Azobenzene molecule — Photomechanical properties and applications of molecular switching

The azobenzene or azo molecule is a molecule that allows reversible switching of its molecular system by an isomerization reaction giving two different states of the molecule with the same atoms but in a different arrangement. A remarkable difference in absorption spectra is made between the two switching states by absorption of a photon. This molecule, which changes color when illuminated, also belongs to the family of photochromic molecules. This molecular switching takes place mainly using light as a stimulus, but can also be activated at the level of the molecule alone by the electron current from the tip of a scanning tunneling microscope.

Using azobenzene's particular photocommutable characteristics, a variety of functional systems can be synthesized using different materials, from liquid crystals to polymers and biological molecules. Applications using this molecule are numerous at all dimensional scale levels, such as high-density optical data storage, molecular switches for photoactivated membranes, photocontrolled logic gates, photoelastic ribbons and surfaces, nanoparticles for photoeffaceable inks, electronic/optical systems, bio-imaging surfaces.

This article will begin with a brief description of the azobenzene molecule, leading from solution systems to functional materials and light-activated polymers. Examples of the use of this molecule will cover the fields of photonics, biology and molecular electronics.

Future developments of these photocommutable systems in practical applications, as well as existing challenges, will also be presented and put into perspective with regard to the demands of miniaturization and the evolution of nanotechnology.