Luminescent iridium(iii) complexes of N-heterocyclic carbene ligands prepared using the 'click reaction'

A series of imidazolium salt, N-heterocyclic carbene (NHC) ligand precursors, combined with 1,2,3-triazoles were synthesized using the Cu(i) catalyzed azide-alkyne cycloaddition 'click reaction'. These pro-ligands were prepared from imidazolium molecules that were functionalized with either a terminal alkyne or azide group. Methylation of the triazole unit with methyl iodide produced a series of imidazolium/triazolium NHC pro-ligands. From these pro-ligands a family of luminescent Ir(iii) complexes of the general form [Ir(ppy)2(C^N)]+ or [Ir(ppy)2(C^C)]+ (where ppy is 2-phenylpyridine and C^N represents a bidentate imidazolylidene/triazole ligand and C^C represents a bidentate imidazolylidene/triazolylidene ligand) were prepared. The electrochemical, photophysical and electrochemiluminescence properties of the complexes have been evaluated and a preliminary study of two of these compounds as luminescent probes for cell imaging studies was conducted in A549 human lung adenocarcinoma basal epithelial cells. Co-localisation studies with the commercial dye MitoTracker CMXRos were consistent with mitochondrial uptake for these compounds.