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

Two novel pyrimidine based 5-(2-hydroxybenzylideneamino)-6-amino-2-mercaptopyrimidin-4-ol (S-1) and 5-(3-nitrobenzylideneamino)-6-amino-2-mercaptopyrimidin-4-ol (S-2) receptors have been synthesized and characterized by various techniques. Both receptors showed 2 : 1 complexation stoichiometry with Ni(II) having binding constants 2.9 x 10(6) (S-1) and 2.1 x 10(6) (S-2) 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, S-1 and S-2 leads to the fluorescence quenching of S-Ni(II), forming an off sensing type system with the limits of detection 33 mu M and 48 mu M respectively. It was observed that S-1 and S-2 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 S-1 and S-2 has significantly decreased upon coordination with Ni(II) in the gas phase.