Ultrasound-accelerated organogel: application for visual discrimination of Hg(2+) from Ag(+)

A new kind of naphthalimide-based organogelator, TN, was designed and synthesized. The intramolecular guanylation of TN promoted by Hg(2+) or Ag(+) in both solution and gel state was studied through several approaches including FL, UV-visible, NMR, FT-IR and SEM experiments. TN could selectively sense Hg(2+) and Ag(+) ions with obvious fluorescence quenching and color changes from yellow to colorless among test ions in the solution state. Interestingly, the S-gel of TN could be used to selectively discriminate Hg(2+) from Ag(+)via phase and morphology changes. Hg(2+) ions triggered the gel-to-gel transition with morphology changes of the TN S-gel from nanofibrils to porous sheet structure, together with fluorescence quenching. In contrast, the gel collapsed in the presence of Ag(+) ions, which was comprised of short and disordered fiber structure. To the best of the authors' knowledge, this is the first example of gels selectively sensing Hg(2+) or Ag(+)via a reaction approach.