Excited-state intramolecular proton transfer-based covalent organic framework for fluorescence anion sensing

An azine-linked covalent organic framework, ACOF, has been prepared via the reaction of hydrazine hydrate and an aldehyde group building unit with a hydroxyl group in situ under solvothermal conditions. ACOF possesses good porosity, remarkable stability, and excellent luminescence. Specifically, the excited-state intramolecular proton transfer (ESIPT) strategy occurs in the skeleton of ACOF containing hydroxyl groups (intramolecular proton donor) and imine bonds (proton acceptor) to induce phototautomerization, which further affords excellent luminescence. Interestingly, ACOF exhibits high sensitivity and excellent selectivity towards fluoride anion detection by the interaction of fluoride anions and hydroxyl groups, which interrupts ESIPT to turn off fluorescence.