The Design of a Highly Selective Fluorescent Chemosensor for Cu(II) within Wide pH Region and a Molecular Switch Controlled by pH

A new calix[4]arene-based fluorescent compound with two thio-ether groups as ionophore and one 3-alkoxy-2-naphthoic acid moiety as fluorophore has been designed, which exhibited highly selective binding of Cu 2+ over alkali, alkaline earth and some transition metal ions, including Co 2+, Ni 2+, Zn 2+, Mn 2+, Cd 2+, Pb 2+, Hg 2+, Ag +, Cu +, in CH 3OH–H 2O (2:1) within wide pH region. Moreover, the change of pH induces the consecutive quenching/revival of the fluorescence, with a concomitant distinct difference of the fluorescence quantum yield. In consequence, this system could be considered as a molecular switch.