Synthesis of novel anionic receptors with (thio) urea and amide binding sites and the recognition properties for anions

Two new neutral receptors (1 and 2) containing (thio)urea and amide groups were synthesized by simple steps in good yields. The binding properties for anions of 1 and 2 were characterized by UV-vis and fluorescence spectra. Receptor 1 had an excellent selectivity for AcO^- in comparison with other anions. The association constants of 1 · AcO^- and 2 · p-NO₂PhOPO₃^2- were higher than those of other anions (Cl^-, Br^-, I^-, H ₂PO₄^- and P-NO₂PhO^-). In particular, an obvious color change was observed from light yellow to golden yellow upon addition of AcO^- to the solution of 1 in DMSO. The results of non-linear curve fitting by UV-vis and fluorescence spectral data indicate that a 1:1 stoichiometry complex is formed between compound 1 or 2 and anions through a hydrogen bonding interaction.