Solvent and viscosity effect on the kinetics of the thermal cis-trans isomerization of 3'-nitro-4-diethylaminoazobenzene

The thermal cis-trans isomerization of 3'-nitro-4-diethylaminoazobenzene in various solvents and in poly (ethyleneglycol methylethers) of different molecular weights has been studied kinetically as a function of temperature. The dependence of the experimental data on medium polarity, using both alcohols and aprotic solvents, and on polymer viscosity is discussed and compared with the behaviour of other similar dyes. An inversion mechanism, passing through an sp-hybridized linear transition state, appears to be the general path for all 4-diethylaminoazobenzenes. No viscosity effect could be observed. The possibility of using this reaction as a probe of the dynamic behaviour of bulk polymer molecules is discussed.