Orange/red light emitting iridium(III) organometallic complexes containing 2,3-di(pyridine-2-yl)quinoxaline as ancillary ligand and their anticancer properties

A π-electron rich ligand, 2,3-di(pyridine-2-yl)quinoxaline, was introduced in Ir(III) coordination sphere along with four different cyclometallating ligands to obtain four new complexes (Ir1–Ir4) of formula [Ir(C N)₂(pyrquinox)]PF₆ {where C N is monoanionic cyclometallating ligand; 2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine (F₂CF₃ppy), 2,5-diphenylbenzoxazole (phox), 2,3-diphenylquinoxaline (phquinox) and pyrquinox=2,3-di(pyridine-2-yl)quinoxaline}. Structure of Ir1 was determined from single crystal X-ray structure analysis and found it to be a bis-heteroleptic Ir(III) mononuclear octahedral complex of formula [Ir(ppy)₂(pyrquinox)]PF₆. A very same structural formulation of Ir2–Ir4 was supported by different spectroscopic and analytical data. Theoretical calculations were helpful in understanding the optical and electrochemical properties of Ir1–Ir4. The effect of rich π-electrons ancillary ligand (pyrquinox) was observed on luminescence properties of the complexes, which on irradiation produced emissions in the orange and red spectral regions. The cytotoxic behaviours of Ir1–Ir4 were explored against MCF-7 cell line through MTT assays. The obtained IC₅₀ values were found in low micromolar region (5–8 μM) and displayed comparatively higher cytotoxicity behaviour to cis-platin.