Synthesis, electrochemical and photochemical properties of neutral Ir(III) complex based on 3-Iodopyridine-2-carboxylate ligand

Abstract

In this work, we report the synthesis and characterization of mer-[Ir(ppy)2(Ipic)], where ppy = 2-phenylpyridine and Ipic = 3-iodopyridine-2-carboxylate, as well as, the electrochemical and photophysical properties in solution. The electronic absorption spectra profile can be divided into two main regions: intense bands in the high energy UV-region (200–300 nm) assigned to ligand centered (IL) transition on both the cyclometalated (ppy) and the ancillary (Ipic) ligands, and lower intensity absorption bands located in the less energetic region (320–460 nm) can be experimentally assigned to the spin-allowed metal-to-ligand charge transfer (1MLCT) transition and the spin-forbidden 3MLCT. From the electrochemical results, were obtained the oxidation peak (Ir(III)→Ir(IV) couple) at +0.59 V resulting in a HOMO of −5.09 eV, and the reduction potentials −1.65 and −2.00 V, which can be attributed to the Ipic and ppy, respectively. Additionally, it is possible to observe that the introduction of the halogen atom promotes a significant variation in LUMO energy (2.75 eV), while the HOMO level is almost unchanged. The complex displayed broad and structureless emission spectra in acetonitrile (λmax = 510 nm, φ = 0.0032 and τ = 160 ns) and dichloromethane (λmax = 510 nm, 525 nm) solution at room temperature but becomes structured (λmax = 490, 522 nm) in propionitrile:butyronitrile at 77 K, indicating that the emitting state at room temperature has a mixed 3MLCT-3LC character but at 77 K the emission has a strong 3LC character.