A new 1,8-naphthalimide-based colorimetric and “turn-on” fluorescent Hg2+ sensor

A new fluorescent molecule 4-(bis(2-(ethylthio)ethyl)amino)-N-n-butyl-1,8-naphthalimide (BTABN) was reported. Its UV–vis absorption and fluorescence spectra were almost not dependent on the pH, but remarkably and selectively affected by Hg2+. Upon the addition of Hg2+ in EtOH/H2O (1/2, v/v), the absorption wavelength maxima were blueshifted from 436 nm to 376 nm with a naked-eye observed color change, and the fluorescence was greatly enhanced with a 14 nm blueshift within 1 min. Na+, K+, Ca2+, Mg2+, Cu2+, Zn2+, Cr3+, Pb2+, Ni2+, Fe2+, Mn2+, Co2+, Cd2+ showed no obvious interferences with the detection. The binding stoichiometry indicates that a 1:1 complex is formed between Hg2+ and BTABN. The response of the UV–vis absorption and the fluorescence spectra to Hg2+ can be attributed to the joint contribution of the PET and ICT process.

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► A new molecule for optically sensing Hg2+ in aqueous solutions is reported.
► Its UV–vis absorption and fluorescence spectra were carefully studied.
► The spectra are almost insensitive to H+ within a wide range of pH.
► The spectra are highly selective and sensitive to Hg2+.
► The spectra changes are the coefficient results of PET and ICT.