Synthesis, properties and applications of macrocyclic azobenzenes

Azobenzenes are a versatile class of compounds, which find applications in various areas. Not only does their family make up several of the most important organic dyes and pigments, they also exhibit photochromism. The structural change from E to Z geometry, which is induced when subjected to UV-light, widens their potential applications and makes them an exciting topic especially for functional materials. Furthermore, the isomerization is completely reversible in most cases. The work of this thesis was focused on fully conjugated macrocyclic azobenzenes. Several derivatives of two different macrocycles with three azobenzene units were prepared to study their photochemical properties as well as potential applications. The first macrocycle, cyclotrisazobenzene, was first prepared by Dreiding and coworkers. After the development of an improved synthetic strategy three different derivatives of the macrocycle were prepared. Photochemical studies showed that the system was inert to photoisomerization. Binding studies on the macrocycle with alkaline metal ions as well as triphenylcarbenium ions were conducted and suggested the formation of complexes. Cyclotrisazobiphenyl as the second system was based on biphenyls which were connected by three azobenzene bonds at meta positions to form a macrocycle. After a synthetic path to these larger macrocycles was established, the properties of different derivatives were studied. For a hexa-MOM-protected derivative an extensive study of the photochemical E → Z isomerization was done. Ester derivatives of the macrocycle showed π-π-stacking interactions in solution and exhibited liquid crystalline properties. A chiral derivative of the macrocycle was also prepared which showed a change of its chiroptical properties upon irradiation and was used as a ternary switch with a CD-spectroscopic readout. To link the macrocycle to DNA templates, it was tried to link nucleobases to the macrocycle, which was not successful. By connecting two alkine functionalized cyclotrisazobiphenyls with a click reaction to an anthracene linker, an organogel was obtained in toluene which switched its gelation properties upon irradiation with UV-light.