Photofading of Azo Pyridone Dyes in Solution

Abstract

We report on the investigation and kinetic measurements of the photofading process of some o-, p-substituted azo pyridone dyes in formamide, N,N-dimethylformamide, and N,N'-dimethylacetamide. The free energies of solvation of dyes in the three solvents have been calculated by measuring the distribution coefficients of the dyes between the amide solvent and n-hexane as the immiscible standard solvent. A fair linear correlation exists between the observed rate constant and the free energies of transfer, suggesting the possibility that the photofading rate increases with increasing solvation of dyes; moreover it is increased by two electron-withdrawing substituents.