Azo Dyes Functionalized with Alkoxysilyl Ethers as Chemodosimeters for the Chromogenic Detection of the Fluoride Anion

We have prepared and studied a novel azoic-based colorimetric chemodosimeter (2) which can selectively sense fluoride in acetonitrile-water mixtures, over various other anions by a visible colour change. The mechanism of the chromogenic response arises from a fluoride-hydrolysis of a silyl ether moiety embedded in the chemical structure of the chemodosimeter. Studies on different acetonitrile-water mixtures showed that the fluoride signalling reaction was slower as the amount of water increases. Typical detection times of 15, 40 and 60 min when using 90:10, 75:25 and 50:50 v/v acetonitrile-water mixtures were found. Moreover, although the reactions is slower as the amount of water increases, the method using probe 2 allows to sense fluoride at low concentrations, with detection limits of 0.04, 0.09 and 0.14 ppm in 90:10, 75:25 and 50:50 v/v acetonitrile-water mixtures, respectively. This simple molecule is one of the few probes able to display selective chromogenic sensing features for fluoride in mixed aqueous solutions. Furthermore we have designed and prepared TLC silica foils functionalised by reaction with 3 and have used them to detect fluoride anion in mixed acetonitrile:water solutions