Synthesis, characterization and in vitro antitumor activities of a biimidazole-chelated Ir(III) complex

In this paper, a new cyclometalated iridium(III) complex [Ir(ppy)2(mbiim)]Cl (Ir3) (in which mbiim = 1-Methyl-2,2'-biimidazole, ppy = 2-phenylpyridine) has been successfully synthesized and characterized by ESI-MS, UV-Vis spectroscopy and 1H NMR. The fluorescence properties of Ir3 have been studied in different pH value conditions. The fluorescence properties show that the fluorescence intensity of Ir3 decreases with the increase of pH in the experiment range, which is due to the protonation/deprotonation of active hydrogen of the imidazole ring on the imidazole ligand. Moreover, the photodynamic antitumor activities in vitro of three Ir(III) complexes have been investigated by MTT assay against four cell lines (HeLa, A549, A549R and LO2). These complexes exhibit low dark toxicity and high phototoxicity in three tumor cells. To our excitement, Ir3 has achieved satisfactory photodynamic therapy effects on cisplatin-resistant tumor cell lines A549R, while its toxicity towards normal cells is relatively lower. The results indicate that Ir3 is a relatively ideal photosensitizer, which may be developed into a new potential photodynamic therapy reagent against tumor.