Two phosphorescent iridium(III) complexes containing simple l-alanine ligands as efficient sensors for Cu2+ ions

Two neutral iridium complexes Ir1 and Ir2 were synthesized using 2-(4-(trifluoromethyl)phenyl)pyridine (tfmppy) and 1-(4-(trifluoromethyl)phenyl)isoquinoline (tfmpiq) as cyclometalated ligands and l-alanine as ancillary ligand. The emission peaks of Ir1 and Ir2 are located at 518 nm and 610 nm and they exhibit intense green and red luminescence in acetonitrile solution with quantum efficiencies of 0.51 and 0.20. The effect of the modification of cyclometalated ligands on the spectral properties of the complexes was discussed in detail by theoretical calculation. After the addition of Cu2+ ions, the luminescence intensities of Ir1 and Ir2 were quenched by 90 % and 89 % respectively due to the paramagnetic effect formed by the combination of iridium complexes and Cu2+ ions. According to the titration experiment, a good linear relationship was found between the intensity at the emission peak and Cu2+ ions concentrations in the range of 0 μM to 15 μM, and the calculated detection limits were 0.54 μM and 0.59 μM. Moreover, the recognition of Cu2+ ions by Ir1 and Ir2 exhibits high interference and good reversibility. Therefore, complexes Ir1 and Ir2 containing simple amino acid as ancillary ligands can be used as “turn-off” phosphorescence sensors toward Cu2+ ions.