A Selective Ratiometric Receptor 2-((E)-(3-(prop-1-en-2-yl)phenylimino)methyl)-4-nitrophenol for the Detection of...

A Schiff-base 2-((E)-(3-(prop-1-en-2-yl)phenylimino)methyl)-4-nitrophenol (Receptor 1) colorimetric probe was synthesized and its UV-visible and fluorescence spectral properties for the sensing of Cu^+ 2 ions in CH₃OH/H₂O (60:40,v/v) solvent system was explored. The Receptor 1 showed the discriminating spectral behavior with the addition of Cu²⁺ ions solution. The other metal ions showed no significant effect towards Receptor 1. Moreover, the addition of Cu²⁺ ions to the Receptor 1 demonstrated the shift in the peak towards longer wavelength of 405 nm due to the ligand to metal charge transfer (LMCT) effect. The red-shift and new peak at 405 nm are due to the deprotonation of the -OH group and formation of complex and O-Cu covalent bond, respectively. A slight increase in the Cu²⁺ ion concentration exhibited strong absorption and fluorescence properties, leading to the spontaneous change in color from pale yellow to orange. Additionally, Density Functional Theory (DFT) studies were performed to investigate the interaction of Cu²⁺ ions with Receptor 1. The decrease in the energies (3.59062 kcal/mol to 0.36028 kcal/mol) of Cu²⁺-Receptor-1 complex compared to Receptor 1 confirms the strong interaction with high stability. The association constant (Ka) of Cu²⁺-Receptor-1 complex was found as 175000 M^- 1. The limit of detection (LOD) was calculated and noted as 179 nM.