Design and synthesis of a new organic receptor and evaluation of colorimetric anion sensing ability in organo-aqueous medium

• The receptor R synthesized from the Schiff base condensation reaction of dialdehyde and nitro substituted aminophenol exhibits colorimetric response towards F− and AcO− ion.
• The colour change in organic media allowed spectrophotometric discrimination of fluoride and acetate ions.
• R could successfully detect F− ion in mouthwash with a visible colour change supporting real time applications.
• Detection of F− and AcO− ion was performed in competitive media and quantified with UV-Vis titration studies.
• TD-DFT studies matches well with the experimental data in the binding of anions resulting in a stable receptor-anion complex.
• Lower detection limit of 1.12 ppm was achieved in organic media signifying the role of receptor as a colorimetric anion sensor.

A new organic receptor has been designed and synthesized by the combination of aromatic dialdehyde with nitro-substituted aminophenol resulting in a Schiff base compound. The receptor exhibited a colorimetric response for F− and AcO− ion with a distinct color change from pale yellow to red and pink respectively in dry DMSO solvent and yellow to pale greenish yellow in DMSO:H2O (9:1, v/v). UV–Vis titration studies displayed a significant shift in absorption maxima in comparison with the free receptor. The shift could be attributed to the hydrogen bonding interactions between the active anions and the hydroxyl functionality aided by the electron withdrawing nitro substituent on the receptor. 1H NMR titration and density functionality studies have been performed to understand the nature of interaction of receptor and anions. The lower detection limit of 1.12 ppm was obtained in organic media for F− ion confirming the real time application of the receptor.

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