KINETIC-STUDY OF THE PHOTOINDUCED THERMAL CIS-TRANS-ISOMERIZATION OF AZO DYES IN HOMOGENEOUS AND MICROHETEROGENEOUS FLUID MEDIA

After flash photolysis of the stable trans isomers the rate constants of the thermal cis-trans isomerization of different ''push-pull'' 4,4' -nitro-aminoazobenzenes in homogeneous and microdisperse fluid media h ave been determined. By comparison of k(iso) with the maximum of the s olvatochromic absorption band of the pi pi charge transfer transition of the trans isomers in homogeneous solvents qualitative correlations between the isomerization rate and the solvent properties such as pol arity, viscosity and hydrogen bonding could be derived. By means of th ese results changes of k(iso) and lambda(max) with the concentration o f nonionic surfactants in water solutions and bicontinuous microemulsi ons have been interpreted.