An 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 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 -isomer, whereas by the use of visible light the stretched -isomer is formed. By means of quantum chemical calculations and CD spectroscopy we could show that the → 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 → isomerization counterclockwise rotations are found. Furthermore, quantum chemical calculations reveal that the energy of the isomer is only slightly higher than the energy of the -isomer. This effect can be explained by the high dispersion energy in the compact -isomer.