Counter-Anion Effect on the Thermal Stability of Amorphous Solid Films of Indotricarbocyanine Dyes under Highly Humid Conditions

Abstract

In order to obtain an insight into the thermal stability of cyanine dye films for optical recording discs, deterioration rates of amorphous solid films of nine indotricarbocyanine dyes were measured at 60°C and 90% relative humidity. The dyes were made up of the combinations of 5-chloro-2-[7-(5-chloro-1, 3-dihydro-1, 3, 3-trimethyl-2H-indol-2-ylidene)-hepta-1, 3, 5-trienyl]-1, 3, 3-trimethyl-3H-indolium and nine colorless anions. Films with relatively hydrophilic anions faded faster than those with hydrophobic ones did. The order of the deterioration rates coincides with the order of hydrophilicity of the films as estimated from water-contact angles, suggesting that the surface-adsorbed water participates in the rate-determining step.