A dual-channel sensor containing multiple nitrogen heterocycles for the selective detection of Cu2+, Hg2+ and Zn2+ in same solvent system by different mechanism

A molecule 3 containing multiple nitrogen heterocycles has been designed and synthesized. The systematical studies on sensing behaviors of compound 3 in DMSO/H2O by fluorescent and UV-vis absorption spectra indicate that this molecule shows the selectivity to Cu2+, Hg2+ and Zn2+ by dual-channels. Compound 3 shows significant fluorescence quenching to both Cu2+ and Hg2+ but with a red-shift for Hg2+, and only for Zn2+ there are fluorescence colorimetric and ratiometric changes. Furthermore, the absorption spectrum of 3 to Cu2+ also exhibits ratiometric change with the color change of solution from colorless to yellow, while no similar response to Hg2+ and Zn2+. These changes can be recognized via naked eyes. Three kinds of different mechanism have been convincingly proposed through ESI-Mass, H-1 NMR titration, FT-IR spectra and DFT calculation. The suitable pH range of sensor 3 to Cu2+, Hg2+, Zn2+ has been determined to be 5.1-13.3, 6.9-11.2, 5.1-12.2, respectively. And time response experiments show that, as a fast-responsive fluorescent sensor for three kinds of cations, it can be used for the real-time analysis of Hg2+. Particularly, the reversible detection of Cu2+ in 5 cycles indicates that sensor 3 is expected to be a molecular logic gate for Cu2+.