New Fluorescent Chemosensors for Heavy Metal Ions Based on Functionalized Pendant Arm Derivatives of 7-Anthracenylmethyl-1,4,10-trioxa-7,13-diazacyclopentadecane

Two new ligands 7-anthracenylmethyl-13-methylpyridyl-1,4,10-trioxa-7,13-diazacyclopentadecane (L4) and 7-anthracenylmethyl-13-(2,2-dimethyl-2-hydroxyethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L5) have been synthesized
and characterized. Both derive from 7-anthracenylmethyl-1,4,10-trioxa-7,13-diazacyclopentadecane (L3) 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 L4, L5, and the unbranched L3 with
metal ions have been studied in MeCN/H2O (1:1 v/v, 298.1 K, I = 0.1 M) using potentiometric methods. The
crystal structures of L3, [(H2L3)(HL3)](ClO4)3, and the complex [CdL3(NO3)2] have been determined by single-crystal
X-ray methods. The fluorescent behavior of L3−L5 in the presence of CuII, ZnII, CdII, HgII, and PbII has been studied
as a function of pH in MeCN/H2O (1:1 v/v). The presence of CuII, HgII, or PbII does not affect the fluorescent
behavior observed for the three free ligands upon changing the pH. Interestingly, the fluorescent emission of L3
and L5 is selectively enhanced only in the presence of CdII at basic pH. The same effect is observed for L4 in the
presence of CdII or ZnII at about pH 7.