The flexibility of the bridging alkyl chains is important for proximity in the stacking of porphyrin and phthalocyanine conjugated through a fourfold rotaxane linkage. This picture shows a chochin, a Japanese lantern made with paper and thin strips of bamboo that can be expanded and contracted flexibly. This foldability recalls the induced molecular interaction in the flexible molecular conjugate. More information can be found in the Research Article by K. Tanaka et al. (DOI: 10.1002/chem.202200819).

Invited for the cover of this issue are Kentaro Tanaka at Nagoya University and co‐workers. The image depicts the importance of the flexibility of bridging alkyl chains in a molecular conjugate to pack the components closely to generate efficient molecular communication. Read the full text of the article at 10.1002/chem.202200819.

Spatial distance is an important factor in controlling the functional interactions between molecular units in a conjugate; therefore, the bridging unit has been closely examined. Here, we examined the effect of the flexibility of bridging alkyl chains on the proximity of stacked porphyrin and phthalocyanine conjugated with a fourfold rotaxane linkage. We found that closely stacking two π systems requires bridging alkyl chains above a certain length, and the shorter bridges hinder stacking because of their lower flexibility. The stacking distance between porphyrin and phthalocyanine in the conjugate with decyl (C10) chains was estimated to be 4.03 Å and showed a unique physical character arising from short‐distance interactions. The longer alkyl chains minimized steric restriction inside the fourfold rotaxane and allowed efficient communication between the porphyrin and phthalocyanine units. This is due to the flexibility of the side chains.