Fluorescent calix[4]triazole for selective fluoride anion sensing

Fluoride ions (F^-) play an important role in preventing cavities and treating osteoporosis, but excessive exposure can lead to serious health problems such as fluorosis and kidney damage. These dual characteristics highlight the need for selective and sensitive methods to detect fluoride ions for health monitoring. Accordingly, in this study, we investigated the anion-binding ability of Py-CT4, a fluorescent chemosensor in which pyrene is linked to calix[4]triazole via an ester linker. Notably, Py-CT4 exhibited significant fluorescence quenching for F^- compared to other anions, and its fluorescence intensity gradually decreased with increasing F^- concentration. This phenomenon is driven by electron transfer from calix[4]triazole to pyrene, initiated by hydrogen bonding with F^- and followed by F^--induced deprotonation of calix[4]triazole. The selectivity of Py-CT4 for F^- appears to stem from its relatively flexible structure and low acidity compared to the previously reported Py-CT4+. Py-CT4 thus represents the first macrocyclic receptor based on charge-neutral 1,2,3-triazole that selectively recognizes F^- through fluorescence quenching. Compared to traditional detection methods, Py-CT4 utilizes the advantages of fluorescent detection, such as higher sensitivity, faster response times, and ease of use, for fluoride ion detection. Py-CT4 also demonstrates excellent selectivity for F^- even in the presence of competing anions. These features make Py-CT4 a promising tool for monitoring fluoride ions in biological and environmental systems, providing valuable insights into public health and safety.