Nitroolefin-modified cyclometalated iridium(III) complexes for tunable detection of biothiols with deep-red emission

Two cyclometalated iridium(III) complexes have been synthesized and utilized as turn-on luminescent probes for the detection of biothiols. These probes exhibited rapid (1 min) luminescence response toward biothiols. It was revealed that emission of probes increased significantly due to the Michael addition between biothiols and the double bond of nitroolefin in the iridium(III) complexes. The process was highly sensitive and the limits of detection for biothiols such as Hcy were evaluated to be 47.6 nM and 232 nM, respectively. The cyclometalated iridium(III) complex bearing electron-withdrawing ester groups showed deep-red emission at 643 nm in the presence of biothiols. It was further successfully applied in cell imaging.