Flexible organic ferroelastic crystals solution pH engineering

Abstract

Ferroelastic crystals possess the intrinsic ability to undergo reversible switching of spontaneous strain under external mechanical stimuli, holding tremendous potential for sensing, data storage, and flexible wearable electronics. Owing to their exceptional flexibility and biocompatibility, pure organic ferroelastics have become attractive candidate materials for ferroelastic applications. However, the fabrication of organic ferroelastics via the strategy of pH-regulated protonation remains unreported to date. Herein, we tune the protonation degree of DABCO through pH adjustment, successfully synthesizing monoprotonated DABCO-TFMS·H2O (DABCO = triethylenediamine, TFMS = trifluoromethanesulfonate) and diprotonated DABCO-(TFMS)2. The former undergoes low-temperature phase transitions without ferroelastic behaviour, while the latter exhibits a pronounced 4/mmmFmmm-type ferroelastic phase transition at 403 K, with reversible rearrangement of ferroelastic domains upon application of external mechanical stress. This work expands the ferroelastic material library, demonstrates that pH-regulated protonation is a robust strategy for achieving controllable phase transitions, and opens a new research paradigm for the development of next-generation flexible electronics and switchable devices.