Colorimetric and highly selective “turn-on” fluorescent anion chemosensors with excited state proton transfer

2-(3-Hydroxy-naphthalen-2-yl)-benzo[d][1,3]oxazin-4-one (HNBO), 3-hydroxy-naphthalene-2-carboxylic acid (2-heptylcarbamoyl-phenyl)-amide (HNAHPA) and 2-[2-(2-hydroxy-phenyl)-benzooxazol-6-ylmethylene]-malononitrile (HBODC) are shown to be fluorescent and colorimetric anion chemosensors with high selectivity for F− over Cl−, in the low analyte concentration range of 10−6 to 10−4 M.