Selective Extraction of C_(70) by a Tetragonal Prismatic Porphyrin Cage

Along with the advent of supramolecular chemistry, research on fullerene receptors based on noncovalent bonding interactions has attracted a lot of attention. Here, we present the design and synthesis of a cationic molecular cage: a cyclophane composed of two tetraphenylporphyrins, bridged face-to-face by four viologen units in a rhomboid prismatic manner. The large cavity inside the cage, as well as the favorable donor–acceptor interactions between the porphyrin panels and the fullerene guests, enables the cage to be an excellent fullerene receptor. The 1:1 host–guest complexes formed between the cage and both C_(60) and C_(70) were characterized in solution by HRMS and NMR, UV–vis and fluorescence spectroscopies, and confirmed in the solid state by single-crystal X-ray diffraction analyses. The results from solution studies reveal that the cage has a much stronger binding for C_(70) than for C_(60), resulting in a selective extraction of C_(70) from a C_(60)-enriched fullerene mixture (C_(60)/C_(70) = 10/1), demonstrating the potential of the cage as an attractive receptor for fullerene separation