Novel Aspects Regarding the Photochemistry of Azo-Derivatives Substituted with Strong Acceptor Groups

Abstract

In this paper, an extended isomerization study of a series of nitro/cyano mono- and disubstituted azo-monomers and related azo-poly­(methacrylate)­s is conducted by UV–vis and 1H NMR spectroscopy. The experiments, carried out in both toluene and dimethylformamide (DMF), reveal an intriguing behavior. The monosubstituted azo-derivatives, thermally relax monotonously via inversion mechanism, in both solvents. Interestingly, the disubstituted azo-derivatives reveal stable Z isomers in DMF, while in toluene they exhibit very fast relaxation, by inversion. The particular stability of Z isomers in DMF is explained in terms of solvent–solute interactions, using quantum chemical calculations and Fourier transform-infrared spectroscopy. In addition, the information–transmission capability with time of one disubstituted azo-monomer is highlighted. The study reveals that the nature and position of substituents on the azo-moiety, and as well as their interaction with the solvent, have a crucial importance for the Z–E thermal relaxation and for the displayed photochromic properties.

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

“…In addition, we were not able to calculate the k i value of C4S derivative in toluene, due to the very fast thermal back relaxation. Our group reported for the first time similar behavior on related disubstituted azobenzene structures [25]. In our earlier report the azo-derivatives where substituted on one phenyl ring with cyano and/or nitro and with methacrylate groups on the other phenyl ring.…”

“…For monosubstituted azobenzenes, the percentage of Z isomer produced upon irradiation is higher in toluene, while for the disubstituted azo-derivatives is much higher in DMF. This atypical behavior can be explained by the stabilization of Z isomer through dipole-dipole interaction with DMF, as demonstrated by our group in a recent published paper [25].…”

“…Interestingly, the disubstituted azobenzenes do not thermally relax back to the E state in DMF. This peculiar behavior was first noticed for similar azo-derivatives with related chemical structures [25], whereas the same electron withdrawing groups and the same substitution pattern was preserved, but with different electron donating group (methacrylate). Therefore, we may safely conclude, that this unusual stability of Z isomer derives from the substitution pattern with the strong acceptor groups and their interactions with the solvent, and not by the strength of the electron donating groups placed on the other phenyl ring.…”

“…The azobenzene-type molecules can isomerize from Z configuration back into E configuration very slow when bulky substituents are introduced to hinder the thermal relaxation [23,24]. Moreover, recent studies conducted by our group revealed that it is even possible to yield stable Z-isomers, when a proper solvent is used [25]. In addition, the nature and position of substituents on the aromatic rings had a great contribution to this behavior.…”

Epoxy‐Based Azopolymers with Enhanced Photoresponsive Properties Obtained by Cationic Homopolymerization

“…In the past few decades, polymers containing azobenzene units, commonly named azopolymers, have been extensively investigated for their unique photoresponsive properties related to photoinduced trans–cis–trans isomerization of the azo chromophores . Due to these properties, azopolymers can be used for several applications in the fields of data storage, optical sensors, photonic devices, and photoprocessing among others …”