Crystals as Rockets: Modulation of the Salient Temperature in Cocrystals by Solvent Mixture Composition.

Harnessing mechanical motion in molecular crystals is a critical goal for developing novel energy conversion materials. Among known strategies, the ejection of guest molecules from the lattice via the jumping-mate approach offers a direct means of propulsion. Here, we present isostructural cocrystals of indolo[3,2-a]carbazole (ICZ) and (E)-1,2-di(pyridin-4-yl)ethene (BPE) that incorporate solvents such as acetone, ethyl acetate, or tetrahydrofuran. X-ray diffraction and solid-state nuclear magnetic resonance (NMR) studies confirmed the presence of solvents or solvent mixtures. Upon heating, these channel-type cocrystals exhibit a thermosalient effect, with temperature regulation achieved by releasing pure or solvent mixtures. Differential scanning calorimetry and thermogravimetry (DSC-TGA) analyses revealed that the transition temperatures changed progressively, demonstrating controllable thermal actuation through the release of occluded solvents. This work demonstrates a simple yet powerful way to regulate mechanical responses in molecular crystals, thereby advancing the design of responsive energy conversion materials.