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 1 H 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.