This paper will report the design and synthesis of a fluoride-selective colorimetric receptor,N-benzoyl-4-(4'-nitrophenylazo)aniline, 3, in which amide as recognition group was coupled to 4-(4'-nitrophenylazo)aniline (2) of ground-state intramolecular charge transfer character. It was found that 3 had an absorption maximum at 380 nm in acetonitrile, which decreased gradually upon addition of F-. A new band peaked at 530 nm appeared, which turned the solution from light yellow to purplish red. The new band due to the hydrogen bonding complex of 3 with F- was shown to be of charge transfer character by the observation of a substantial red shift with increasing solvent polarity. ¹H NMR titrations confirmed hydrogen bonding interaction between 3 and F-.

Key words: azobenzene, fluoride ion, anion recognition, charge transfer