Tuning the selectivity/specificity of fluorescent metal ion sensors based on N2S2 pyridine-containing macrocyclic ligands by changing the fluorogenic subunit:: Spectrofluorimetric and metal ion binding studies

Two new fluorescent chemosensors for metal ions have been synthesized and characterized, and their photophysical properties have been explored; they are the macrocycles 5-(2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L-5)and 5-(5-chloro-8-hydroxyquinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L-6). Both systems have a pyridyl-thioether-containing 12-membered macrocycle as a binding site. The coordination properties of these two ligands toward Cu-II, Zn-II, Cd-II, Hg-II, and Pb-II have been studied in MeCN/H2O (1:1 v/v) and MeCN solutions and in the solid state. The stoichiometry of the species formed at 25 degrees C have been determined from absorption, fluorescence, and potentiometric titrations. The complexes [CuL5](ClO4)(2)center dot(1)/2MeCN, [ZnL5(H2O)](ClO4)(2), [HgL5(MeCN)](ClO4)(2), [PbL5(ClO4)(2)], [Cu-3(5-Cl-8-HDQH(-1))((LH-1)-H-6)(2)](ClO4)(3)center dot 7.5H(2)O (HDQ = hydroxyquinoline), and [Cu(L-6)(2)](BF4)(2)center dot 2MeNO(2) have also been characterized by X-ray crystallography. A specific CHEF-type response of L-5 and L-6 to the presence of Zn-II and Cd-II, respectively, has been observed at about pH 7.0 in MeCN/H2O (1:1 v/v) solutions.