Azobenzene Container Showing a Definite Folding – Synthesis and Structural Investigation

The combination of photo-switchable units with macrocycles is a very interesting field in supramolecular chemistry. Here, we present the synthesis of a foldable container consisting of two different types of Lissoclinum macrocyclic peptides which are connected via two azobenzene units. The container is controllable by light: Irradiation with UV light causes a switching process to the compact cis,cis isomer, whereas by the use of visible light the stretched trans,trans isomer is formed. By means of quantum chemical calculations and CD spectroscopy we could show that the trans → cis isomerization is spatially directed; that means that one of the two different macrocycles performs a definite clockwise rotation to the other, caused by irradiation with UV light. For the cis → trans isomerization counterclockwise rotations are found. Furthermore, quantum chemical calculations reveal that the energy of the cis,cis isomer is only slightly higher than the energy of the cis,trans isomer. This effect can be explained by the high dispersion energy in the compact cis,cis isomer.