Fluorescent ligands have been designed to form ternary complexes with a Cu-II cation and phosphates in a buffer solution at physiological pH 7.4. It has been shown that a combination of two different ligands and CuCl2 allows one to achieve high adenosine triphosphate/adenosine diphosphate, adenosine 5'-monophosphate selectivity, and ratiometric fluorescence sensing, while separately each ligand complex does not have such properties.