Ultra-Fast Molecular Rotors within Porous Organic Cages

Using variable temperature H-2 static NMR spectra and C-13 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 1.2-8x10(6)Hz at 230K with low activation energy barriers in the 12-18kJmol(-1) range. These cages act as hosts to iodine guest molecules, which dramatically slows down the rotational rates of the phenylene groups (5-10x10(4)Hz at 230K), demonstrating potential use in applications that require molecular capture and release.