A Ferroelastic\nSalt Cocrystal with Ultraviolet Emission

The coexistence and coupling of photoluminescence and\nferroelasticity\nin a single matter are vitally important for developing multifunctional\nmaterials and devices. However, the effective construction of ferroelastics\nwith efficient photoluminescence, especially in the ultraviolet range,\nis a great challenge. In this work, a salt cocrystal, (DPA)(DPAH)PF<sub>6</sub> (DPA = diphenylamine, DPAH = diphenylamine cation), with\nultraviolet emission and ferroelasticity was reported by introducing\nthe anion group PF<sub>6</sub><sup>–</sup> in the parent DPA\ncrystal. Besides, the thermally triggered order–disorder transition\nof PF<sub>6</sub><sup>–</sup> groups leads to a ferroelastic\nphase transition at ∼340 K with the Aizu notation of 2/<i>mF</i>1̅. In addition, (DPA)(DPAH)PF<sub>6</sub> displays\na bright ultraviolet emission at 392 nm with a photoluminescence quantum\nyield of 49.4%. This work presents a strategy to achieve ultraviolet\n(UV)-emissive ferroelastic based on the luminescent organic crystal,\nwhich not only extends the luminescence of ferroelastic to the UV\nregion but also paves a new way for the development of multifunctional\nferroelastic materials and devices.