Zn2+-Induced aggregation of a water-soluble iridium complex enhances aggregation-induced emission for intracellular Zn2+ imaging

Abstract

Iridium(III) complexes show wide applications in biosensing and bioimaging, while Ir(III)-based Zn2+ probes are still rare and suffer from poor selectivity and low water solubility. In this work, we verified the phosphonate group as an efficient Zn2+ recognition moiety and developed a phosphonate-containing Ir(III) complex (Ir-BPA) as a water-soluble phosphorescent Zn2+ probe. Ir-BPA exhibited aggregation-induced emission enhancement (AIEE). Zn2+-binding also induced Ir-BPA aggregation, leading to enhanced phosphorescence and emission color changing from red to yellow. The binding mechanism was studied via spectra analysis, transmission electron microscope (TEM) images, and theoretical simulation. Ir-BPA was further employed in imaging intracellular Zn2+ level fluctuations via supplementary supply of Zn2+ source or endogenous release under oxidative stress. This work positively utilized AIEE properties of Ir(III) complexes in Zn2+ detection and broadened the strategies for developing water-soluble, AIE-active Ir(III) complexes for biological applications.