Mechanically interlocked carbon nanostructures represent a relatively unexplored frontier in carbon nanoscience due to the difficulty in preparing these unusual topological materials. Here we illustrate an active template method in which the key mechanical bond forming step is accomplished by leveraging unique ligand motifs to catalyze a cross-coupling reaction within the pore of a macrocycle. Once the mechanical bond has been formed, these macrocyclic ligands can then be converted into pi-conjugated structures in a subsequent synthetic step. This method provides a general strategy by which a variety of mechanically interlocked carbon nanostructures can be prepared which will enable structure-property relationships to be established for this emerging class of nanomaterials.

<p>A novel fluorescent probe design based on the interlocking of a reactive thread in a rigid nanohoop fluorophore is reported. This rotaxane design leads to size-selective sensing of thiolates in organic solution. More broadly, the work suggests the promise of mechanical interlocking to enhance the selectivity of reaction-based probes.</p>

Rings of porphyrins mimic natural lightharvesting chlorophyll arrays and offer insights into electronic delocalization, providing a motivation for creating larger nanorings with closely spaced porphyrin units. Here, we demonstrate the first synthesis of a macrocycle consisting entirely of 5,15-linked porphyrins. This porphyrin octadecamer was constructed using a covalent six-armed template, made by cobalt-catalyzed cyclotrimerization of an H-shaped tolan with porphyrin trimer ends. The porphyrins around the circumference of the nanoring were linked together by intramolecular oxidative meso-meso coupling and partial β-β fusion, to give a nanoring consisting of six edge-fused zinc(II) porphyrin dimer units and six un-fused nickel(II) porphyrins. STM imaging on a gold surface confirms the size and shape of the spoked 18-porphyrin nanoring (calculated diameter: 4.7 nm).

<p>The synthesis of nanohoop rotaxanes via two different active template strategies is reported. By preparing triazole-embedded rotaxanes, the observation of metal binding events in both organic and aqueous conditions are readily observed via dramatic changes in nanohoop emission. Inspired by this result, we then describe the design and synthesis of a new type of "self-destructing" nanohoop rotaxane that, in the presence of an analyte, releases a quenched nanohoop macrocycle resulting in a bright fluorescence response. More broadly, this work highlights the conceptual advantages of combining compact π-rich macrocyclic frameworks with mechanical bonds formed via active-template syntheses. </p><p></p>

V-shaped porphyrin dimers, with masked para-phenylene bridges, undergo efficient oxidative coupling to form meso-meso linked cyclic porphyrin oligomers. Reductive aromatization unmasks the para-phenylenes, increasing the strain. Oxidation then fuses the porphyrin dimers, providing a nanoring with curved walls. The strain in this macrocycle bends the para-phenylene and fused porphyrin dimer units (radii of curvature: 11.4 Å and 19.0 Å, respectively), but it does not significantly alter the electronic structure of the fused porphyrins.