Cyclometallated imidazo-phenanthroline iridium complexes and their anticancer activity

Abstract

Abstract Cyclometallated mononuclear iridium complexes (1–3) were synthesized using dimeric precursor [\((\hbox {ppy})_{2}\hbox {Ir}^{\mathrm{III}}(\upmu \hbox {-Cl})]_{2}\) and imidazo-phenanthroline-based ligands (\(\mathbf{L}_{1}\)–\(\mathbf{L}_{3})\). The complexes were characterised using various analytical techniques. The complexes exhibited spin forbidden metal-to-ligand charge transfer (MLCT) transitions at wavelengths \({>}300 \hbox { nm}\) and high energy ligand-based transition below 300 nm. The complexes were found to be emissive and displayed emission bands at 580 nm upon excitation at 380 nm with quantum yields 0.07 with respect to standard [\(\hbox {Ru}(\hbox {bpy})_{3}]\hbox {Cl}_{2}\). The complexes 1–3 showed dose-dependent suppression of cell viability (\(\hbox {IC}_{50}\) values \({\sim }2.5 \,\upmu \hbox {M}\)) towards human breast (MCF7) cancer cell line. The hydrophobicity measurements and flow cytometry analysis suggest that cellular uptake is primarily responsible for observed cytotoxicity.GRAPHICAL ABSTRACT Synopsis Mononuclear anticancer-active cyclometallated iridium complexes (1–3) using imidazo-phenanthroline-based ligands (\(\mathbf{L}_{1}\)–\(\mathbf{L}_{3})\) were synthesized.