Luminescent “Chugaev-type” cyclometalated iridium(III) complexes synthesized by nucleophilic addition of hydrazine

Abstract

In this work, we describe a series of six neutral Chugaev-type chelating dicarbene iridium complexes with different cyclometalating ligands. The effects of different cyclometalating ligands on the emission properties of dicarbene iridium complexes are evaluated. The triazole- and NHC-derived cyclometalating ligands combine with the strong σ–donating Chugaev-type dicarbene ligand, resulting in phosphorescence that is blue-shifted compared to previously described analogues. The complexes are synthesized by the nucleophilic addition of hydrazine to cationic bis-isocyanide iridium complexes, characterized by 1H, 13C{1H}, and 19F NMR spectroscopy as well as high-resolution mass spectrometry. Four of the six molecular structures of the dicarbene complexes were determined by X-ray crystallography. Electrochemical properties of the compounds were evaluated by cyclic voltammetry analysis, which provides evidence that the HOMO and LUMO energies are dependent on the cyclometalating ligands employed. All the Chugaev-type iridium complexes exhibit blue to blue-green phosphorescence in solution at 77 K and all but one in poly(methyl methacrylate) (PMMA) thin films at room temperature. Although the quantum yields for all the complexes are modest, we succeeded in blue-shifting the emission wavelength of these dicarbene-type iridium complexes.