Synthesis of colorimetric receptors for dicarboxylate anions: a unique color change for malonate

Abstract

Three new chromogenic receptors ( 1 , 2 , and 3 ) containing p-nitrophenyl or p-nitronaphthyl or methyl groups appended to the thiourea groups were synthesized and characterized. Upon addition of a series of dicarboxylate anions to receptor 1 in DMSO, only the appearance of the solution of receptor 1 with malonate showed a color change from blue to yellow which can be detected by the naked eye at parts per million. With the addition of the series of dicarboxylate anions to receptor 2 , the solutions showed an indistinct intense dark-red color. Whereas the addition of the same dicarboxylate anions to receptor 3 , the solutions did not induce any color change. Thus, for the unique color change, the receptor 1 can act as an optical chemosensor for the malonate anion even in the presence of other dicarboxylate anions.