Selective Detection of Hg2+ Ion with Boron Dipyrromethene-Based Fluorescent Probes Appended with a Bis(1,2,3-triazole)amino Receptor.

By using copper-promoted alkyne-azide cycloaddition reaction, two boron dipyrromethene (BODIPY) derivatives bearing a bis(1,2,3-triazole)amino receptor at the meso position were prepared and characterized. For the analogue with two terminal triethylene glycol chains, the fluorescence emission at 509 nm responded selectively toward Hg2+ ion, which greatly increased the fluorescence quantum yield from 0.003 to 0.25 as a result of inhibition of the photoinduced electron transfer (PET) process. By introducing two additional rhodamine moieties at the termini, the resulting conjugate could also detect Hg2+ ion in a highly selective manner. Upon excitation at the BODIPY core, the fluorescence emission of rhodamine at 580 nm was observed and the intensity increased substantially upon addition of Hg2+ ion due to inhibition of the PET process followed by highly efficient fluorescence resonance energy transfer (FRET) from the BODIPY core to the rhodamine moieties. The Hg2+-responsive fluorescence change of these two probes could be easily seen by naked eye. The binding stoichiometry between the probes and Hg2+ ion in CH3CN was determined to be 1:2 by Job' plot and 1H NMR titration, and the binding constants were found to be (1.2 ± 0.1)×1011 M-2 and (1.3 ± 0.3)×1010 M-2, respectively. The overall results suggest that these two BODIPY derivatives can serve as highly selective fluorescent probes for Hg2+ ion. The rhodamine derivative makes use of a combined PET-FRET sensing mechanism which can greatly increase the sensitivity of detection.