Three chromogenic anionic chemodosimeters (1–3) based on silylated imines were synthesized and characterized. Solutions of compound 1 in acetonitrile with 4.0% (v/v) of water are colorless, but with the addition of several anions only CN⁻, and to a lesser extent F⁻, changed the color of the solutions to orange. However, compounds 2 and 3 were selective toward F⁻ in acetonitrile. The nucleophilic attack of F⁻ or CN⁻ on the silicon center of the chemodosimeters, through an S_N2@Si mechanism, released colored phenolates as leaving groups. PGSE NMR data corroborated the mechanism postulated for the reaction. Kinetics studies were carried out, revealing that a higher second-order rate constant was obtained for the reaction of 1 with F⁻. The addition of water to the system reduces the nucleophilicity of F⁻, showing a slower second-order rate constant in relation to CN⁻, the latter anion being less hydrated and the more reactive species for the nucleophilic attack on the silicon center of 1.