Photometric sensing of heavy metal ions using a naphthoquinodimethyl-bis-thioamide dye: Selectivity & Photophysics of the metal organic complexes

As Mother Nature is experiencing catastrophic environmental pollutions from both natural sources and anthropogenic activities, many scientists have been working around the clock to develop environmentally benign and cost-effective, yet sensitive, detection techniques for pollutants, especially heavy metal species (e.g. lead, cadmium, mercury, among others) that are deleterious to human health. Herein, we report a novel sulfur-containing small organic dye/sensor naphthoquinodimethyl-bis-thioamide (QDM), which was found to be particularly selective toward mercury ion (Hg2+). Using a combination of UV–vis absorption, photoluminescence, and time-resolved pump–probe techniques, we established that QDM and Hg2+ can form stable complex(es) due to the strong affinity of sulfur toward mercury. In this investigation, while a higher ratio of QDM:Hg2+ was necessary to fully quench the fluorescence emission of QDM, only 1 equiv of the Hg2+ ion was necessary to observe the sensing effect on the excited state photo-behavior(s) of QDM. The present results highlight a synergy between molecular sensors’ selectivity/sensitivity and sensor-analytes dynamics.