Photofading Kinetics and Thermodynamics of Some Azo Disperse Dyes in Amide Solvents under the Influence of Far Ultra–violet Radiation

The paper reports some kinetic measurements of photofading of some 4′-substituted 4–diethylaminoazobenzenes in formamide, N–methy/formamide, N, N–dimethy/formamide, N–methylacetamide and N, N–dimethyiacetamide. The observed Hammett p–values suggest a reductive pathway, as confirmed by the presence of anilines among the fading products. The free energies of solvation of the dyes in the various solvents have also been calculated by measuring the distribution coefficients of the dye between the amide solvent and n–hexane, as immiscible standard solvent. A fair linear correlation exists between the observed rate constants and the free energies of transfer, suggesting the possibility that photofading rate increases with increasing solvation of dye.