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

A pi-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 pi-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 mu M) and displayed comparatively higher cytotoxicity behaviour to cis-platin. image