Dynamic Molecular Invasion into Multiply Interlocked Catenane Composed of Porphyrin and Phthalocyanine

Abstract

Commonly, in molecular inclusion phenomena or molecular recognition processes, flexibility on the molecular size or shape of a host molecule is incompatible with a high affinity of association and accuracy of selectivity. However, if the host has a narrow access for incorporating the guest, the transition process during the complexation requires a higher activation energy. A molecular elevator, which is a molecular machine composed of two planar molecular components joined with more than two interlock linkages, could solve the dilemma through dynamic molecular invasion of a guest molecule into the cage surrounded by the planar components. The movable component with macrocyclic rings fused with a planar core can migrate between two competitive recognition sites along the linear threads attached on the other planar component. However, although the macrocyclic rings are attracted to one of the recognition sites, the planar core with the rings still has the ability to move along the threads. This is because the affinity between the ring and recognition point does not help to anchor the ring at this position, but only increases the probability of the position. Therefore, this flexibility of the interlock linkage satisfies the requirement of the dynamic invasion of a guest molecule. The molecular system permits the invasion of a large guest molecule by expanding the access and stabilizing the host–guest interaction by induced fit based on the interactions between the ring and recognition point. A multiply interlocked catenane with a novel molecular topology was synthesized; a phthalocyanine bearing four peripheral crown ethers was quadruply interlocked with a cofacial porphyrin dimer bridged with four alkylammonium chains (Figure). The supramolecular conjugate has two nanospaces surrounded by a porphyrin, a phthalocyanine, and four alkyl chains to accommodate guest molecules. Because the phthalocyanine is movable along the alkyl chains, it acts as an adjustable wall, permitting the invasion of large molecules to the nanospaces without spoiling the affinity of the association. The dynamic molecular invasion allowed the intercalation of dianionic porphyrins into both the nanospaces with a high affinity. Figure 1