Dual-Channel Control of Ferroelasticity in a Soft Molecular Crystal Induced by Perfluorinated Substitution

Molecular ferroelastic materials have been widely studied because of their superior physical properties including lightweight, good biocompatibility, structural tunability, and low acoustic impedance. However, the discovery of molecular ferroelastic materials with desirable mechanical properties seems like looking for a needle in a haystack due to the lack of effective theories to control and optimize ferroelasticity. In this work, we successfully constructed the molecular ferroelastic material amantadine–pentafluorobenzoic acid (AM-PFBA) based on the chemical design strategy of perfluorinated substitution. AM-PFBA undergoes a ferroelastic phase transition with the Aizu notation of 2/mF1¯$\overline{\mathrm{1}}$$\overline{\mathrm{1}}$ at 354 K. The stripe-shaped ferroelastic domains can be reoriented under temperature or stress. Notably, AM-PFBA shows good mechanical flexibility with a small elastic modulus (E) of 6.45 GPa and hardness (H) of 0.32 GPa, which is much smaller than that of most organic crystals. Such a unique mechanical property of AM-PFBA crystal may be attributed to the introduction of fluorine atoms. This work offers an efficient strategy for precisely designing high-performance molecular ferroelastic.