Decoding Elastic, Plastic, and Elastic–Plastic Deformation in Aryl Benzoate Molecular Crystals via Substituent‐Driven Interaction Hierarchies

Mechanical flexibility in molecular crystals is crucial for their integration into adaptive and flexible technologies, yet it remains challenging to predict and control. We report a systematic study of the structure-mechanical properties of 36 p-substituted aryl benzoate ester crystals. They exhibit a range of mechanical responses-elastic, plastic, elastic-plastic, and brittle. By varying the type and position of substituents, we were able to tune intermolecular interaction hierarchies, packing anisotropy, and deformation pathways. Three-point bending experiments, combined with single-crystal X-ray diffraction (SXRD), molecular electrostatic potential (MESP) analysis, Hirshfeld surface (HS) analysis, surface rugosity, attachment energy calculations, and energy-framework analysis, reveal the structural origins of distinct mechanical behaviors. Elasticity in these crystals is linked to the corrugated packing with balanced, reversible dispersive interactions; plasticity, in contrast, is driven by layered architectures with weak interlayer interfaces and accessible slip planes. Elastic-plastic transitions emerge from a subtle balance between stiff intralayer frameworks and stress-sensitive interlayer contacts. The study provides a comprehensive and predictive framework for understanding the structure-mechanical relationships in molecular crystals. It offers robust design principles for engineering organic solids with tailored elastic and plastic properties.