Designing of a fluoride selective receptor through molecular orbital engineering

► The molecular orbital engineering in the light of DFT calculations lead to the synthesis of R1. ► The R1 showed selectivity towards fluoride with absorption extending up to NIR region. ► R1 recognized fluoride in a toothpaste sample also. ► The DFT simulations correlated the selectivity in terms of HOMO–LUMO gap nicely. ► The present findings can be helpful in devising new NIR receptors for fluoride. The stepwise substitution of appropriate groups over the 3-[(2,4-dinitro-phenyl)-hydrazono]-butyric acid ethyl ester (R3) lead receptor R1 which showed selectivity towards fluoride in DMSO. The UV–vis and 1H NMR titration studies revealed the details of the binding between receptor R1 and fluoride. The receptor R1 also recognized fluoride in a toothpaste solution to as low as 50ppm. The theoretical simulations of recognition event at Density Functional Theory (DFT) level using B3LYP/6-31G** basis set and polarizable continuum model (PCM) approach lead a semi-quantitative match with the experimental results.