The reduction performance of double bonds regulated by the competition of push-pull electron groups to realize the colorimetric and fluorescence recognition of hypochlorous acid

Based on its reducibility, the double bond can act as a reaction site for hypochlorous acid (HOCl), which had been demonstrated by a great deal of work. Nevertheless, the reactivity is influenced by the adjacent chemical environment. Therefore, in this work, we constructed a probe (QI) by methoxy-substituted quinoline conjugating dicyanoisoflurone, in which dicyano and pyridine N act as electron-withdrawing groups and the methoxy acts as an electron-donating group, to regulate their adjacent C=C reactivity. The push-pull electron effect between the methoxy group and the pyridine N led to the C=C bond being passivated. On the other hand, another C=C bond was activated by the strong electron-pulling effect of the dicyano group. Thus, the previously weak intramolecular charge transfer became stronger after the dicyano adjacent to the C=C was oxidized by HOCl, and showed a strong emission shifted from 570 to 520 nm along with a color change. The reaction mechanism was verified by mass spectrometry, NMR and theoretical calculation, and further bioimaging demonstrated the practical application of the probe.