Aminothiophenol and 7-diethylamino-4-hydroxycoumarin derived probe for reversible turn off-on-off detection of Cu2+ ions and cysteine

Here, we present a simple disulfide linked probe HTP for rapid detection of Cu2+ ions, which was prepared by a condensation reaction between 7-diethylamino-4-hydroxycoumarin aldehyde and 2-aminothiophenol. The disulfide linked probe HTP was characterized using 1H NMR, 13C NMR, and HRMS spectroscopic analysis and confirmed by single crystal X-ray diffraction analysis. The photophysical behavior of HTP in various solvents (non-polar to polar) was studied and HTP displayed aggregation induced emission (AIE) characteristics in CH3CN-water mixtures (0-99 %). Upon binding with Cu2+ ions, emission enhancement occurs along with color changes from weak green to intense yellow emission in CH3CN/Tris-HCl buffer (20 mu M, 9:1, 10 mM Tris HCl Buffer, pH = 7.4). Detection limit for Cu2+ ions was found to be 0.97 nM which is lower than the recommended tolerance limit by the WHO and the association constant 0.42 x 108 M- 1 was obtained using B-H plot. Furthermore, the stoichiometric ratio 1:1 was confirmed by Job's plot, 1H NMR, mass spectral analysis and DFT calculations were supported the formation of HTP-Cu2 & thorn; complex. The reversibility of HTP with Cu2+ ions was achieved by cysteine with detection limit and association constant value of 1.64 mu M and 0.15 x 107 M- 1 respectively. The reversible sensing nature of HTP with Cu2+/cysteine was further applied for constructing a molecular logic gate (INHIBIT) and practical applications such as paper strips, cotton swabs and real water analysis.