Phosphorescent Heteroleptic Iridium(III) Complexes with Cyclometalating 1,2,3-Triazol-5-ylidene Mesoionic Carbene Ligands

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Five neutral heteroleptic cyclometalated iridium(III) complexes with the chemical formula [Ir(C^N)2(C^C)] are described, where C^C is a cyclometalated 1-aryl-1H-1,2,3-triazol-5-ylidene mesoionic carbene (MIC, aryl = phenyl or 4-(trifluoromethyl)phenyl). The MIC with the unsubstituted phenyl substituent was paired with four different cyclometalating (C^N) ligands, namely 1-phenylisoquinoline, 2-phenylbenzothiazole, 2-phenylpyridine, and 2-(2,4-difluorophenyl)pyridine. The other combination is between the 4-(trifluoromethyl)phenyl MIC and the 2-(2,4-difluorophenyl)pyridine ligand. The five complexes are characterized by NMR (1H, 13C{1H}, and 19F), with crystal structures determined for three of them. Cyclic voltammetry was used to measure redox potentials, which vary as a function of the C^N ligand. Photophysical analysis of the compounds indicates that their photoluminescence profiles are strongly dependent on the C^N ligands that are paired with the MIC, minimally perturbed when the CF3 group is introduced to the MIC. PL quantum yields (ΦPL) up to 0.85 in poly(methyl methacrylate) films were obtained, with PL lifetimes spanning the range of 1.2–1.9 μs in the same medium.