A neutral phosphorescent coordination compound bearing a benzimidazole ligand, Ir(pbi)2(acac) (Hpbi = 1,2-diphenyl-1H-benzo[d]imidazole; Hacac = acetylacetone), is demonstrated to be the first example of a sulfur-free iridium complex for the detection of Hg2+ cations with high selectivity and sensitivity. Ir(pbi)2(acac) shows a multisignaling response towards mercury(II) ions through UV-vis absorption, phosphorescence and electrochemistry measurements. Upon addition of Hg2+ ions, solutions of this complex change from yellow to colorless, which could be observed easily by the naked eye, while its phosphorescence turns from bright green (λPLmax = 520 nm) into faint skyblue (λPLmax = 476 nm), and the detection limit is calculated to be 2.4 × 10−7 mol L−1. 1H NMR spectroscopic titration as well as ESI-MS results indicate that the decomposition of Ir(pbi)2(acac) in the presence of Hg2+ through rupture of Ir–O bonds is responsible for the significant variations in both optical and electrochemical signals.
