Synthesis, structural characterization and biological properties of cyclometalated iridium(iii) complexes containing [1,2,5]-thiadiazolo-[3,4-f]-[1,10]-phenanthroline

Abstract

Two cationic iridium(III) complexes, [Ir(ppy)₂((tdzp))]⁺ (1) and [Ir(bhq)₂((tdzp))]⁺ (2) {ppy = 2-phenylpyridine, bhq = benzo[h]quinoline, tdzp = [1,2,5]-thiadiazolo-[3,4-f]-[1,10]-phenanthroline}, have been synthesized and structurally characterized. The molecular structures of the iridium complexes have been confirmed by single-crystal X-ray structure determination. Extensive hydrogen bonding between lattice water molecules, solvated methanol, and chloride anions is observed in the crystal structure of complex 1, which leads to the formation of 1D polymeric cyclic hybrid water–chloride–methanol clusters. The complexes show different photophysical properties in different solvents. The experimental photo-physical properties of the synthesized iridium(III) complexes match well with the theoretically calculated results obtained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies. The HOMO of complexes 1 and 2 is restricted on the iridium and cyclometalated aromatic ligands, while the LUMO, LUMO+1, and LUMO+2 are primarily restricted on the polypyridyl tdzp ligand. The interaction of the complexes with calf thymus DNA (CT-DNA) was investigated by absorption titration and emission titration experiments. Furthermore, the cytotoxicity and cellular localization properties of these complexes towards HeLa cells have been investigated.