Shape Persistent Macrocycles
The term shape-persistent macrocycle means that the building blocks of the ring are rather rigid and their connection is performed in such a way that the final structure cannot collapse. More precisely, shape-persistent macrocycles have an interior (lumen) d that is, on average, equal to the contour length l of their molecular backbone divided by π:
All our structures are based on the phenylene-ethynylene backbone with m- and p substituted aromatics connected by acetylene or diacetylene units. The possibility to synthetically address the ring interior and exterior independently allows the construction of highly complex structures with a convergent and divergent functional group arrangement if these groups are located the corner pieces of the ring (m-substituted aromatics). Additionally, shape-persistent macrocycles with an adaptable arrangement can be also built if the side groups are located at the adaptable units (p-substituted aromatics).
An experimental proof for the adaptable nature of para-phenylene moieties in shape-persistent phenylene-ethynylene macrocycles was given by the single-crystal X-ray analysis of the amphiphilic macrocycle 1a (Scheme 1). Depending on the polarity of the solvent from which the crystals were grown, different conformational states could be observed.