Molecular Gyrotops with a Five-Membered Heteroaromatic Ring: Synthesis, Temperature-Dependent Orientation of Dipolar Rotors inside the Crystal, and its Birefringence Change

Abstract

Three-dimensional arrays of dipolar rotors were constructed as single crystals of molecular gyrotops, which are macrocage molecules with a bridged dipolar rotor. In this study, we synthesized novel molecular gyrotops with a five-membered heteroring, i.e., furan-diyl (1), thiophene-diyl (2), and selenophene-diyl (3), and investigated the temperature-dependent orientation and rotation of the dipolar rotors inside the crystal. Unfortunately, furan derivative 1 did not crystallize; however, crystal structures of the other molecular gyrotops, i.e., 2 and 3, showed three-dimensional arrays of dipolar rotors. Thermal order–disorder transitions of the dipolar rotor orientation inside the crystal were observed in 2 and 3 with the transition temperature in selenophene derivative 3 being lower than that of thiophene derivative 2. This may be ascribed to subtle differences in the molecular structure, e.g., the intersection angle between two Si–C(aryl) bonds corresponding to the rotation axis. In accordance with the t...