Reversible Thermosalience as a Result of Cooperative Bond and Molecular Rotations in a Multicomponent Hydrogen-Bonded...

Thermosalient materials, which are organic or metal-organic analogs of martensitic solids, exhibit rapid mechanical responses triggered by a change in temperature. Although methods have been developed to classify thermosalient solids based on their molecular and supramolecular structures, characterizing structural changes before and after salient events is challenging due to the violent response of the crystalline material. Here, we describe a multicomponent organic solid, wherein the components self-assemble into a one-dimensional hydrogen-bonded polymer, and reversible thermosalient behavior was discovered. Thermosalient solids typically undergo overall small structural changes; surprisingly, detailed structural analysis before and after the transition demonstrates cooperative bond and molecular rotations lead to significant sliding between layers, which is preceded by anisotropic expansion of the cell. Layer sliding affords the formation of significant π-stacking interactions, and calculations show the two phases are similar in energy. This work provides direct insight into structural changes during salient events, aids in understanding stimuli-responsive molecular solids, and discusses supramolecular interactions as stabilizing yet flexible motifs that can enable dynamic structural properties.