Luminescent Platinum(II) Complexes Containing Isoquinolinyl Indazolate Ligands: Synthetic Reaction Pathway and Photophysical Properties Sheng-Yuan Chang, Jakka Kavitha, Jui-Yi Hung, and Yun Chi* Department of Chemistry, National Tsing Hua UniVersity, Hsinchu 300, Taiwan Yi-Ming Cheng, Elise Y. Li, Pi-Tai Chou,* and Gene-Hsiang Lee Department of Chemistry and Instrumentation Center, National Taiwan UniVersity, Taipei 106, Taiwan Arthur J. Carty* Steacie Institute for Molecular Sciences, National Research Council, Ontario K1A 0R6, Canada Received May 7, 2007 New Pt(II) dichloride complexes [Pt(1-iqdzH)Cl 2 ](2a) and [Pt(3-iqdzH)Cl 2 ](2b), in which idqzH ) 1- or 3-isoquinolinyl indazole, were prepared by treatment of the corresponding indazoles with K 2 PtCl 4 in aqueous HCl solution. Despite their nonemissive nature, these complexes could react with excess indazole, sodium picolinate, and 3-trifluoromethyl- 5-(2-pyridyl) pyrazole [(fppz)H] to afford the respective a and b series of luminescent complexes [Pt(1-iqdz)(L ∧ X)] and [Pt(3-iqdz)(L ∧ X)], where L ∧ X ) 1-iqdz (1a), 3-iqdz (1b), pic (3a, 3b), and fppz (4a, 4b). Single-crystal X-ray diffraction studies of 1b, 2a, and 3b revealed a planar molecular geometry without notable intermolecular Pt‚‚‚Pt contact in the solid crystal, a result of the steric repulsion imposed by the bulky indazole fragments. For coordination complexes 1, 3, and 4, photoluminescence in degassed CH 2 Cl 2 revealed high quantum efficiency and short radiative lifetimes in the range of several microseconds. As supported by the spectral feature, the associated radiation lifetimes, and a computational approach based on time-dependent density function theory (TD-DFT), the origin of the emission is attributed to a mixed 3 MLCT/ 3 ππ transition. The TD-DFT approach further confirmed that, except for the series 1 complexes, the HOMO of 3-iqdz complexes 3b and 4b is much less located at the central Pt(II) atom than the HOMO orbitals of the respective 1-iqdz complexes 3a and 4a, leading to a smaller degree of MLCT contribution. Consequently, there are a blue-shifted emission signal and an inferior emission quantum yield for the 3-iqdz derivatives. OLED devices with a multilayer configuration of ITO/NPB/CBP:3a/BCP/Alq 3 /LiF/Al were fabricated using a CBP layer doped with various concentrations of 3a, ranging from 6% to 100%, within the emitting layer. The best device performance was realized using a 6% doping concentration, for which the external quantum yield of 4.93%, luminous efficiency of 12.19 cd/A, and power efficiency of 6.12 lm W -1 were observed at 20 mA/cm 2 , while a maximum luminescence as high as 20296 cd/m 2 was also realized at 16 V, showing good prospect for the fabrication of Pt(II) based OLEDs. The third-row transition metal complexes have been extensively utilized for the fabrication of various types of phosphorescent organic light emitting diodes (OLEDs). 1 The imposed strong spin-orbit coupling, which is made possible by introduction of a heavy transition metal element into the skeleton of the complexes, effectively breaks down the spin conservation rule, facilitating a change in multiplicity and * To whom correspondence should be addressed. E-mail: ychi@ mx.nthu.edu.tw (Y.C.); chop@ntu.edu.tw (P.-T.C.); carty.arthur@ic.gc.ca (A.J.C.). Fax: +886 3 572 0864 (Y.C.); +886 2 2369 5208 (P.-T.C); +1 613 953 7592 (A.J.C.). (1) (a) Holder, E.; Langeveld, B. M. W.; Schubert, U. S. AdV. Mater 2005, 17, 1109. (b) Yersin, H. Top. Curr. Chem. 2004, 241, 1. (c) Welter, S.; Brunner, K.; Hofstraat, J. W.; De Cola, L. Nature 2003, 421, 54. (d) Sun, Y.; Giebink, N. C.; Kanno, H.; Ma, B.; Thompson, M. E.; Forrest, S. R. Nature 2006, 440, 908. (e) Chou, P. T.; Chi, Y. Eur. J. Inorg. Chem. 2006, 3319. Inorg. Chem. 2007, 46, 7064-7074 7064 Inorganic Chemistry, Vol. 46, No. 17, 2007 10.1021/ic700877n CCC: $37.00 © 2007 American Chemical Society Published on Web 07/26/2007