A new ditopic ratiometric receptor for detecting zinc and fluoride ions in living cells

Abstract

The synthesis, characterization and ion binding properties of a new ditopic ratiometric receptor (1), based on 2-(4,5-dihydro-1H-imidazol-2-yl)phenol and crown ether moieties, have been described. The ditopic ratiometric receptor has been studied in sensing both F⁻ and Zn²⁺ ions, exhibiting different fluorescent colour changes from cyan green to blue/black observable by the naked eye under UV-light. The addition of Zn²⁺ to the solution of 1 induced the formation of a 2 : 2 ligand–metal complex 1–Zn²⁺, which displays a remarkable blue shift of the emission maxima of 1 from 455 nm to 400 nm due to the inhibition of excited-state intramolecular proton transfer (ESIPT) mechanism. The sensing processes were monitored by fluorescence/absorption titrations, and further confirmed by Job's plot and ¹H NMR titrations. The crystal structure of 1–Zn²⁺ reveals that 1 binds Zn²⁺ in four-coordinated modes. Furthermore, 1 is cell permeable and may be applied to detect trace Zn²⁺ and F⁻ during the development of a living organism.