A "switch-on" photoluminescent and electrochemiluminescent multisignal probe for hypochlorite via a cyclometalated iridium complex

Abstract

A new cyclometalated iridium complex, [(bt)₂Ir(bpy-Fc)]PF₆ (bt = 2-phenylbenzothiazole, bpy-Fc = 4-ferrocenecarbonyl hydrazinocarbonyl-4'-methyl- 2,2'-bipyridine) (probe 1) was designed and synthesized for rapid photoluminescent (PL) and electrochemiluminescent (ECL) sensing of hypochlorite (ClO^-). Probe 1 exhibits weak PL and ECL emissions attributed to its electron transfer process. In the presence of ClO^-, the cleavage of the hydrazine-linked Fc moiety in probe 1 led to the enhancement of both PL and ECL. The photophysical and ECL properties of probe 1 were investigated and the proposed mechanism of the luminescence enhancement was confirmed by ¹H nuclear magnetic resonance spectroscopy, and PL and ECL investigations. In addition, the role of the Fc group in probe 1 in intra- and intermolecular electron transfer processes in the absence and presence of ClO^- is demonstrated for both PL and ECL processes. Further, a "switch-on" multi-signal method was developed for sensitive and selective detection of ClO^- with detection limits of 466 nM and 302 nM via PL and ECL techniques, respectively. Further, probe 1 was successfully applied for PL imaging of ClO^- in living macrophage cells. This work demonstrates that cyclometalated iridium complex bearing recognition and quenching groups is a promising "switch-on" probe in aqueous solutions to image living cells with high sensitivity and selectivity for biomedical applications.

Keywords: Electrochemiluminescence; Hypochlorite; Imaging; Iridium complex; Photoluminescence.