Structural Origin of Crystallographic Face-Dependent Elastoplastic and Plastic Bending in an Organic Molecular Crystal.

Crystalline materials that exhibit attractive mechanical responses under external stresses have attracted considerable interest due to their potential applications across multiple fields. Here, we present a crystalline form of 9-fluorenone hydrazone (9-FH) that exhibits dual mechanical stress response, that is, plasticity and elastoplastic behavior, on different crystallographic faces. This dual mechanical response arises from specific molecular packing features, wherein intermolecular interactions play a key role in modulating the crystal's mechanical properties from the different faces. Here, large 9-FH single crystals demonstrate excellent plastic behavior under applied forces, attributed to the reorganization of weak interactions across the slip planes. Moreover, this comprehensive analysis offers detailed insights into the distinct mechanical responses of 9-FH and the underlying mechanism.