Thermostable fluorescent supramolecular gels constructed from a single gelator and its application in discriminating organic acids

Abstract

In this work, 5,5′,5′′-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalate (H6L) was used as a gelator to prepare thermostable supramolecular gels (H6L gels). The lowest critical gelation concentration of H6L was found to be only 0.14 wt%. H6L gels remained stable after being placed at 85 °C for 1 h, indicating that its gel-sol phase transition temperature (Tgel) was not<85 °C. H6L gels can be formed in just a few seconds in comparison with the longer gelation time of a conventional thermostable gel. Moreover, a thermostable H6L/Fe3+ gel was also prepared by the coordination interactions of H6L and Fe3+ ions. The studies of FT-IR, UV–vis, XRD and SEM reveal that multiple hydrogen bonds, π-π interactions as well as coordination interactions were the main driving forces for the formation of thermostable three-dimensional network structure of H6L gels. In addition, the fluorescence spectra of H6L gels showed that the dual emission at 396 nm and 469 nm was derived from the structure of melamine and 5-aminoisophthalic acid contained in H6L structure. The gel formed at high temperature had relatively high transparency and strong fluorescence signal, and the fluorescence intensity is affected by the external H+ concentration. Using this characteristic, 14 organic acids can be effectively identified with the help of principal component analysis (PCA). L-cysteine can be identified with the naked eye by the color and state changes of H6L/Fe3+ gels.