A pyrene–calix[4]triazolium conjugate for fluorescence recognition of hydrogen sulfate†

A new fluorescent sensor was developed, in which pyrene is conjugated to calix[4]triazolium via an ester linker, and its ability to bind anions was investigated. Interestingly, addition of HSO₄⁻ to Py-CT4 resulted in increased fluorescence, but other anions had little effect. This phenomenon is attributed to the formation of a 1 : 1 stoichiometric Py-CT4–HSO₄⁻ complex that interferes with the photoinduced electron transfer (PET) process. The selectivity of Py-CT4 for HSO₄⁻ is the result of appropriate spatial complementarity to, and hydrogen bond interaction with, HSO₄⁻. The binding mode and fluorescence changes caused by the PET process can be explained well by density functional theory (DFT) calculations.