Azobenzene can be used as an optical trigger for the design and synthesis of a large variety of photoresponsive systems. In Vitro: Photochromic compounds that undergo large conformational changes when exposed to light of appropriate wavelength are particularly attractive as molecular switch elements. Azobenzene is a popular choice among the chromophores. The thermodynamically favored trans isomer is rapidly converted to the cis isomer by irradiation at the wavelength of the π-π* transition, whereas the reverse process is achieved either (slowly) by thermal relaxation in the dark or (quickly) by irradiation at the wavelength of the n-π* transition. The azobenzene amino acid (aa) can be used as a photo-inducible conformational switch in polypeptides. A reversible conformational change of the peptide backbone is induced by switching between the cis and trans configurations of the azobenzene moiety by irradiation with light of suitable wavelength^[1]. Azobenzene has been the most widely used optical trigger for the synthesis of photoresponsive systems ranging from poly-a-amino acids to innovative materials with light-controlled mechanical and optical properties. Its use in form of appropriate derivatives allow to generate cyclic peptide structures of constraint conformational space and thus to exploit its reversible photoisomerization to induce well defined transitions between different conformational states^[2]. Azobenzene photoswitches can be used to drive functional changes in peptides, proteins, nucleic acids, lipids, and carbohydrates^[3].