Shape-persistent rings and wheels

Shape-persistent macrocycles based on the arylene-ethynylene backbone are synthetically challenging targets that can be obtained in good to high yields either by statistical or by template-supported oxidative Glaser coupling of the corresponding bisacetylenes. The macrocycles can be adsorbed on highly oriented pyrolytic graphite (HOPG) to form well-ordered monolayers as visualized by scanning tunneling microscopy (STM). Moreover, bithiophene-containing macrocycles are able to bind fullerenes at the electron-rich sites of the rings. One-dimensional tubular structures based on shape-persistent macrocycles can also be obtained by oxidative acetylene coupling. These contain intraannularly bound conjugated polymers and represent bichromophoric systems that allow an accumulation of excitation energy on the conjugated core. In the field of defined 2D objects we describe molecular spoked wheels with a lateral expansion of more than 5 nm. These compounds are highly rigid. In order to provide sufficient solubility, they contain peripheral substituents and additional substituents orthogonal to the plane of the molecules.