Ligand exchange thermochromic, (LETC), systems
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.
1. A thermochromic system comprising:
a) Co(II)
b) a first ligand comprising a diol, a triol or a polyol;
c) a second ligand comprising an oxygen containing ligand or a sulfur-containing ligand, wherein the second ligand is capable of coordinating to a transition metal ion through oxygen or sulfur;
wherein the system has a reversible, net increase in its ability to absorb light energy in the 400 nm to 1400 nm range due to an increase in concentration of a coordination compound between Co(II) and the second ligand as the temperature of the system is increased.
2. The thermochromic system of claim 1 , wherein the second ligand comprises a phosphinate anion, a carboxylate anion, or a thiophosphinate anion.
3. The thermochromic system of claim 2 , wherein the anion is a phosphinate anion selected from the group consisting of anions of the following structure and mixtures thereof:
wherein R and R′ are independently selected from the group consisting of optionally substituted, straight and branched chain alkyl, aralkyl, aryl, substituted aryl and combinations thereof.
4. The thermochromic system of claim 2 , wherein the second ligand comprises the phosphinate anion provided as salts of alkali metal cations, quaternary ammonium cations or quaternary phosphonium cations.
5. The thermochromic system of claim 4 , wherein the phosphinate anion is selected from the group consisting of bis(hydroxymethyl)phosphinate, bis(4-Methoxyphenyl)phosphinate, methylphenylphosphinate, diphenylphosphinate, dimethylphosphinate and mixtures thereof.
6. The thermochromic system of claim 2 , wherein the second ligand comprises the thiophosphinate anion.
7. The thermochromic system of claim 2 , wherein the second ligand comprises the carboxylate anion.
8. The thermochromic system of claim 7 , wherein the carboxylate anion is selected from the group consisting of acetate, trifluoroacetate, benzoate 2-methoxybenzoate, salicylate malonate, succinate, phthalate and mixtures thereof.
9. The thermochromic system of claim 1 , wherein the second ligand comprises a phosphine oxide or a phosphine sulfide.
10. The thermochromic system of claim 9 , wherein the phosphine oxide is selected from the group consisting of hexamethylphosphoramide, tributylphosphine oxide, triphenylphosphine oxide and mixtures thereof.
11. The thermochromic system of claim 1 , wherein the second ligand comprises a nitrate anion, a pyridine-N-oxide or a phenolate anion.
12. The thermochromic systems of claim 1 , wherein the first ligand is represented by the following structure:
wherein R is selected from the group consisting of H, alkyl, substituted alkyl, branched alkyl, aralkyl, aryl, amino, substituted amino, nitro and combinations thereof.
13. The thermochromic system of claim 12 , wherein the first ligand is selected from the group consisting of trimetholmethane, trimethylolethane, trimethylpropane, trimethylolbutane, pentaerythritol, di-pentaerythritol, trimethyloInitromethane, trimethylolaminomethane and mixtures thereof.
14. The thermochromic systems of claim 1 , wherein the first ligand is represented by the following structure:
wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are independently selected from the group consisting of H, straight, branched, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl and combinations thereof; provided that optionally any combination of two or more of R 1 , R 2 , R 3 , R 4 , R 5 and/or R 6 may be joined together to form one or more optionally substituted ring systems.
15. The thermochromic system of claim 14 , wherein the first ligand is a diol ligand selected from the group consisting of 1,3-Cyclohexanediol; 1,1-Bis(hydroxymethyl)cyclopropane; 2,2-Bis(hydroxymethyl)propionic acid; 2,2-Dibutyl-1,3-propanediol; 2,2-Diethyl-1,3-propanediol; 2,2,4-Trimethyl-1,3-pentanediol; 2,4-Dimethyl-2,4-pentanediol; 2,4-Pentanediol; 2-Bromo-2-nitro-1,3-propanediol; Serinol; 2-Butyl-2-Ethyl-1,3-propanediol; 2-Ethyl-1,3-hexanediol; 2-Methyl-1,3-propanediol; 2-Methyl-2,4-pentanediol; 2-Methyl-2-propyl-1,3-propanediol; 2-Methylenepropane-1,3-diol; 2-Phenyl-1,3-propanediol; Cyclohex-3-ene-1,1-diyldimethanol; 3-Methyl-1,3-butanediol; 3-Methyl-2,4-heptanediol; [2-(2-phenylethyl)-1,3-dioxane-5,5-diyl]dimethanol; Neopentyl Glycol; Trimethylolpropane allyl ether and mixtures thereof.
16. The thermochromic systems of claim 1 , wherein the thermochromic system comprises a polymer.
17. The thermochromic system of claim 16 , wherein the polymer is selected from cellulose hydroxyethyl ether; cellulose carboxymethyl ether salt; hydroxy-substituted acrylates; poly(vinylacetate); poly(vinylalcohol); poly(vinyl butyral); poly(hydroxyethyl methacrylate); poly(1-glycerol methacrylate); hydroxyalkylcelluloses; urethanes; poly(2-ethyl-2-oxazoline); poly(N-vinylpyrrolidone); poly(ethylene-co-vinylalcohol); poly(vinyl methyl ether); poly(vinylbutyral-co-vinylalcohol-co-vinylacetate); polyacrylamide; poly(N,N-dimethylacrylamide); polyvinylpyridines and copolymers which involve the aforesaid polymer functionalities.