An anionic chromogenic sensor based on protonated Reichardt’s pyridiniophenolate

An anionic sensor based on Reichardt’s betaine is described here. The dye is blue-green in chloroform but becomes colorless under protonation. Increasing amounts of different anions were added into the solution of the protonated dye. The addition of F⁻ and caused the reappearance of the original blue-green color, while the addition of I⁻ made the solution of the protonated dye yellow. The observations are discussed based on the fact that F⁻ and can act as bases accepting a proton from the protonated dye and also in relation to the formation of a complex between the protonated dye and iodide.