C3v-symmetric anion receptors with guanidine recognition motifs for ratiometric sensing of fluoride

Abstract

Two new tripodal receptors 3 and 4 derived from a trindane framework having guanidine groups acting as hydrogen bond acceptors are synthesized and characterized for the selective recognition of anions. The anion recognition ability of the receptors was evaluated by UV-vis absorption, fluorescence and ¹H NMR methods. Both the receptors showed F⁻ selective ratiometric chromogenic and fluorogenic responses among the tested anions due to the host–guest complexation followed by the abstraction of the amide-NH protons supported by the ¹H NMR titration study. Receptor 4 with the naphthalene fluorophore units showed higher F⁻ selectively than the receptor 3 by giving visually detectable blue fluorescence and significant turn-on fluorescence at 410 nm which can be switched back and forth by successive addition of F⁻ and H⁺. Further, the reversible and reproducible fluorescence state of 4 can be applied to design a molecular-scale sequential memory unit displaying “Write–Read–Erase–Read” functions in the form of binary logic.