Multicolor Emissive Phosphorescent Iridium(III) Complexes Containing L-Alanine Ligands: Photophysical and Electrochemical Properties, DFT Calculations, and Selective Recognition of Cu(II) Ions

Abstract

Three novel Ir(III) complexes, (ppy)2Ir(L-alanine) (Ir1) (ppy = 2-phenylpyridine), (F4ppy)2Ir(L-alanine) (Ir2) (F4ppy = 2-(4-fluorophenyl)pyridine), and (F2,4,5ppy)2Ir(L-alanine) (Ir3) (F2,4,5ppy = 2-(2,4,5-trifluorophenyl)pyridine), based on simple L-alanine as ancillary ligands were synthesized and investigated. Due to the introduction of fluorine substituents on the cyclometalated ligands, complexes Ir1–Ir3 exhibited yellow to sky-blue emissions (λem = 464–509 nm) in acetonitrile solution. The photoluminescence quantum yields (PLQYs) of Ir1–Ir3 ranged from 0.48–0.69, of which Ir3 with sky-blue luminescence had the highest PLQY of 0.69. The electrochemical study and density functional theory (DFT) calculations show that the highest occupied molecular orbital (HOMOs) energy of Ir1–Ir3 are stabilized by the introduction of fluorine substituents on the cyclometalated ligands, while L-alanine ancillary ligand has little contribution to HOMOs and lowest unoccupied molecular orbitals (LUMOs). Moreover, Ir1–Ir3 presented an excellent response to Cu2+ with a high selectivity, strong anti-interference ability, and short response time. Such a detection was based on significant phosphorescence quenching of their emissions, showing the potential application in chemosensors for Cu2+.