Pd-Catalyzed Functionalization of the Thenoyltrifluoroacetone Coligands by Aromatic Dyes in Bis(cyclometallated) Ir^III Complexes: From Phosphorescence to Fluorescence?

The synthesis, characterization and photophysical properties of a series of neutral Ir(CN-Meppy)₂(OO-tta-Ar) (MeppyH = 4-methyl-2-phenylpyridine; tta = thenoyltrifluoroacetonate) complexes containing new functionalized tta-Ar ligands in which the incorporated Ar group is an aromatic dye such as naphthalene, pyrene, naphthalimide or coumarin, are reported. The arylated proligands ttaH-Ar are readily obtained in two steps through Pd-catalyzed C-H bond activation of 2-acetylthiophene. In contrast to the parent Ir(CN)₂(OO) complexes, which are phosphorescent in solution at room temperature, all of the arylated complexes display fluorescence, and the phosphorescence emission is quenched. Thus, this work shows that the incorporation of such aromatic dyes in the tta ligand has a dramatic influence on the photophysical properties of the resulting Ir complexes.