Switching-On Fluorescence by Copper (II) and Basic Anions: A Case Study with a Pyrene-Functionalized Squaramide

The new symmetric acyclic N,N'-bis(1-pyrenyl) squaramide (H) functionalized with the pyrene moiety as a fluorogenic fragment has been designed and its ability to selectively detect specific anions and metals investigated. H selectively binds Cl^- both in solution (DMSO 0.5% H₂O and MeCN) and in the solid state, and allows to selectively detect Cu²⁺ in MeCN with the formation of a 2:1 metal-receptor complex, with a green intense emission appreciable by naked eye under the UV lamp. The H copper complex preserves its emission properties in the presence of Cl^-. The addition of basic anions (OH^-, CN^-, and F^-) up to 10 equivalents caused the deprotonation of the squaramide NHs and a dramatic change of the emission properties of the H copper complex.