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/mF1̅ 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.