Molecular Compasses And Gyroscopes: Engineering Molecular Crystals With Fast Internal Rotation

Crystals of 1,4-bis[3,3,3-tri(3,4-ditertbutyl)phenylpropynyl] benzene 1c may be viewed as a collection of molecular gyroscopes having a central p-diethynylphenylene as a rotary element encased by two bulky triarylmethyl groups. Single-crystal X-ray analysis, C-13 CPMAS NMR, and H-2 NMR quadrupolar-echo line-shape analysis revealed a lattice of molecules with phenylene groups experiencing rotary motion in the gigahertz regime near ambient temperature.