Synthesis of Colorimetric Sensors for Selective Discrimination Between Maleate and Fumarate

Three new chromogenic receptors (1, 2, and 3) were synthesized and characterized. Upon addition of maleate to receptor 1 in DMSO, the appearance of the solution of receptor 1 showed a color change from dark-blue to dark-red, which can be detected by the naked eye at parts per million. Similar experiments were repeated using 2, the solution showed a distinct color change from blue to green when 2 is formed as a complex with maleate. Whereas, the addition of the same anions to receptor 3, did not induce any color change. On the other hand, when fumarate was added to receptors 1–3, the color of solution changed from dark-blue to bright yellow for receptor 1 and did not induce any color change for receptor 2 and 3. Thus, for unique color change, both receptors 1 and 2 can act as optical chemosensors for recognition of maleate versus fumarate. Especially, receptor 1 has a unique color change for the recognition of fumarate, accordingly it can be used for detection of the fumarate anion.