Actuated Conformational Switching in a Single Crystal of a Homodithiacalix[4]arene

There are many reports discussing the conformational flexibility of calix[4]arenes in solution. On the other hand, similar studies concerning the solid state have received considerably less attention, even for the more extended and simultaneously more plastic calixarenes. Furthermore, no studies have been performed on single crystals, most likely because they are generally still perceived as unalterable and rigid, despite an increasing number of reports proving that the opposite is true. We report herein a phenomenon taking place in a single crystal of homodithiacalix[4]arene, the first member of a novel family of “homodiheteracalix[4]arenes”, with diatomic hetera bridges introduced in the macrocyclic ring, in this case disulfide. In contrast with the extensive literature on single-crystal-to-single-crystal transformations (SCSCT) taking place in metal–organic networks, the number of reports regarding SCSCT for organic solids is very limited to date and only encompasses a couple of examples. This is attributed to the fact that cooperative molecular motion is much more easily achieved for frameworks than in molecular crystals. To the best of our knowledge, reversible, solvent-induced conformational switching in a single crystal of an organic solid has not been reported to date. Moreover, the process is correlated with the formation/disappearance of channels in the structure. Jones et al. observed a change in conformation of an organic cage induced by solvent; however the single crystal did not survive this transformation, and a detailed study was performed on powdered bulk material instead. Keeping in mind that the structural changes observed in our case do not lead to loss of the crystal integrity, the transformation seems to be quite remarkable. The compound I (Scheme 1) was obtained by applying the concept of dynamic covalent chemistry (DCC), an attractive approach whereby a reversible reaction is performed under