Multiple target chemosensor: A fluorescent sensor for Zn(II) and Al(III) and a chromogenic sensor for Fe(II) and Fe(III)

A multifunctional fluorescent and colorimetric chemosensor 1, based on two julolidine moieties as a binding and signaling unit, has been synthesized in a one-step procedure. Receptor 1 showed prompt responses toward Zn²⁺ and Al³⁺ ions through selective fluorescence enhancement in dimethylformamide (DMF), while the presence of 5% water made 1 detect only Zn²⁺. Moreover, with 1 the "naked eye" could sense iron by a clear color change. Upon the addition of Fe²⁺ and Fe³⁺ into each solution of 1, the color of the solutions changed from pale yellow to dark green for both Fe²⁺ and Fe³⁺. The binding modes of the complexes were determined to be a 1 : 1 complexation stoichiometry from a Job plot, ¹H NMR titration and ESI-mass spectrometry analysis.