Azobenzene-based colorimetric chemosensors for rapid naked-eye detection of mercury(II)

Two new highly selective colorimetric chemosensors for Hg(2+), based on azobenzene and highly selective Hg(2+)-promoted deprotection of a dithioacetal have been designed and synthesized. In the presence of as little as 20 μM Hg(2+), the sensors change their color from light yellow to deep red, which can easily be observed by the naked eye. The underlying signaling mechanism is intramolecular charge transfer (ICT). The sensors have good selectivity for Hg(2+) with respect to several common alkali, alkaline earth, and transition metal ions. Furthermore, they can be used for in-the-field measurements by virtue of a dipstick approach without any additional equipment.