Confined Spaces in [n]Cyclo-2,7-pyrenylenes

A set of strained aromatic macrocycles based on [n]cyclo-2,7-(4,5,9,10-tetrahydro)pyrenylenes is presented with size-dependent photophysical properties. The K-region of pyrene was functionalized with ethylene glycol groups to decorate the outer rim and thereby confine the space inside the macrocycle. This confined space is especially pronounced for n=5, which leads to an internal binding of up to 8.0×10⁴ m^-1 between the ether-decorated [5]cyclo-2,7-pyrenylene and shape-complementary crown ether-cation complexes. Both the ether-decorated [n]cyclo-pyrenylenes as well as one of their host-guest complexes have been structurally characterized by single-crystal X-ray analysis. In combination with computational methods the structural and thermodynamic reasons for the exceptionally strong binding have been elucidated. The presented rim confinement strategy makes cycloparaphenylenes an attractive supramolecular host family with a favorable, size-independent read-out signature and binding capabilities extending beyond fullerene guests.