Clawlike tripodal porphyrin trimer: ion-controlled on–off fullerene binding

A practical method for the preparation of novel tripodal tris(porphyrinato-urea) TP3 1 was readily achieved. Because of its appreciable preorganized triangular cone-shaped cavity resulting from the intramolecular hydrogen bonds of the tripodal tris-urea backbone, this porphyrin trimer host was found to have a high affinity toward fullerenes to form stable inclusion complexes in solution. A 120-fold binding selectivity toward C70 (Kassoc = 1.81 × 10(7) M(–1)) over C60 (Kassoc = 1.51 × 10(5) M(–1)) was further achieved in toluene. Moreover, the dissociation of such inclusion complexes can be easily realized by introducing H2PO4(–), and recapturing of the fullerene can be achieved after withdrawing H2PO4(–) by Ca(2+). A recyclable process for the inclusion and release of fullerene was therefore built by alternately feeding H2PO4(–) and Ca(2+). Benefiting from this approach, TP3 1 was sequentially applied to isolate C70 from the C60-enriched fullerene mixture successfully.