Ferroelectricity and Phase Change Memory of Bis(tetradecylamide)-Substituted Benzene Derivatives

Interplay between intermolecular interactions including hydrogen bonding, halogen-halogen, and van der Waals interactions in molecular crystals leads to diverse phase transition behaviors and physical properties. Bis(tetradecylamide)-substituted benzene derivatives, terephthalamide (C14-TPA), isophthalamide (C14-IPA), and phthalamide (C14-PA), were examined, and the electric field-polarization curves of the former two crystals indicated ferroelectric hysteresis behavior in high-temperature solid phases. C14-XIPA derivatives where X = CH₃, Cl, Br, or I at the 5-position of the IPA molecule were synthesized, and the effects of substituent X on the molecular assembly structure and physical properties were investigated. H- and CH₃-substituted C14-IPA and C14-MeIPA formed a crystalline phase in which intermolecular amide-type N-H···O═ hydrogen-bonding interactions were dominant, whereas halogen-substituted C14-XIPAs formed a metastable glass phase upon cooling from the isotropic liquid. The formation of the glass phase is associated with energy competition between hydrogen bonding, halogen-halogen, and van der Waals interactions among the −CONH-, −X, and −C_nH_2n+1 units. The glass-crystal phase transition of C14-XIPAs (X = Cl, Br, or I) changes the refractive index under polarized optical microscopic observation, which can be utilized for phase-change memory.