New azo-azomethine receptors, HLn (n=1-3), have been synthesized via condensation reaction of 5-(4-X-phenyl)-azo-salicylaldehyde (X=NO2, Cl and CH3) with (4-Nitrobenzylidene)hydrazine. The receptor with p-NO2 substituent on aromatic ring of azo moiety, HL1, has excellent sensitivity and selectivity towards basic anions with proper discrimination between Fˉ and AcOˉ or H2PO4ˉ in DMSO-water (4:1). Job’s plot displays 1:1 stoichiometry between HL1 and Fˉ alone with 0.737 μM detection limit for fluoride ion. The solvatochromic behavior of HL1 was probed by studying their UV-Vis spectra in four pure organic solvents of different polarities and a meaningful correlation was observed. Furthermore, HL1 was used for detection of inorganic fluoride in toothpaste. The systematic DFT and TD-DFT calculations have been carried out to investigate the mechanism of colorimetric sensing of fluoride ion by HL1 in gas phase and in solution. Moreover, by using F−and H+, as chemical inputs, and the absorbance, as output, a INHIBIT logic gate was constructed, which exhibits “‘Write–Read–Erase–Read” ability without obvious degradation in its optical output.
