Small alterations to the structure of a star‐shaped template totally change its mode of
operation. The hexapyridyl template directs the conversion of a porphyrin dimer to the cyclic
hexamer, but deleting one pyridine site changes the product to the cyclic decamer, while
deleting two binding sites changes the product to the cyclic octamer. This surprising switch
in selectivity is explained by the formation of 2: 1 caterpillar track complexes, in which two
template wheels bind inside the nanoring. Caterpillar track complexes can also be prepared …

Significance: Oligo-pyridines have been used as templates to direct the synthesis of zinc-
porphyrin nanorings. The authors showed that a hexapyridyl template directed the synthesis
of a cyclic zincporphyrin hexamer, removal of one binding site on the hexapyridyl template
produced a cyclic decamer and removal of two binding sites produced a cyclic octamer. An
interesting discovery of these zinc-porphyrin nanorings is that while the nanorings are static
when they are coordinatively saturated with the binding sites on the pyridine templates …