Three Distinct Polar Phases, Isotropic, Nematic, and Smectic-A Phases, Formed from a Fluoro-Substituted Dimeric Molecule with Large Dipole Moment

A dimeric molecule, di-5(3FM-C4T), with fluoro-substitutedmesogeniccores composed of three-aromatic rings and linked by a pentamethylenespacer is prepared. Di-5(3FM-C4T) forms the ferroelectric nematic(N-F), ferroelectric smectic-A (SmAP(F)), and polarisotropic (Iso(P)) phases. The N-F phase is composedof molecules in U-shaped conformation that behave like polar rod-likemolecules. The reversal spontaneous polarization (P (s)) is approximately 8 & mu;C cm(-2),which is extremely large and reflects the huge dipole moment (11.2D) of the one-side mesogenic core. On the other hand, the SmAP(F) phase is formed by bent-shaped molecules. The N-F-SmAP(F) phase transition thus follows the conformationalchange of molecules. The reversal P (s) ofthe SmAP(F) phase is around 4 & mu;C cm(-2), which is half of that in the N-F phase, and this is anexpected value from the bent shape of the molecules. It is interestingthat the highest temperature Iso(P) phase still exhibitsthe polar structure and possibly retains some polar aggregation ofmolecules in small domains. The three polar phases exhibit the dielectricmode due to the collective polarization fluctuation at around 100Hz, giving the high dielectric constant over 8000.

Automated summary

A dimeric molecule di-5(3FM-C4T) with fluoro-substituted mesogenic cores forms three different phases: ferroelectric nematic (N-F), ferroelectric smectic-A (SmAP(F)), and polarisotropic (Iso(P)). The N-F phase consists of U-shaped molecules behaving like polar rod-like molecules, while the SmAP(F) phase is formed by bent-shaped molecules. The highest temperature Iso(P) phase retains a polar structure and possibly some polar aggregation of molecules. All three polar phases exhibit a dielectric mode at around 100 Hz, resulting in a high dielectric constant of over 8000.