Ligand exchange of thermochromic, LETC, systems exhibiting a reversible change in absorbance of electromagnetic radiation as the temperature of the system is reversibly changed are described. The described LETC systems include one or more than one transition metal ion, which experiences thermally induced changes in the nature of the complexation or coordination around the transition metal ion(s) and, thereby, the system changes its ability to absorb electromagnetic radiation as the temperature changes.In accordance with one aspect of the present invention, a thermochromic device is disclosed comprising at least two thermochromic layers when each thermochromic layer includes a polymer, at least one transition metal ion, at least one H.epsilon.L ligand capable of forming a H.epsilon.MLC with the transition metal ion and at least one L.epsilon.L ligand capable of forming an L.epsilon.MLC with the transition metal ion. In accordance with yet another aspect of the present invention, the thermochromic device further includes a separator between the first and second thermochromic layers to prevent intermixing of the contents of the layers.