Chemistry of Macrocage Molecules with a Bridged π-Electron System as Crystalline Molecular Gyrotops

Abstract

Rotation of the part of the molecules has been of interest in terms of artificial molecular rotors, which are one of the classes of molecular machines. We have been investigated macrocage molecules with a bridged π-electron system have been synthesized as “crystalline molecular gyrotops”, because the interior π-electron system can be rotate even in a crystal. These molecules were easily synthesized by applying silicon junctions that connect the π-electron rotor and three alkyl spokes. In this paper, chemistry of molecular gyrotops having phenylene, biphenylene, naphthalene-diyl, thiophene-diyl, and thiophenedioxide-diyl rotors have been described. Their cage structures were successfully confirmed by X-ray crystallography. Rotation of the rotor was investigated by solution and solid-state NMR spectroscopy. Some of them showed crystal-to-crystal phase transitions between static and dynamic states of the rotor, and their mechanisms were discussed.