Ratiometric nanomolar detection of Cu2+ ions in mixed aqueous media: a Cu2+/Li+ ions switchable allosteric system based on thiacalix[4]crown

A novel ditopic fluorescent chemosensor 2, based on the 1,3-alternate conformation of thiacalix[4]crown possessing two complexation sites, was synthesized and shows ratiometric nanomolar detection of Cu2+ ions and exhibits negative allosteric behaviour between Cu2+/Li+ ions in mixed aqueous media.