Dual-Channel\nControl of Ferroelasticity in a Soft\nMolecular Crystal Induced by Perfluorinated Substitution

Molecular ferroelastic materials have been widely studied\nbecause\nof their superior physical properties including lightweight, good\nbiocompatibility, structural tunability, and low acoustic impedance.\nHowever, the discovery of molecular ferroelastic materials with desirable\nmechanical properties seems like looking for a needle in a haystack\ndue to the lack of effective theories to control and optimize ferroelasticity.\nIn this work, we successfully constructed the molecular ferroelastic\nmaterial amantadine–pentafluorobenzoic acid (AM-PFBA) based\non the chemical design strategy of perfluorinated substitution. AM-PFBA\nundergoes a ferroelastic phase transition with the Aizu notation of\n2/<i>m</i>F1̅ at 354 K. The stripe-shaped ferroelastic\ndomains can be reoriented under temperature or stress. Notably, AM-PFBA\nshows good mechanical flexibility with a small elastic modulus (<i>E</i>) of 6.45 GPa and hardness (<i>H</i>) of 0.32\nGPa, which is much smaller than that of most organic crystals. Such\na unique mechanical property of AM-PFBA crystal may be attributed\nto the introduction of fluorine atoms. This work offers an efficient\nstrategy for precisely designing high-performance molecular ferroelastic.