Luminescence sensitization of terbium-loaded supramolecular gels by hydroxybenzoic acids and used for salicylates sensing.

The luminescent terbium (Tb3+)-loaded supramolecular gels were facilely prepared through the self-assembly of Fmoc-diphenylalanine (FmocPhePhe) at room temperature. Hydroxybenzoic acid (HA, the isomers are denoted as 2-HA, 3-HA, and 4-HA depending upon the positions of hydroxyl groups) was used as a sensitizer to Tb3+. The luminescence sensitization of Tb3+ in the gels was realized by the coordination with hydroxybenzoic acids. The spectra of luminescence, UV-vis, FT-IR, and 1H NMR verified that this sensitization was attributed to the energy transfer from hydroxybenzoic acids to Tb3+. The results of XRD, SEM, and phase transfer temperature further indicated that the initial molecule arrangement of the gels was significantly changed by 2-HA, resulting in more ordered and more compact morphology of the gels. 2-HA exhibited more effective sensitization to Tb3+ in the gels than 3-HA and 4-HA. It was also found that 2-HA did not affect the self-assembly of FmocPhePhe. Due to the effective fluorescence sensitization by 2-HA, the as-prepared gels can be used for salicylic acid sensing with 6.8 μM of the detection limit. This strategy has been successfully used for the detection of salicylates in pharmaceuticals and cosmetics.