Iridium(III) coordination compounds based on organophosphorus ancillary ligands showing cytotoxicity against breast cancer cells and Fe(III) luminescent sensing.

Three phosphorescent iridium(III) complexes consisting bis-diphosphine ligands were prepared and characterized by single-crystal XRD, CHN analysis, spectroscopic techniques, cyclic voltammetry, and DFT. The synthesized complexes were the three monomeric [Ir(ppy)2(L1)Cl] (1), [Ir(ppy)2(L2)]Cl (2) and [Ir(ppy)2(L3)]Cl (3) where L1 = bis-(diphenylphosphino)methane (dppm), L2 = bis-(diphenylphosphino)propane (dppp) and L3 = bis-(diphenylphosphino)benzene (dppbe). Complexes 1-3 gave an absorption band between 240 to 380 nm in both CH2Cl2 and DMSO, which is assigned as a charge transfer transition based on theoretical calculation. They showed a blue-green emission at 460-520 nm in DMSO with an absolute quantum efficiency of 0.013-0.046 at room temperature. The selective photo-induced electron transfer (PET) by Fe3+ in DMSO, was studied to obey the Rehm-Weller principle. The 1:1 binding soichiometry between 1-3 and Fe3+ was established by Job's plot. The binding constants (Ka) were determined using the Benesi-Hildebrand plot. All the complexes are extremely more potent than cisplatin for in vitro antiproliferative activity towards the human breast cancer cells, HCC1937, MCF-7, and MDA-MB-231. The values of IC50 were in the range of 0.077-0.485 μM, and 1 exhibited the most effective IC50 against MDA-MB-231 cell line, the triple-negative breast cancer cell. Their lipophilicities (log P) were also examined to explain the penetration ability of the studied complexes towards cell barriers, and transport to the molecular target.