FaFrit

Just as mechanical force applied to the strings of a violin produces beautiful sounds, mechanical stress acting on polymers leads to interesting chemical reactions. In their Communication on page 3040 ff., W. Weng et al. show that when mechanically loaded, a spirothiopyran-containing polymer turns bright green and undergoes cross-linking. Two distinct chemical responses to a mechanical load are combined in a single reactive site.

Macromolecular [2]rotaxanes comprising a polymer axle and crown ether wheel were synthesized to evaluate the effect of component mobility on the properties of the axle polymer, especially its crystallinity. Living ring-opening polymerization of δ-valerolactone with a pseudorotaxane initiator with a hydroxy group at the axle terminus was followed by end-capping with a bulky isocyanate. This yielded macromolecular [2]rotaxanes (M2Rs) possessing polyester axles of varying molecular weights. The crystallinity of the axle polymers of two series of M2Rs, with either fixed and movable components, was evaluated by differential scanning calorimetry. The results revealed that the effect of component mobility was significant in the fixed and movable M2Rs with a certain axle length, thus suggesting that the properties of the axle polymer depend on the mobility of the polyrotaxane components.

Stop and go: Macromolecular [2]rotaxanes, consisting of a polyester axle and crown ether wheel, were synthesized with either fixed or movable components and with various molecular weights to evaluate the effect of component mobility on the axle polymer properties. Crystallinity measurements revealed that the effect of mobility is significant, thus suggesting that the properties of the axle polymer depend on the mobility of the polyrotaxane components.

A synthetic strategy for the generation of new molecular species utilizing a provision of nature is presented. Nano-dimensional (23(2)×21(1)×16(1) ų) hetero-four-layered trimetallacyclophanes were constructed by proof-of-concept experiments that utilize a suitable combination of π⋅⋅⋅π interactions between the central aromatic rings, tailor-made short/long spacer tridentate donors, and the combined helicity. The behavior of the unprecedented four-layered metallacyclophane system offers a landmark in the development of new molecular systems.

Hetero-four-layered tripalladium(II) cyclophanes have been prepared. The synthesis of this series of new compounds was accomplished by a combination of effective transannular π⋅⋅⋅π interactions, tailor-made short/long tridentate ligands, and Lewis basicity of donating groups.