A Dual-Target Fluorescent Probe with Response-Time Dependent Selectivity for Cd2+ and Cu2.

A novel fluorescent probe (NT) was developed by merging 2-hydrazinylbenzothiazole with 2-hydroxy-1-naphthaldehyde for the detection of Cd2+ and Cu2+. The probe alone is almost nonfluorescent due to the isomerization of C=N in the excited state. The addition of Cd2+ can cause an immediate strong green fluorescence owing to the suppression of C=N isomerization by Cd2+-coordination. Furthermore, NT gives a delayed turn-on fluorescence response to Cu2+ although it is a vigorous fluorescence quencher, which was thanks to the inhibition of the electron transfer between excited fluorophore and paramagnetic Cu2+ by sulfur donor. Based on fluorescence spectra and ESI-MS analysis, the binding modes between NT and Cd2+/Cu2+ were proposed.