An Organic–Inorganic Hybrid Ferroelastic Semiconductor with Thermochromic Effect

Ferroelastics have attracted considerable attention due to their promising applications in energy conversion, sensing, and shape memory devices. The integration of ferroelasticity with additional physical properties, such as thermochromism and semiconductivity, in a single material offers new opportunities for advanced applications, yet significant challenges. Here, we report a bismuth-based organic–inorganic hybrid ferroelastic semiconductor, [HPym] 3 [H 2 Pym][Bi 2 Br 11 ] (Pym = pyrimidine), which exhibits a narrow band gap of 1.62 eV. It undergoes a reversible ferroelastic phase transition with Aizu notation of 4/ m F2/ m at 282 K. More importantly, the phase transition is accompanied by a reversible thermochromic behavior, characterized by a color change from red to yellow. The coexistence of ferroelasticity, thermochromism, and semiconductivity in [HPym] 3 [H 2 Pym][Bi 2 Br 11 ] highlights its potential for practical applications.