Ligand exchange thermochromic systems and high ε ligands for same
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 certain aspects of the present invention, thermochromic systems are disclosed comprising a transition metal ion with particularly useful ligands, such as phosphine compounds, tridentate ligands that coordinate through three nitrogen atoms, bidentate ligands, or ortho hindered pyridine monodentate ligands.
1. A thermochromic system which comprises:
a) a transition metal ion
b) a phosphine compound of the following structure
wherein R 1 , R 2 and R 3 are independently selected from the group consisting of substituted or unsubstituted, straight or branched alkyl, cycloalkyl, substituted or unsubstituted aryl and combinations thereof; wherein heating the system from 25° C. to 85° C. causes an increase in the concentration of a HεMLC formed between the transition metal ion and the phosphine compound.
2. The thermochromic system of claim 1 wherein the thermochromic system additionally comprises iodide.
3. The thermochromic system of claim 1 wherein the transition metal ion is selected from the group consisting of Fe(II), Co(II), Ni(II), Cu(II) and mixtures thereof.
4. The thermochromic system of claim 1 wherein the phosphine compound is selected from the group consisting of ethyldiphenylphosphine, triphenylphosphine, tricyclohexylphosphine and mixtures thereof.
5. The thermochromic system of claim 1 wherein the thermochromic system additionally comprises a diol, a triol, or a polyol.
6. The thermochromic system of claim 1 wherein the thermochromic system additionally comprises a polymer.
7. The thermochromic system of claim 6 wherein the polymer is poly(vinyl butyral-co-vinyl acetate-co-vinyl alcohol).