Development of colorimetric receptors for selective discrimination between isomeric dicarboxylate anions

Three new chromogenic receptors (1, 2, and 3) containing p-nitrophenyl or p-nitronaphthyl group appended to the thiourea units or containing p-nitrophenyl group appended to the urea moiety were synthesized and characterized. Upon addition of a series of isomeric dicarboxylate anions to receptor 1 in DMSO/H2O (80:20 v/v), the appearance of the solution of receptor 1 with maleate or phthalate showed color changes from blue to green or blue to dark-green, respectively, which those can be detected by naked eye at parts per million. Similar experiments were repeated using 2, the solution showed a distinct color change from blue to pink only when 2 is formed as a complex with maleate. Whereas, the addition of the same isomeric dicarboxylate anions to receptor 3, did not induce any color change. Thus, for unique color change, both receptors 1 and 2 can act as optical chemosensors for recognition of maleate versus fumarate. In addition, the receptor 1 can also be a colorimetric receptor for selective discrimination between aromatic isomeric dicarboxylate anions.