Chromotropism is defined as a reversible color change of the materials caused by the surrounding chemical or physical stimulus; the stimuli could be solvent (solvatochromism), temperature (thermochromism), pressure (piezochromism), light (photochromism), pH (halochromism), ion (ionochromism) or electrons (electrochromism). Chromotropism has attracted much attention because of the wide variety of potential applications as thermosensitive materials, imaging, photo-switching materials, sensor materials, molecular switches, pollutant sensors and Lewis-acid-base color indicators. A combination of metal-ion recognition moieties with appropriate ligands has been reported to afford metal-ion responsive chromotropic molecules. Among chromotropic metal complexes, copper (II) ion with a combination of chelate ligands have been recognized as the most promising candidates for practical applications due to their high thermodynamic stabilities, accessibility of other oxidation states and also existence of simple and regular changes in their electronic spectra according to the strength of the stress imposed to the system. Here, a series of mono and dinuclear copper(II) complexes with chelating ligand of 2-methyl-N-(pyridine-2-yl-methyl)propane-2-amine, in which demonstrated distinctive solvato- and theromo- iono and halochromism properties is presented. The mechanism of the chromotropism in these compounds is discussed in detail.
