A luminescent dimer as a turn-off sensor for both nitrite anion and ferric cation

The cation and anion recognition properties of a binuclear Eu(III) complex, [Eu₂(μ₂-η²-H₂L)₂(μ₂-H₂L)₂(phen)₂(NO₃)₂]⋅2CH₃OH (EuL′) {H₃L = 2-(3-benzoylthioureido)ethanoic acid; phen = 1,10-phenanthroline} have been thoroughly investigated in DMF solution at room temperature by luminescence method. These investigations revealed that the EuL′ dimer acts as a bifunctional ‘turn off’ sensor for both Fe³⁺ cation and anion. The possible luminescence quenching mechanism of Fe³⁺ cation and anion to the dimer has been discussed. Furthermore, the simple and portable test paper based on the EuL′ fluorescent sensor has been explored, which may provide a convenient method of determination of Fe³⁺ and ions in everyday applications.