azobenzene

Azobenzene is an organic compound with the formula C12H10N2. It comprises two phenyl rings joined by an azo (N=N) linkage. In typical conditions it exists as two configurational isomers: the trans (E) isomer, which is more thermodynamically stable, and the cis (Z) isomer, which is less stable and can be formed by irradiation with light. The cis form gradually reverts to the trans form over time, with the rate depending on temperature and solvent.

Preparation and structure:

Azobenzene is generally prepared by azo coupling, a reaction in which a arenediazonium salt derived from an aniline couples with another activated arene to form the azo linkage. This method yields azobenzene and a variety of derivatives after purification.

Properties:

Azobenzene is a colorless to pale-yellow solid with limited water solubility but good solubility in many organic solvents. It absorbs light in the UV-visible region; the trans isomer has a characteristic absorption that decreases upon isomerization to the cis form. The two isomers have different geometries and spectral properties, making azobenzene a standard model for photoisomerization.

Applications:

Derivatives of azobenzene are widely used as dyes and as photoresponsive components in polymers, liquid crystals, and molecular devices. Its reversible light-induced switching between trans and cis forms enables optical control of properties such as shape, polarity, and intermolecular interactions, with applications in data storage, actuation, and supramolecular chemistry.