In the phenanthroline strapped porphyrin did not only provide a site for molecular recognition, it also provided a space for CuAAC reactions due to the presence of the phenanthroline binding site for copper (Figure 4). As a result, the use of bulky alkyne and azide stoppers led to the preparation of various rotaxanes species (X-ray structure Figure 4 right).¹

Fig. 4. Mechanism proposed for the tandem activity of zinc and copper in CuAAC (left), X-ray structure of a rotaxane containing a free-base porphyrin in the macrocycle (right).

Using this approach, a fullerene stoppered rotaxane has been prepared. Time resolved fluorescence studies performed in the group of Prof. D. Guldi in Erlangen have shown that excitation of the porphyrin induces a motion of the fullerene stoppered dumbbell and leads to long lived charge separated species in coordinating solvents. ²

1. CuAAC in a Distal Pocket: Metal Active-Template Synthesis of Strapped-Porphyrin [2]Rotaxanes Chem. Eur. J. (2017), 23,13579-13582.
2. Light triggers molecular shuttling in rotaxanes: control over proximity and charge recombination Chem. Sci. (2019), 10, 3846-3853.