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Abstract
In this communication, we wish to report the design, synthesis and real life applications of coumarin based “naked eye” artificial receptor for fluoride ion detection in aqueous media. Amongst easy-to-synthesize 1-(1-(substituted-2-oxo-2H-chromen-3-yl)-ethylidene)-thiosemicarbazide (receptors A-E), receptor B exhibited remarkable colour change from yellow to pink instantly upon addition of fluoride salt (sodium fluoride) 1×10-5 M (0.19 ppm), in aqueous media. Interestingly, receptor B also gave distinct and discernible colour changes perceivable even with naked eye at different fluoride ion (sodium salt) concentrations (viz., <1.5, 1.5–5 and >5 ppm) fluoride in water which allows a semi-quantitative data to be generated for fluoride contaminated drinking water. Preliminary investigation with everyday commodity items like toothpaste and mouthwash clearly show visual colour change, which may be helpful for detecting presence of fluoride in these items. This method is so simple that it has the potential for being developed as a tool for detecting different levels of fluoride in ground water, especially suitable for rural areas, where the literacy rate is low. The working pH range of receptor B was found to be 6.5–7.5. The binding constant of receptor for fluoride ion was found to be 1.38×105 M-1.