Photophysical, electrochemical, and quantum chemical properties of cationic iridium complexes with tunable emission color

Abstract

We report the synthesis and characterization of the cationic iridium complexes [Ir(ppy)2(mpoxd)]PF6 (1), [Ir(dfppy)2(mpoxd)]PF6 (2), [Ir(piq)2(mpoxd)]PF6 (3), and [Ir(pq)2(mpoxd)]PF6 (4) bearing 2-phenylpyridine (Hppy), 2-(2,4-difluorophenyl)pyridine (Hdfppy), 1-phenylisoquinoline (Hpiq), and 2-phenylquinoline (Hpq) as cyclometalating ligands and 5-methyl-3-(2-pyridyl)-1,2,4-oxadiazole (mpoxd) as an ancillary ligand. UV–visible absorption spectra, photoluminescence (PL) emission spectra, and cyclic voltammetric measurements were obtained to explore the photophysical and electrochemical properties of 1–4. Depending on the nature of the cyclometalating ligands, the complexes emit yellow-orange to blue light in acetonitrile solution at room temperature. The significant blue shift in the emission spectrum of 2 is due to the presence of electron-withdrawing fluorine atoms on Hdfppy, which stabilizes the highest occupied molecular orbital (HOMO) to a greater extent than in the other complexes. The electrochemical and photophysical properties of the complexes were also calculated using density functional theory (DFT) and time-dependent DFT simulations. The results indicate that the optical properties of the complexes can be effectively tuned by selective design of the cyclometalating and ancillary ligands.