Colorimetric and photoluminescent probes based on iridium(III) complexes for highly selective detection of homocysteine

As a biological thiol closely related to the incidence of gastric cancer, homocysteine (Hcy) has been reported to be detected in vivo and in vitro. The design of ratiometric photoluminescent probes often relies on the unique chemical structure of the molecular. In this paper, we designed and synthesized three aldehyde-containing iridium(III) complexes and characterized their structure and photophysical properties. They showed a good specificity for Hcy detection. The color of the solution gradually changed from red to pale yellow. The photoluminescent variation from red to green was observed by the naked eye after addition of Hcy to the solution of the Ir1 ([(CHO-pba)2Ir(bpy-2NH2)]PF6), Ir2 ([(CF3-pba)2Ir(bpy-2NH2)]PF6) and Ir3 ([(CH3-pba)2Ir(bpy-2NH2)]PF6) with a large blue shift by 120, 63 and 106 nm, respectively. Based on the differences in their structures, it could be inferred that this type of ratiometric photoluminescent probe based on iridium(III) complexes with aldehyde was related to the strong electron-donating effect of the nitrogen-containing substituents on the bipyridine ligand in the structure, and the introduction of electron-donating groups on the 4-(2-pyridinyl)benzaldehyde (pba) ligand can enlarge the blue shift of the photoluminescent wavelength upon sensing of Hcy. On the other hand, iridium(III) complexes are currently recognized as a third-generation good photodynamic therapy photosensitizer. The photodynamic therapy properties of the three iridium(III) complexes in this article have also been evaluated. All of them have strong singlet oxygen generation ability and low cytotoxicity which are expected to be used in photodynamic therapy and Hcy detection.