Cascade recognition of Hg2+ and cysteine using a naphthalene based ESIPT sensor and its application in a set/reset memorized device

Abstract

An optical ESIPT sensor for Hg²⁺ and cysteine based on a naphthalene platform (1) was designed and synthesized by a one step reaction and characterized by using common spectroscopic techniques. Upon addition of Hg²⁺ to a 9 : 1 (v/v) aqueous CH₃CN (pH 7.0 HEPES buffer) solution of 1, the highly fluorescent probe becomes weakly fluorescent, showing a color change from colorless to dark yellow visible to the naked eye and from fluorescent blue to light yellow when irradiated with 365 nm light. The sensing mechanism has been supported by DFT and ¹H NMR titration studies. The in situ generated 1–Hg²⁺ complex has been used for effectively sensing Cys. Owing to the stronger binding affinity of the sulfhydryl group to Hg²⁺, Cys can extract Hg²⁺ from the 1–Hg²⁺ complex, resulting in the release of 1 and revival of the emission intensity. Sensor 1 has also been successfully applied for the detection of Hg²⁺ in real water samples with good recovery. The alternate addition of Hg²⁺ and Cys ions generated “on–off–on” fluorescence cycles, which enabled 1 to be used as a reversible and reconfigurable set/reset memorized device at the molecular level.