Cycloparaphenylenes (CPPs) are hoop-shaped π-conjugated molecules in which paraphenylene units are linked in a cyclic manner. They represent the simplest structural unit of armchair carbon nanotubes.

Shigeru Yamago, Kyoto University, Japan, and colleagues, recently reported the first example of a host–guest complex of CPP and C₆₀. Such host–guest complexes are suitable models for elucidating convex–concave π–π interactions.

Now they treated a mixture of CPPs with C₆₀. [10]CPP selectively encapsulated C₆₀ forming the shortest fullerene-peapod (see picture). Such complementary host–guest complexes could be useful for the size- and shapeselective separation of higher fullerenes and carbon nanotubes.

• Size-Selective Encapsulation of C₆₀ by [10]Cycloparaphenylene: Formation of the Shortest Fullerene-Peapod,
  Takahiro Iwamoto, YoshikiWatanabe, Tatsuya Sadahiro, Takeharu Haino, Shigeru Yamago,
  Angew. Chem. Int. Ed. 2011, 50.
  DOI: 10.1002/anie.201102302