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

- A series of cationic iridium complexes were synthesized and fully characterized.
- Photophysical and electrochemical properties of the complexes were investigated.
- DFT and TDDFT calculations were performed on complexes 1-4.
- The emission color of complexes can be tuned from yellowish-orange to blue.

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.

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