The design and synthesis of chemosensors that allows the selectively detection of heavy metal cations by complexation, is an area of ​​growing interest. The hydrazone functional group has been widely used in supramolecular chemistry due to its complexing capacity, its conjugated electrons and its simple methods of synthesis. In this way, a nitrogen system derived from the condensation of vanillin (aromatic aldehyde) and 2-hydrazino benzothyazol to give the corresponding hydrazone for the detection of Cu²⁺ was developed. Spectroscopic determinations demonstrate whether the complexing took place. The hidrazone showed a response in UV-vis spectroscopy and a color shift is observed with the naked eye. In addition, theoretical analysis based on the density functional theory (DFT) was realized. The geometries of the benzothiazole hydrazone derived from vanillin (ligand) and its analog Cu²⁺-ligand complex were optimized at the B3LYP/631+G(d,p) level of theory. The adsorption spectra of this molecular system were analyzed and compared with experimental data. Theoretical study of the structural, electronics and optical properties allowed to understand the chemical changes that the ligand suffers in the complexation process with the Cu⁺² ion.