Sensing of Co²⁺ and Cu²⁺ Ions Using Dimethylamino-functionalized Poly(azomethine-1,3,4-oxadiazole)s

The ability of OxT and OxFl azomethines to recognize metal ions in THF solutions was investigated using UV-vis absorption techniques. Various metal ions, including Cd²⁺, Hg²⁺, Co²⁺, Sn²⁺, Cu²⁺, Ni²⁺, Zn²⁺ and Ag⁺, were tested. The absorption spectra revealed two distinct π-π* transition bands in the 273–278 nm and 330–346 nm wavelength ranges. Additionally, OxFl displayed an absorption peak at 309 nm, attributed to the fluorene group. Spectral titrations were used to study the fluorescence behavior in the presence of these metal ions. The results showed significant quenching with Co²⁺ and Cu²⁺ ions, while other metal ions had minimal effects on the fluorescence intensity. The quenching mechanism was further analyzed using the Stern-Volmer and Lehrer equations, and the binding constants ( \({\mathrm{K}}_{\mathrm{b}}^{\mathrm{fl}}\) ${\mathrm{K}}_{\mathrm{b}}^{\mathrm{fl}}$ ) were calculated using the Benesi-Hildebrand relations. The results confirm that Co²⁺ has a 1:2 stoichiometry and Cu²⁺ has a 1:1 stoichiometry, indicating the strong affinity of OxFl and OxT for these ions. The negative values of ΔG (Gibbs free energy) suggest that complex formation occurs spontaneously at room temperature.