A new approach to design ratiometric fluorescent probe for mercury(II) based on the Hg(2+)-promoted deprotection of thioacetals.

On the basis of the protection reaction between ethanethiol and aldehyde, we designed and synthesized two new ratiometric fluorescent chemosensors, 3 and 4, by using intramolecular charge transfer (ICT) as a signaling mechanism. Upon the addition of Hg(2+) ion, both probes displayed apparent luminescence color changes, which could be observed by naked eyes under a UV lamp. Unexpectedly, both chemosensors also gave response to the addition of trace silver ions, making this kind of chemosensors as the first example of ratiometric fluorescent probe that showed dual channel fluorescence for both Hg(2+) and Ag(+). The test strips experiments suggested that 3 and 4 could serve as practical fluorescent probes for rapid detection of Hg(2+) ion.