The effect of dye-polymer interactions on the kinetics of the isomerization of 4-dimethyl-aminoazobenzene and mercury dithizonate

Abstract

Thermal and photo-isomerization reactions of mercury dithizonate and 4-dimethyl-aminoazobenzene were studied in solutions and in polymer matrices. We used exponential functions to calculate the rate constants for both processes. The kinetic behavior was well described by monoexponential functions for these dyes dissolved in solvents, although bi-exponential functions are required when these dyes are dissolved in polymers. The rate constants are strongly influenced by dye/solvent and dye/polymer interactions, as well as by the aging processes of the polymer matrix. In general, the reaction is faster in more polar mediums, solvents or polymer matrices, since stabilization of different tautomers takes place. We also showed that larger molecules isomerize slowly and slower isomerization has also been observed for annealed samples. Both results are attributed to the importance of free-volumes in polymeric matrices.