Color response of tri-armed azo host colorimetric sensors and test kit for fluoride

Five new chromogenic tripodal receptors (2a–e) containing electron withdrawing and donating groups appended to the azophenol moiety were synthesized, characterized, and their chromogenic behaviors toward various anions were investigated. These tripodal receptors showed a distinct color change only when treated with fluoride ions in CH3CN solution. Yet, other anions such as Cl−, Br−, I−, NO3−, ClO4−, AcO−, HSO4−, and H2PO4− could not cause any color change. Thus, the receptors 2a–e can be used as a colorimetric chemosensor for the determination of fluoride ion. In addition, 1H NMR experiments were carried out to explore the nature of interaction between tripodal receptors and fluoride. Finally, analytical application and the use of test strip of the receptor 2b to detect fluoride was also reported.