Spectral and DFT studies on simple and selective colorimetric sensing of fluoride ions via enhanced charge transfer using a novel signaling unit

Two new colorimetric sensors for fluoride ions [N,N′-(anthracene-9,10-dione-1,2-diyldicarbamothioyl)dibenzamide] and [N,N′-(naphthalene-1,4-dione-2,3-diyldicarbamothioyl) dibenzamide] have been prepared and characterized using various spectral techniques. The quinonoid receptors exhibited high selectivity for fluoride ion detection over other anions. The association constant of the receptor-F complexes were found to be 6.3 × 108 and 7.7 × 1015 M−1 for the anthroquinone and naphthoquionone receptors, respectively. 1H NMR studies indicated that the fluoride ion sensing by the receptors is due to the formation of H-bonds between F-ions and the –NH moiety of the receptors which has been enhanced by directly attaching signaling unit to the receptor unit in the naphthoquinone derivative. The naphthoquinone receptor also exhibited colorimetric sensing of fluoride ions present in commercially available toothpaste samples in aqueous medium. The structural and electronics properties of the sensors and their fluoride complexes were also investigated using ab initio DFT calculations.

► New thiourea based sensor with novel signaling unit was prepared and characterized. ► Simple and selective colorimetric sensing of fluoride ions was demonstrated. ► Qualitative detection of F− ion in commercial toothpaste samples was performed.