A Novel Calix[4]Crown-Based 1,3,4-Oxadiazole as a Fluorescent Chemosensor for Copper(II) Ion Detection

The synthesis and characterization of a novel florescent chemosensor 1 with two different types of cationic binding sites have been reported in this work, which is a calix[4]crown derivative in 1,3-alternate conformation bearing two 2-phenyl-5-(4-dimethylaminopyenyl)-1,3,4-oxadiazole units. The recognition behaviors of 1 in dichloromethane/acetonitrile solution to alkali metal ions (Na⁺ and K⁺), alkaline earth metal ions (Mg²⁺ and Ca²⁺), and transition metal ions (Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Cu²⁺, Mn²⁺, and Ag⁺) have been investigated by UV-Vis and fluorescence spectra. The fluorescence of 1 might be quenched selectively by Cu²⁺ due to the photo-induced electron transfer mechanism, and the quenched emission from 1 could be partly revived by the addition of Ca²⁺ or Mg²⁺; thus, the receptor 1 might be worked as an on-off switchable fluorescent chemosensor triggered by metal ion exchange.