chromotropic properties

New complexes, [LCuX2] (X = Br or Cl) and [LZnCl2], incorporating the N-(pyridin-2-ylmethyl)butan-2-amine ligand (L), were successfully synthesized and characterized. The complexes were obtained in high yield through a straightforward reaction between the ligand and metal halide. Detailed characterization using FT-IR, UV-Vis spectroscopy, thermogravimetric analysis (TGA) and the density functional theory (DFT) calculation confirmed the coordination of ligand to the copper(II) center and revealed distorted square planar geometry of the complexes. [LCuBr2] complex exhibited a notable solvatochromic effect, with its solution changing color from green to blue-green depending on the polarity of the solvent. This phenomenon was attributed to solvent molecules interacting with the vacant axial sites of the copper center along with the structural changes. Additionally, the complex displayed halochromism in aqueous solution, where the d-d transition band shifted to higher energy with increasing pH due to the deprotonation of the secondary amine group of the ligand.Furthermore, the complex demonstrated thermochromism in high-boiling-point solvents such as DMSO and DMF. Upon heating, the solution changed color from green to blue, likely due to substituting coordinated bromide/chloride with solvent molecules. This process was reversible upon cooling, highlighting the thermoresponsive nature of the complex. Moreover, the complex exhibited selective ionochromic behavior towards the azide anion (N3-), displaying a distinct color change in the presence of other pseudo-halide anions. This suggests potential applications as a sensor for this specific anion.