Leveraging Metal Complexes for Microsecond Lifetime-Based Chloride Sensing

Chloride is the most abundant anion in cells and plays many critical roles in maintaining cellular homeostasis. However, current chloride indicators are rare with inherent sensitivity in their emission properties, such as vulnerability to pH changes or short emission lifetimes. These limitations restrict their application in aqueous media and imaging. In this work, we employed a transition-metal complex bearing pyridinium as a recognition unit for chloride and studied the phosphorescence emission properties. Iridium(III) complex 1 was synthesized as an alternative chloride-sensitive luminophore. The conjugable design also allows customization for the desired applications. Complex 1 exhibited high sensitivity and selectivity in chloride sensing across different physiological environments, regardless of pH fluctuation and ionic strength. Additionally, complex 1 featured a microsecond emission lifetime. The chloride sensing ability of complex 1 can be measured through both the luminescence intensity and long-lived phosphorescent lifetime, providing an alternative potential route for chloride imaging. The analogue 1b was successfully applied in the imaging of Cl^- in cellular environments and showed dose-dependent responses in both live and fixed cells.