A Ferroelastic Salt Cocrystal with Ultraviolet Emission

The coexistence and coupling of photoluminescence and ferroelasticity in a single matter are vitally important for developing multifunctional materials and devices. However, the effective construction of ferroelastics with efficient photoluminescence, especially in the ultraviolet range, is a great challenge. In this work, a salt cocrystal, (DPA)(DPAH)PF₆ (DPA = diphenylamine, DPAH = diphenylamine cation), with ultraviolet emission and ferroelasticity was reported by introducing the anion group PF₆^– in the parent DPA crystal. Besides, the thermally triggered order–disorder transition of PF₆^– groups leads to a ferroelastic phase transition at ∼340 K with the Aizu notation of 2/mF1̅. In addition, (DPA)(DPAH)PF₆ displays a bright ultraviolet emission at 392 nm with a photoluminescence quantum yield of 49.4%. This work presents a strategy to achieve ultraviolet (UV)-emissive ferroelastic based on the luminescent organic crystal, which not only extends the luminescence of ferroelastic to the UV region but also paves a new way for the development of multifunctional ferroelastic materials and devices.