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A neutral phosphorescent coordination compound bearing benzimidazole ligand,Ir(pbi)2(acac) (Hpbi =1,2-diphenyl-lH-benzo[d]imidazole;Hacac =acetylacetone),is demonstrated to be the first example of sulfur-free iridium complex for detection of Hg2+ cation with high selectivity and sensitivity.Ir(pbi)2(acac) shows multisignaling response toward mercury(Ⅱ) ion through UV-vis absorption,phosphorescence and electrochemistry measurments.Upon addition of Hg2+ ion,the absorbance of MLCT transition band at 400 ～ 500 nm is weakened gradually;simultaneously,the absorption intensity of the π-ππ* transition band at 310 ～ 380 nm increases progressively (vide Figure 1);while its phosphorescence turns from bright green (λPLmax =520 nm) into faint skyblue (λPLmax =476 unm) (vide Figure 2).1H NMR spectroscopic titration as well as ESI-MS results indicate that the decomposition of Ir(pbi)2(acac) in the presence of Hg2+.