Understanding of the Kinetic Stability of cis- Isomer of Azobenzenes through Kinetic and Computational Studies

A library of halogen-substituted azobenzenes (ABs) have been synthesized and structurally characterized by single crystal X-ray diffraction technique. Azobenzenes studied herein display fast photo switching properties. Kinetics of cis- -> trans- isomerization has been studied using UV-VIS spectroscopy and the rate constant for this transformation were determined. Optimization of probable conformers of the cis- isomer and the corresponding transition state (TS) were carried out to determine the energy of activation. The Time-Dependent Density Functional Theory (TD-DFT) calculations were also performed to gain insight into the photo-isomerization. Our results indicate that the fluorinated compounds display better kinetic stability of the cis- isomer compared to the corresponding chloro and bromo analogues.