Metal-induced conformational change in pyrene-appended calix[4]crown-4 which is useful for metal sensing and guest tweezing

Calix[4]crown (1) bearing an ionophoric cavity on the lower rim and two pyrene groups on the upper rim was synthesized. The metal-binding to the ionophoric cavity changed the distance between two pyrene moieties, which was reflected by a large change in the monomer/excimer fluorescence intensity ratio. This phenomenon was applied to (i) fluorescence sensing of alkali metal cations and (ii) metal-controlled tweezing of a guest (trinitrobenzene). It was shown that the ionophoric cavity can accept only Li⁺ and Na⁺ (Na⁺ > Li⁺) but not at all K⁺.