Highly selective colorimetric and reversible fluorometric turn-off sensors based on the pyrimidine derivative: mimicking logic gate operation and potential applications

Abstract

Two novel pyrimidine based 5-(2-hydroxybenzylideneamino)-6-amino-2-mercaptopyrimidin-4-ol (S₁) and 5-(3-nitrobenzylideneamino)-6-amino-2-mercaptopyrimidin-4-ol (S₂) receptors have been synthesized and characterized by various techniques. Both receptors showed 2 : 1 complexation stoichiometry with Ni(II) having binding constants 2.9 × 10⁶ (S₁) and 2.1 × 10⁶ (S₂) calculated by the Job's plot based on the UV-Vis absorption studies. The binding stoichiometry was also supported by the ESI mass spectra and NMR titration. The addition of Ni(II) to both chemosensors, S₁ and S₂ leads to the fluorescence quenching of S–Ni(II), forming an off sensing type system with the limits of detection 33 μM and 48 μM respectively. It was observed that S₁ and S₂ achieved electrochemical changes in reduction and oxidation potentials after the addition of the nickel metal ion. DFT calculations have revealed that the energy gap between the HOMO and LUMO of S₁ and S₂ has significantly decreased upon coordination with Ni(II) in the gas phase.