Fluorescence ‘on–off–on’ chemosensor for the sequential recognition of Hg2+ and cysteine in water

Abstract

A simple fluorescent chemosensor 1 for the sequential detection of Hg²⁺ and cysteine was developed by combination of benzene-1,2-diamine and 6-bromopyridine-2-carboxaldehyde. The sensor 1 exhibited an ‘on–off’ fluorescent quenching response in the presence of Hg²⁺, and could be applied for detection of Hg²⁺ with a good recovery in water samples. The sensing mechanism of 1 for Hg²⁺ was supported by theoretical calculations. Moreover, the resulting Hg²⁺–2·1 complex acted as an efficient ‘off–on’ sensor for cysteine, showing recovery of 1 from Hg²⁺–2·1 complex. Therefore, the sensor 1 can be employed as a practical fluorescent chemosensor for recognition of Hg²⁺ and cysteine in aqueous solution.