A simple fluorescent chemosensor 1 for the sequential detection of Hg2+ and cysteine or glutathione was developed by combination of thiosemicarbazide and 8-hydroxyjulolidine-9-carboxaldehyde. Sensor 1 exhibited an 'ON-OFF' fluorescence quenching response in the presence of Hg2+, which was explained by theoretical calculations. 1 also showed high selectivity in the presence of potential competitors such as Ag+ and Pb2+. Moreover, the resulting Hg2+-2.1 complex acted as an efficient 'OFF-ON' sensor for cysteine or glutathione, showing recovery of 2.1 from Hg2+-2.1 complex. Therefore, sensor 1 can be employed as a practical fluorescent chemosensor for recognition of Hg2+ and thiol-containing amino acids in aqueous solution.
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