Ferroelectricity and Phase Change Memory of Bis(tetradecylamide)-Substituted Benzene Derivatives
Ryohei Mizoue, Moeko Kawana, Takashi Takeda, Norihisa Hoshino, Tomoyuki Akutagawa
Abstract
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 = CH 3, 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 CH 3 -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 n H 2 n +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.