Silver nanoparticles as interactive media for the azobenzenes isomerization in aqueous solution: From linear to stretched kinetics

The thermal cis-trans isomerization of azobenzene and 4‑methoxyazobenzene has been investigated in aqueous solution in the presence of electrochemically synthesized silver nanoparticles (AgNPs) in the concentration range 0.32–32 ppm. The samples in which the investigated molecules in trans state have been converted into the cis isomer by irradiation immediately after their addition to the AgNPs solution show different kinetic behavior: in the case of azobenzene the cis-trans isomerization does not occur; in the case of 4‑methoxyazobenzene the reaction follows a first order decay. The samples in which the molecules have been added in trans state and left in solution for 120 h before their conversion into the cis isomers by irradiation show a similar behavior by which the cis-trans isomerization occurs according to the Kohlrausch-Williams-Watts stretched exponential kinetics. The UV–vis spectra and kinetics measurements performed at 25 ± 0.1 °C supported by zeta potential analysis reflect the existence of different microenvironments for the cis and trans isomers of azobenzene and 4‑methoxyazobenzene in solution in the presence of AgNPs in the investigated silver concentration range.