (6) (a) Tsuboyama, A.; Mizutani, H.; Okada, S.; Takiguchi, T.; Miura, S.; Noguchi, K.; Moriyama, T.; Igawa, S.; Kamatani, J.; Furugori, M. Eur. Pat. Appl. 1211257 A2, 2002. (b) Ballardini, R.; Varani, G.; Indelli, M. T.; Scandola, F. Inorg. Chem. 1986, 25, 3858. (c) Kappaun, S.; Eder, S.; Sax, S.; Saf, R.; Mereiter, K.; List, E. J. W.; Slugovc, C. J. Mater. Chem. 2006, 16, 4389. (7) Lowry, M. S.; Bernhard, S. Chem.sEur. J. 2006, 12, 7970. 1209 Chem. Mater. 2007, 19, 1209-1211 10.1021/cm062666j CCC: $37.00 © 2007 American Chemical Society Published on Web 02/22/2007