Rational design of fluorescent probe for Hg 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 ions and other various metal ions in organic and water solutions are studied in detail absorption and emission spectroscopy. All these probes show a selective "on-off-type" fluorescent response to Hg ions in solution over other metal ions with a maximum detection limit of 10 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 are studied in detail 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 fluorescent probes.