Synthesis and coordination properties of an azamacrocyclic Zn(II) chemosensor containing pendent methylnaphthyl groups

The synthesis of a polyazamacrocycle constituted by two diethylenetriamine bridges functionalized at their central nitrogen with naphth-2-ylmethyl units and interconnected through 2,6-dimethylpyridine spacers (L1) is reported. The protonation behaviour of the new macrocycle in water and in water-ethanol 70/30 v/v mixed solvent has been examined by means of pH-metric, UV-Vis and steady-state fluorescence techniques. The fluorescence emission is slightly quenched following the deprotonation of the central tertiary amines and more deeply quenched upon deprotonation of the secondary amino groups. pH-Metric titrations show that in water-ethanol 70/ 30 v/v L1 forms stable mononuclear complexes with the divalent transition and post-transition metal ions Mn2+, Fe2+, Co2+, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+. In the case of Cu2+, Zn2+, Hg2+ and Pb2+, formation of binuclear complexes has also been observed. Steady-state fluorescence emission studies show that while interaction with Cu2+ leads to quenching of the fluorescence emission above pH = 2, interaction with Zn2+, Cd2+, Hg2+ and Pb2+ give rise to enhancements of the fluorescence above pH ca. 5, which is particularly noticeable in the case of Zn2+.