Ultra‐Fast Molecular Rotors within Porous Organic Cages

Using variable temperature (2)H static NMR spectra and (13)C spin‐lattice relaxation times (T(1)), we show that two different porous organic cages with tubular architectures are ultra‐fast molecular rotors. The central para‐phenylene rings that frame the “windows” to the cage voids display very rapid rotational rates of the order of 1.2–8×10(6) Hz at 230 K with low activation energy barriers in the 12–18 kJ mol(−1) range. These cages act as hosts to iodine guest molecules, which dramatically slows down the rotational rates of the phenylene groups (5–10×10(4) Hz at 230 K), demonstrating potential use in applications that require molecular capture and release.