Abstract:

It was found that ionic liquid-like polyoxometalates(IL-POM) functionalized by sulfonic acid possess reversible photochromic properties. Detailed photochromism of [PyPS]_nH_3-nPW₁₂(n=1,3), [PyPS]₄SiW₁₂ and [TEAPS]₃PW₁₂ samples were investigated. IL-POMs functionalized by sulfonic acid are a class of salts with weak charge-transfer effect. Under UV irradiation, however, electron interaction between organic cations and POM anions results in the reduction of W⁶⁺ to W⁵⁺. The formation of a stable charge-transfer complex leads to the coloration. The photochromic ability of tungstophosphate is stronger than that of tungstosilicate. The decoloration occurred in air when the colored sample was placed in dark. But the sample is easily fatigued and a coloration-decoloration cycle with poor reproducibility is observed. A study on photochromic mechanism shows that -SO₃H group in organic cation is involved in photochromic process as an electron donor. This reveals the donor property of sulfonic acid and provides a new strategy for designing charge-transfer polyoxometalates and POM-based photochromic materials.

Key words: polyoxometalates, ionic liquid, functionalized by sulfonic acid, photochromism, mechanism