Chirality-controlled spontaneous twisting of crystals due to thermal topochemical reaction

Significance Recently many crystals have been reported to show various mechanical responses when triggered by stimuli (heat, light, and pressure). Such properties are attributed to polymorphic transitions, conformational changes, packing changes, isomerizations, or chemical reactions inside the crystal and the consequent strain developed between parent and daughter phases. The role of molecular chirality in such macroscopic phenomena is yet to be established. In the present study we found that crystals of dipeptide LL undergo right-handed twisting and those of its enantiomer, dipeptide DD, undergo left-handed twisting upon heat-induced topochemical azide–alkyne cycloaddition. This study provides clear evidence for the role of molecular chirality in controlling the direction of macroscopic twisting of crystals.