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+.
Keywords: Ir(III) complexes; L-alanine; fluorine-substituted cyclometalated ligands; sensing copper ions.