Dielectric Response of 1,1-Difluorosumanene Caused by an In-Plane Motion

We have designed and synthesized a new curved π-conjugated molecule, 1,1-difluorosumanene (1), which possesses two fluorine atoms on the same benzylic carbon of unsubstituted sumanene, producing a large dipole moment along the in-plane direction. Thermal analyses, variable-temperature X-ray diffraction, and IR measurements indicated a 120° in-plane motion of 1 in the stacking columns, which did not cause any phase transition in the crystalline state. Indeed, dielectric measurements on powder and single-crystal forms of 1 showed that both the real (ε1) and imaginary (ε2) parts of the dielectric constant were enhanced above ~360 K at 1 MHz with a Debye-type dielectric relaxation, confirming that 1 underwent a pendulum fluctuation induced by the external electric field.