Fluorometric and colorimetric detection of hypochlorous acid and hypochlorite by a naphthalimide–dicyanoisophorone conjugate

A naphthalimide–dicyanoisophorone conjugate (1) was synthesized and used as a chemodosimeter for fluorometric and colorimetric detection of hypochlorous acid (HClO) and hypochlorite (OCl–) in aqueous media. This molecule shows a strong reddish-purple color and a weak fluorescence, but HClO/OCl–-selective oxidative decomposition of the dicyanoisophorone moiety promotes a color fading and a fluorescence enhancement. Ab initio calculation revealed that these responses to HClO/OCl– originate from the suppression of intramolecular electron transfer from the photoexcited naphthalimide moiety by the decomposition of the dicyanoisophorone moiety. These colorimetric and fluorometric responses facilitate relatively rapid (∼5 min), selective, and sensitive detection of HClO/OCl– as low as ∼1.3 μM under physiological conditions.