Advances in understanding the photoresponsive behavior of azobenzenes substituted with strong electron withdrawing groups

• Stable Z isomers using chromophore solvent interactions were obtained.
• The kinetic parameters describing E–Z–E isomerization of azo-derivatives were calculated.
• Thermal relaxation was tuned from substitution pattern and solvent polarity.

In this paper, a detailed isomerization study of a series of 2,4-nitro/cyan substituted azobenzenes is conducted by UV–Vis spectroscopy. The experiments, carried out in both toluene and N, N′-dimethylformamide, reveal an intriguing behavior. Interestingly, the disubstituted azo-derivatives display stable Z isomers in DMF, while in toluene they exhibit very fast relaxation. In addition, the azo-derivatives thermally isomerize from the metastable Z form to the thermodynamically stable E isomer through either inversion route or rotational mechanism, depending on the chemical nature of the substituents and on the solvent polarity.

Figure optionsDownload high-quality image (120 K)Download as PowerPoint slide