Simple colorimetric sensors with high selectivity for acetate and chloride in aqueous solution

A series of novel colorimetric anion sensors bearing phenol O–H and hydrazone N–H groups were synthesized and their structures were confirmed by X-ray single-crystal diffraction. In DMSO/H2O (9:1, v/v) solutions, two-arm pincer type sensors 1 and 2 could bind Cl− through the collaboration of phenol O–H and hydrazone N–H groups. In DMSO/H2O (7.5:2.5, v/v) solutions, sensors 1, 2 and 4 showed colorimetric single selectivity for AcO−. When AcO− was added to their solutions, dramatic color changes from orange to magenta were observed. Yet other anions such as F−, Cl−, Br−, I−, HSO4− and H2PO4− could not cause any color change. Comparison with compound 5 (the analogues of 1–4, but not containing the O–H groups) indicates that the phenol O–H group plays a critical role in the anion-recognition process.