Further the stoichiometry between the PTE-EA (Ligand) and Cu 2+ (metal) complex behind the sensing mechanism was further investigated by using the fluorescence based Job´s plot anaylsis. The graph showed the maximum fluorescence intensity at the mole fraction of 0.5 with skewed peak shape suggesting the stoichiometric ratio of 1:1 between the PTE-EAꓵCu 2+ complex (Figure , ESI).