Rational design of fluorescent probe for Hg(2+) by changing the chemical bond type

Two kinds of fluorescent probes DFBT and DFABT, and their corresponding water-soluble compounds WDFBT and WDFABT, based on the trimers containing a benzo[2,1,3]thiadiazole moiety and two fluorene moieties are synthesized. Their luminescent behavior towards Hg(2+) ions and other various metal ions in organic and water solutions are studied in detail via absorption and emission spectroscopy. All these probes show a selective “on–off-type” fluorescent response to Hg(2+) ions in solution over other metal ions with a maximum detection limit of 10(−7) M. Importantly, the probe type can be changed from irreversible to reversible by altering the bridge mode between the functional units from C[triple bond, length as m-dash]C triple bond to C–C single bond. Their detection mechanisms towards Hg(2+) are studied in detail via mass spectrometry and Job plots, which are attributed to irreversible chemical reaction for DFABT and WDFABT and a reversible coordination reaction for DFBT and WDFBT respectively. Our research results about this kind of organic fluorescent probe provide valuable information to the future design of practical Hg(2+) fluorescent probes.