Anionic fluororeceptors based on thiourea and hydrazide: Synthesis and recognition properties

Two new neutral receptors (1 and 2) containing thiourea and hydrazide groups were synthesized by simple steps in high yields. The binding properties of 1 and 2 for various anions were characterized by UV-Vis and fluorescence spectra. Receptor 1 had a good selectivity for AcO^- in comparison with other anions. The association constants of 1·AcO^- and 2·p-NO₂PhO^- were greater than those of other anions (H₂PO₄^-, Cl^-, Br^- and I^-). In particular, an obvious color change from light yellow to orange-red was observed upon addition of AcO^- to the solution of 1 in DMSO. The results of nonlinear curve fitting by fluorescence spectral data indicate that a complex of 1:1 stoichiometry is formed between compound 1 or 2 and the anions through hydrogen-bonding interaction.