Large Thermo- and Mechanosalient Actuation via Cooperative Twist Elasticity-Induced Packing Motif Conversion.

Dynamic molecular crystals capable of undergoing cooperative structural transformations offer exciting prospects for next-generation actuators, sensors, and stimuli-responsive materials. However, realizing large-scale deformation in the solid state─particularly through torsional mechanisms─remains rare. Here, we examine a cyanostilbene derivative, αDDDCS, that exhibits solid-state twist elasticity enabled by cooperative conformational torsion and packing motif conversion. This system features three enantiotropic polymorphs that interconvert through thermoelastic and mechanosalient phase transitions, reflecting a competition between thermodynamic stability and kinetic accessibility, including a Y → C thermoelastic transformation involving a 27% lattice elongation─among the largest reported to date. Single-crystal X-ray diffraction, variable-temperature characterization, and quantum chemical calculations reveal that the transformation proceeds through a π-stacking-to-μ-herringbone transition, governed by a distinct torsional barrier and polymorph-specific free energy landscape. Remarkably, this is the first demonstration of twist elasticity accessed via mechanosalient actuation. Our findings establish conformational twist as a viable molecular design element for achieving high-strain responsiveness in dynamic crystals.