Supramolecular Rotor Assemblies Exhibiting Thermally Driven Shear‐Dominated Transformation and Birefringence Switching

Abstract Multifunctional materials that combine mechanical and optical response are essential for device miniaturization and functional integration in the next‐generation smart technologies. However, achieving synergistic control over shape transformation and optical switching remains a significant challenge. Herein, two organic‐inorganic hybrid crystals exhibiting thermally induced phase transitions accompanied by pronounced shear strain and birefringence modulation are reported. At room temperature, these materials exhibit distinct birefringence, while upon heating, they adopt a high‐symmetry Fm 3— m space group, displaying optical isotropy. The structural deformation is governed by a cooperative mechanism involving a flexible supramolecular rotor [K(15‐crown‐5) ₂ ] ⁺ and inorganic InX ₄ ⁻ (X = Cl, Br) tetrahedra. Substitution of halide ions tunes the thermomechanical and optical responses: the Br–based crystal exhibits a shear strain angle of ≈10 ^° and a sharp birefringence transition from 0.0432 to optically off. These findings demonstrate a highly tunable thermo‐mechano‐optical coupling and offer a design paradigm for multifunctional responsive materials.