Coumarin Thiourea-Based Fluorescent Turn-on Hg2+ Probe That Can Be Utilized in a Broad pH Range 1-11.

A novel coumarin-thiourea conjugate was synthesized facilely. It served as a fluorescent turn-on chemosensor for selective detection of Hg2+ ion over other common competitive metal ions including Li+, Na+, K+, Ag+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+, Mn2+, Sr2+, Ca2+, Mg2+, Al3+, Cr3+ and Fe3+ ions based on the Hg2+-promoted desulfurization and cyclization reactions. Addition of Hg2+ ion to the sensor solution in 2:8 EtOH/H2O induced a hypsochromic shift of the UV-Vis absorption band from 360 nm to 340 nm accompanying distinct enhancement in the absorption intensity while addition of other metal ions failed to bring about substantial change in the absorption spectra. Addition of Hg2+ to the sensor solution also caused marked increase in the fluorescence emission intensity and most common competitive metal ions did not interfere with the selective sensing of Hg2+ ion by the sensor. The detection limit of Hg2+ ion by the probe was calculated to be 1.46 × 10-7 M and the probe could be utilized for selective detection of Hg2+ ion by fluorescence turn-on mode over a broad pH range of 1-11.