Novel progresses in synthesis strategies of aromatic azo derivatives

Aromatic azo derivatives possess a particular character that is the light driven reversible isomerization between their cis- and trans-forms, which makes them excellent candidates to modulate the relative movement of different moieties. They are widely used not only in the traditional chemical industry, but also in many newly rising areas of science, such as photochemical molecular switch, super-molecular chemistry of host-guest recognition, self-assembly liquid crystal material, analysis of biomedical imaging and chemical, light driven molecular motor, and so on. The development of chromophores with characteristics, like high chemical stability, thermal stability over a wide temperature range and having two forms easily detectable by a method that does not cause irreversible molecular alterations, is a major challenge for researchers who focus their interest in this area. With the increasing need for investigating unknown aromatic azo derivatives, many novel efficient synthesis strategies are recently innovated and developed in succession. This critical review covers the various synthetic methods of aromatic azo derivatives reported more recently, with special emphasis on application of arylhydrazine, arylamine, nitroarene, azoxyarene, arylazide, and their derivatives.