Thermodynamics studies of fluorescence quenching and complexation behavior of thallium(I) ion with some polyazamacrocycles

Abstract

The mechanism of fluorescence quenching and stability of the complex formation of thallium(I) ion with polyazamacrocycles [12]aneN 3, Me 3[12]aneN 3, [12]aneN 4, [14]aneN 4, [18]aneN 6 and Me 6[18]aneN 6 were studied in methanol solution at different temperatures spectrofluoromertrically. The factors affecting the mechanism of fluorescence quenching and complexation behavior were found as the size of polyazamacrocycle and substitution of methyl groups on nitrogen atoms of the macrocyclic ring. All the ligands studied form a 1:1 complex at 2.5 × 10 −5 M concentration of the thallium(I) at temperatures 15, 20, 25 and 30 °C. Linear Stern–Volmer plots were obtained for [12]aneN 3, Me 3[12]aneN 3 and [14]aneN 4 (first group). In contrast, in the cases of [12]aneN 4, [18]aneN 6 and Me 6[18]aneN 6 systems (second group) an upward curvature was observed in the corresponding Stern–Volmer plots. From the temperature dependence of the fluorescence quenching, it is demonstrated that the mechanism of the quenching process is probably static for the first group. However, in the case of second group, both the static and dynamic mechanisms contribute to the quenching process of the thallium fluorescence. The formation constants of thallium with groups and thermodynamic parameters Δ H°, Δ S° and Δ G° have been determined and the influence of number of members in macrocycle and the substitution of the methyl groups on nitrogen atoms of the macrocyclic ring on the stability of the complexes is discussed. A green emission was observed for the Tl +-Me 6[18]aneN 6 complex at room temperature.