Lighting Up Hypochlorous Acid through C(sp2)-H Hydroxylation with a Solvatochromic Organoiridium(III) Complex-based Probe

Abstract

Herein, we report the highly selective detection of the reactive oxygen species hypochlorous acid (HOCl) using a solvatochromic cyclometalated Ir(III) complex through a unique C(sp2)-H hydroxylation mechanism. The complex, Ir-1, exhibits pronounced solvatochromic behavior, showing a bathochromic luminescence shift from green to orange-red with increasing solvent polarity. Ir-1, constructed from a benzothiazole-substituted pyridyl-1,2,3-triazole ligand (L1), was synthesized and comprehensively characterized for the selective recognition of HOCl over other competing ROS, RNS, and anions. Detailed ESI-HRMS and 1H NMR titration studies reveal an unusual regio-and stereoselective syn-addition of HOCl across the triazole C=C bond, followed by β-elimination of HCl, resulting in selective C-H hydroxylation and enabling HOCl specific sensing. Theoretical calculations and electrochemical analyses indicate that triazole hydroxylation enhances the σ and π-donor strength of the L1 ligand in Ir-1-OH, modulating the energy gap between the 3LLCT and 3MLCT excited states and thereby inducing luminescence color switching. Furthermore, bioimaging studies in HEK-293T cells demonstrate that Ir-1 is capable of staining HOCl in the cell cytoplasm and nucleus, highlighting its potential for biological sensing applications.