Ratiometric Phosphorescence Imaging of Hg(II) in Living Cells Based on a Neutral Iridium(III) Complex

In this work, a neutral iridium(III) complex [Ir(bt)2(acac)] (Hbt = 2-phenylbenzothiazole; Hacac = acetylacetone) has been realized as a Hg(II)-selective sensor through UV–vis absorption, phosphorescence emission, and electrochemical measurements and was further developed as a phosphorescent agent for monitoring intracellular Hg(II). Upon addition of Hg(II) to a solution of [Ir(bt)2(acac)], a noticeable spectral blue shift in both absorption and phosphorescent emission bands was measured. 1H NMR spectroscopic titration experiments indicated that coordination of Hg(II) to the complex induces fast decomposition of [Ir(bt)2(acac)] to form a new complex, which is responsible for the significant variations in optical and electrochemical signals. Importantly, cell imaging experiments have shown that [Ir(bt)2(acac)] is membrane permeable and can be used to monitor the changes in Hg(II) levels within cells in a ratiometric phosphorescence mode.