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

In this work, 5,5′,5′′-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalate (H 6 L) was used as a gelator to prepare thermostable supramolecular gels (H 6 L gels). The lowest critical gelation concentration of H 6 L was found to be only 0.14 wt%. H 6 L gels remained stable after being placed at 85 °C for 1 h, indicating that its gel-sol phase transition temperature ( T gel ) was not<85 °C. H 6 L gels can be formed in just a few seconds in comparison with the longer gelation time of a conventional thermostable gel. Moreover, a thermostable H 6 L/Fe 3+ gel was also prepared by the coordination interactions of H 6 L and Fe 3+ 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 H 6 L gels. In addition, the fluorescence spectra of H 6 L 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 H 6 L 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 H 6 L/Fe 3+ gels.