exTTF as a Building Block for Fullerene Receptors. Unexpected Solvent-Dependent Positive Homotropic Cooperativity

The first exTTF-based receptor for molecular recognition of fullerene is described. Unexpectedly, the receptor shows completely different binding modes in chlorobenzene and CHCl3/CS2 mixtures. In the aromatic solvent, the receptor binds C60 in a noncooperative fashion (n H = 1) with a K assoc = (2.98 ± 0.12) × 103 M-1, whereas in CHCl3/CS2 mixtures, it shows a marked positive homotropic cooperative effect (n H = 2.7) toward binding of C60, with an apparent binding constant of (3.56 ± 0.16) × 103 M-1. The unique solvent-switchable behavior of our receptor might find use in the controlled self-assembly of exTTF−C60 donor−acceptor ensembles.