New fluorescent chemosensors for heavy metal ions based on functionalized pendant arm derivatives of 7-anthracenylmethyl-1,4,1 0-tri oxa-7,1 3-diazacyclopentadecane

Two new ligands 7-anthracenylmethyl-13-methylpyridyl-1,4,10-trioxa-7,13-diazacyclopentadecane (L-4) and 7-anthracenylmethyl-13-(2,2-dimethyl-2-hydroxyethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L-5) have been synthesized and characterized. Both derive from 7-anthracenylmethyl-14,10-trioxa-7,13-diazacyclopentaclecane (L-3) and differ for having a differently functionalized pendant arm covalently attached to the remaining secondary nitrogen donor of the macrocyclic framework. The protonation and coordination behavior of L-4, L-5, and the unbranched L-3 with metal ions have been studied in MeCN/H2O (1:1 v/v, 298.1 K, / = 0.1 M) using potentiometric methods. The crystal structures of L-3, [(H2L3) (H2L3)] (ClO4)(3), and the complex [CdL3(NO3)(2)] have been determined by single-crystal X-ray methods. The fluorescent behavior of L-3-L-5 in the presence of Cu-II, Zn-II, Cd-II, Hg-II, and Pb-II has been studied as a function of pH in MeCN/H2O (1:1 v/v). The presence of Cu-II, Hg-II, or Pb-II does not affect the fluorescent behavior observed for the three free ligands upon changing the pH. Interestingly, the fluorescent emission of L-3 and L5 is selectively enhanced only in the presence of Cd-II at basic pH. The same effect is observed for L-4 in the presence of Cd-II or Zn-II at about pH 7.