The Kinetics of the Cis-to-Trans Thermal Isomerization of 4-Anilino-4’- Nitroazobenzene are Highly Influenced by Solvent Polarity

Thermally‐Induced Reactions of Aromatic Crystalline Nitroso Compounds

“…High negative activation entropies (about ‐170 J K −1 mol ‐1 ) were explained by the torsional rotation around the N=N bond. Similar trends were found also for other substituted aromatic azo‐compounds . In contrary, high positive entropies for the observed Z ‐ E isomerization of 1 and 2 (Table ) resemble to the values found for the irreversible dissociations of azodioxide ( vide supra ).…”

Structural Chemistry-Assisted Strategy toward Fast Cis–Trans Photo/Thermal Isomerization Switch of Novel Azo-Naphthalene-Based Polyimides

“…According to literature data, the predominant mechanism involves the rotation around the azo bond, with the breaking of π bonds under π–π* excitation. , The outstanding fast response under irradiation clearly evidenced that the intermolecular interactions between the azo chromophore and solvent molecules controlled the isomerization process rate of these PIs and the corresponding diamines by virtue of an advantageous molecular design. The development of intermolecular hydrogen bonds between the nitrogen atom of the azo group and the solvent molecules favors the fast switch to cis species, which appears to be the key to the obtained fast isomerization kinetics. , On the other hand, the solvent polarity increase can better assist the rotation mechanism toward fast switch, which is also true for these PIs according to the UV–vis absorption data obtained for solvents with various polarities reported in the previous section. In this context, the values of the photoisomerization constant rate ( R ) should be considered.…”

“…Thus, photoisomerization rate constant values of 5.22 × 10 –2 , 8.6 × 10 –2 , 8.4 × 10 –2 , and 2.94 × 10 –2 were obtained for M1 , P1 , P2, and P3 , respectively. Because of the non-assisted substituent effect on the isomerization process, the present PIs display fast photoisomerization response to 365 nm UV light irradiation in DMF solutions and can compete even with small molecules containing an azo chromophore . The different photoisomerization kinetics among the PIs can be rationalized in terms of dipole-type interactions between the solvent molecules and polymer chains, with P3 having the most important contribution because of the presence of fluorine atoms.…”

Self-aggregation, H-bonding, and photoresponse in film and solution states of azobenzene containing polyurea

“…S3 for the orbital nature, ESI †) shifts to a longer wavelength, [61][62][63] resulting in the overlap of the two bands at 400 nm. The polarity of solvent may affect the NQN bond length, as well as the energy of electronic transitions of the NQN bond 64,65 (also see Table 2).…”