Vapochromism of Ionic Dyes in Thin Films of Sugar Gels

Solid thin films of sugar gels containing ionic dyes, such as flavylium and thionine salts, exhibit extensive and vapor-specific color changes upon exposure to volatile organic compounds, such as methanol, ethanol, acetone, benzene, ether, and pyridine. Some of them show good vapochromic reversibility after repeated exposures, although extensive degradation occurs with pyridine vapor. Vapochromism has been explained in terms of solvation and stabilization of the dye molecules by permeated vapors, resulting in a shift of dye aggregation-deaggregation equilibria.