A highly selective and sensitive fluorescent chemosensor for Hg2+ based on a pyridine-appended π-conjugated ligand

A pyridine-appended pi-conjugated ligand 1,4-bis[2-(4-pyridyl)ethenyl]benzene (bpeb) has proved to be highly selective and sensitive as a chemosensor for Hg2+ in buffered aqueous solution. Remarkable changes in the UV-vis and fluorescence emission spectra were observed upon addition of Hg2+ ions to a solution of bpeb. In particular, the interaction of the lone-pair electrons on the pyridine nitrogen with Hg2+ ions results in a significant red-shift in the fluorescence spectrum and a large Stokes shift of up to 65 nm. DFT calculations have revealed that the energy levels of the HOMO and LUMO of bpeb are critically decreased upon coordination to Hg2+ ions, thereby accounting for this red-shift of the fluorescence spectrum. Furthermore, bpeb has been shown to be applicable as a fluorescent probe for imaging Hg2+ ions in PC3 cell lines, which may help in the understanding of relevant biological processes at the molecular level.