Synthesis, characterization, and DFT investigation of IrIII tolylterpyridine complexes

Three new polypyridine iridium(III) complexes [(IrCl)-Cl-III(L)-(tterpy)](PF6)(2) (L = phen (1), dpphen (2), and dmbpy (3)) were prepared. Reference complexes [(IrCl)-Cl-III(bpy)(tterpy)](PF6)(2) (4) and [Ir-III(L)(2)](PF6)(3) (L = tterpy (5) and terpy (6)) were also prepared. Abbreviations of the ligands used here are phen = 1,10-phenanthroline, dpphen = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, tterpy = 4'-(4-tolyl)-2,2':6',2"-terpyridine, and terpy = 2,2':6',2"-terpyridine. The syntheses, which were accomplished in typical reaction times of fifteen minutes by using a microwave oven, were easier than a previous method. The complexes were characterized by electrospray mass spectrometry, UV/Vis spectroscopy, and cyclic voltammetry (CV). The X-ray structures of the two complexes 5 and 6 were also obtained. Cyclic voltammograms of all the [(IrCl)-Cl-III(L)(tterpy)](2+) complexes showed that the first reduction occurred at around -0.67 V, which is attributed to the reduction of the tterpy ligand in [(IrCl)-Cl-III(L)(tterpy)](2+). The electronic properties of complexes 5 and 6 were studied by using B3LYP functional calculations, and their optimized geometries were compared to those of the experimentally observed ones. Excited triplet and singlet states are also examined by using time-dependent density functional theory (TDDFT). The calculated energies of the lowest singlet and triplet states in the two complexes are in good agreement with the experimental absorption and phosphorescence spectra. In this study, it was found that [(IrCl)-Cl-III(L)(tterpy)](2+) emits an intense phosphorescence at room temperature. Since the lowest unoccupied molecular orbitals (LUMOs) of all [(IrCl)-Cl-III(L)-(tterpy)](2+) complexes are composed of the pi*-system contribution of the tterpy ligand, the spectroscopic and electrochemical results are discussed comparatively, ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).