The synthesis of two novel neutral receptors and their anion binding properties

Two new neutral receptors (1 and 2) containing thiourea and amide groups were synthesized by simple steps in good yields. The binding properties of 1 and 2 with anions were examined by UV-vis, fluorescence, and 1H NMR spectroscopy. Receptor 1 had a better AcO-: H2PO4- selectivity in comparison with that for receptor 2. The association constants of 1·AcO-, 2·AcO-, and 2·H2PO4- were higher in comparison with those of other anions (Cl-, Br-, I-, p-NO2PhO-, and p-NO2PhOPO32-). In particular, a clear color change was observed, from pale yellow to red-brown, upon addition of AcO- to the solution of 1 in DMSO. The UV-vis and fluorescence data indicate that a 1:1 stoichiometry complex is formed between compound 1 or 2 and anions through hydrogen-bonding interactions. (author)