Design, synthesis, and density functional theory studies of a new selective chemosensor for Pb²

Herein, we have focused on a new colorimetric ligand synthesized from the reaction of 2-hydroxy-5-methylbenzene-1,3-dialdehyde with 2-amino-thiophenol, and investigated its activity as a sensor. In this regard, the sensory activity of the ligand towards different ions (Mn²⁺, Cu²⁺, Co²⁺, Fe²⁺, Fe³⁺, Zn²⁺, Ni²⁺, Cd²⁺, Ag⁺, Na⁺, Cs⁺, Mg²⁺, Al³⁺, Ba²⁺, K⁺, and Pb²⁺) was studied. The specificity of ion bindings is discussed through UV-Vis analysis. The ligand that was synthesized showed remarkable sensitivity, with a detection limit of 0.001 ppb. Additionally, the presence of Pb²⁺ ions can be visually detected through a color change from colorless to yellow. In the last part of this work, we seek to predict the available experimental measurements. Density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) are employed to examine the bonding between the ligand and the Pb²⁺ ion. The effect of water solvent was thoroughly examined for all the steps via the conductor-like Polarizable Continuum Model (CPCM). The theoretical findings revealed that electronic properties, including energy gap, adsorption energy, charge/energy transfer, and optical characteristics, undergo significant changes when Pb²⁺ cations are present. Hence, it can be inferred that the newly synthesized chemosensor (NC) is highly efficient in detecting Pb²⁺.