A colorimetric chemosensor for fluoride ions based on an indigo derivative

A novel indigo derivative (1) was synthesized and fully characterized. Its structure, confirmed by X-ray crystallography, showed that compound 1 is a planar molecule. Interestingly, compound 1 only has response to fluoride ions among six different anions (F−, Cl−, Br−, I−, AcO−, and HSO4−) in an anhydrous methylene chloride solution and this response can be detected by the ‘naked eyes’.