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

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.