Synthesis, Characterization, and DFT/TD-DFT Calculations of Highly Phosphorescent Blue Light-Emitting Anionic Iridium Complexes Davide Di Censo, † Simona Fantacci,* ,‡ Filippo De Angelis, ‡ Cedric Klein, † Nick Evans, † K. Kalyanasundaram, † Henk J. Bolink, § Michael Gra 1 tzel, † and Mohammad K. Nazeeruddin* ,† Laboratory for Photonics and Interfaces, Station 6, Institute of Chemical Sciences and Engineering, School of basic Sciences, Swiss Federal Institute of Technology, CH - 1015 Lausanne, Switzerland, Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR), c/o Dipartimento di Chimica, UniVersita ` di Perugia, I-06123, Perugia, Italy, and Institute of Molecular Science, UniVersity of Valencia, P.O. Box 22085 ES-46071 Valencia, Spain Received September 14, 2007 Highly phosphorescent blue-light-emitting anionic iridium complexes (C 4 H 9 ) 4 N[Ir(2-phenylpyridine) 2 (CN) 2 ](1), (C 4 H 9 ) 4 N- [Ir(2-phenyl-4-dimethylaminopyridine) 2 (CN) 2 ](2), (C 4 H 9 ) 4 N[Ir(2-(2,4-difluorophenyl)-pyridine) 2 (CN) 2 ](3), (C 4 H 9 ) 4 N[Ir- (2-(2,4-difluorophenyl)-4-dimethylaminopyridine) 2 (CN) 2 ](4), and (C 4 H 9 ) 4 N[Ir(2-(3,5-difluorophenyl)-4-dimethylaminopyridine) 2 - (CN) 2 ](5) were synthesized and characterized using NMR, UV-vis absorption, and emission spectroscopy and electrochemical methods. In these complexes color and quantum yield tuning aspects are demonstrated by modulating the ligands with substituting donor and acceptor groups on both the pyridine and phenyl moieties of 2-phenylpyridine. Complexes 1-5 display intense photoluminescence maxima in the blue region of the visible spectrum and exhibit very high phosphorescence quantum yields, in the range of 50-80%, with excited-state lifetimes of 1-4 μs in acetonitrile solution at 298 K. DFT and time dependent-DFT calculations were performed on the ground and excited states of the investigated complexes to provide insight into the structural, electronic, and optical properties of these systems. Introduction Iridium(III) cyclometalated complexes are attracting wide- spread interest because of their unique photophysical proper- ties and applications in organic light-emitting diodes (OLEDs). 1-4 The main requirements for OLEDs are that the phosphorescent emitter should have sharp colors in the blue, green, and red region and exhibit very high phosphorescence quantum yields. Even though there are several iridium complexes that exhibit green and red phosphorescence colors, blue-emitting iridium complexes, particularly in the deep blue region, are still scarce. Thus, the design and development of blue-light-emitting iridium complexes is a highly desirable and pursued task. 4-7 In principle, to blue-shift the emission in iridium(III) complexes can be realized by properly choosing substituents on the 2-phenylpyridine ligands or on the bipyridine (or phenanthroline) which stabilize the HOMO and/or destabilize the LUMO, thus increasing the HOMO- LUMO gap. 8,9 This strategy has been chosen by Slinker et al., who used fluorinated 2-phenylpyridine ligands to obtain iridium cationic complexes that show green-blue and green electroluminescence. 10 In these complexes the increase in the HOMO-LUMO gap with respect to complexes without * To whom correspondence should be addressed. E-mail: mdkhaja.nazeeruddin@epfl.ch (M.K.N.); simona@thch.unipg.it (S.F.). † Swiss Federal Institute of Technology. ‡ ISTM-CNR Perugia. § University of Valencia. (1) Adachi, C.; Baldo, M. A.; Forrest, S. R.; Thompson, M. E. Appl. Phys. Lett. 2000, 77. (2) Baldo, M. A.; Lamansky, S.; Burrows, P. E.; Thompson, M. E.; Forrest, S. R. Appl. Phys. Lett. 1999, 75, 4. (3) Ikai, M.; Tokito, S.; Sakamoto, Y.; Suzuki, T.; Taga, Y. Appl. Phys. Lett. 2001, 79, 156. (4) Nazeeruddin, M. K.; Humphry-Baker, R.; Berner, D.; Rivier, S.; Zuppiroli, L.; Gra ¨tzel, M. J. Am. Chem. Soc. 2003, 125, 8790-8797. (5) Coppo, P.; Plummer, E. A.; De Cola, L. Chem. Commun. 2004, 1774- 1775. (6) Lowry, M. S.; Hudson, W. R.; Pascal, R. A. J.; Bernhard, S. J. Am. Chem. Soc. 2004, 126, 14129. (7) Lowry, M. S.; Goldsmith, J. I.; Slinker, J. D.; Rohl, R.; Pascal, R. A.; Malliaras, G. G.; Bernhard, S. Chem. Mater. 2005, 17, 5712. (8) You, Y.; Park, S. Y. J. Am. Chem. Soc. 2005, 127, 12438-12439. (9) Sajoto, T.; Djurovich, P. I.; Tamayo, A.; Yousufuddin, M.; Bau, R.; Thompson, M. E.; Holmes, R. H.; Forrest, S. R. Inorg. Chem. 2005, 44, 7992-8003. (10) Slinker, J. D.; Gorodetsky, A. A.; Lowry, M. S.; Wang, J.; Parker, S.; Rohl, R.; Bernhard, S.; Malliaras, G. G. J. Am. Chem. Soc. 2004, 126, 2763. Inorg. Chem. 2008, 47, 980-989 980 Inorganic Chemistry, Vol. 47, No. 3, 2008 10.1021/ic701814h CCC: $40.75 © 2008 American Chemical Society Published on Web 01/03/2008