Monodentate Benzo[d]imidazole-Based Iridium(III) Complexes and Their Dual Fluorescent and Phosphorescent Emissions

초록

We herein reported the preparation of three heteroleptic iridium complexes possessing the monodentate benzo[d]imidazole ligand, namely IrBzH (bis[2-(4,6-difluorophenyl)pyridinato-C<^>N](1-pyridin-2-yl)-1H-benzo[d]imidazolate)iridium(III)), IrBzCN (bis[2-(4,6-difluorophenyl)pyridinato-C<^>N](2-(1H-benzo[d]imidazolate-1-yl)isonicotinonitrile)iridium(III)), and IrBzBr (bis[2-(4,6-difluorophenyl)pyridinato-C ' N](1-(4-bromopyridin-2-yl)-1H-benzo[d]imidazolate)iridium(III)). The successful preparation of these complexes was confirmed by multinuclear NMR spectroscopy and elemental analysis, while the molecular structures were determined by X-ray diffraction. The photoluminescence spectra of all three complexes in toluene at ambient temperature exhibited a dual-emissive pattern in the high- and low-energy regions. For IrBzCN and IrBzBr, the emissions were simultaneous in accordance with the excitation energies (lambda(em) = 342 and 370 nm), indicating that exhibiting both fluorescent (in the high-energy region) and phosphorescent (in the low-energy region) emissions is an inherent property of these complexes. Time-dependent density functional theory calculations verified that each fluorescent emission of the Ir complexes is associated with a ligand-to-ligand charge transfer transition, and the phosphorescent emission can be attributed to typical triplet metal-to-ligand charge transfer transitions between Ir3+ and the difluorophenylpyridine ligand.

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