Foldamer-Derived Preorganized Bi- and Tri-zinc Porphyrin Tweezers for a Pentafluorobenzene-bearing Pyridine Guest: The Binding Pattern Study

By introducing two and three zinc porphyrin units to one side of hydrogen bonding-induced aromatic amide foldamers, two new molecular tweezers 1 and 2 have been prepared. To explore new possible binding patterns, a leucine-based pyridine ligand 3 that bears a pentafluorophenyl group has been prepared. UV-Vis and 1H NMR experiments reveal that 1 and 2 favorably complex one or two molecules of 3. UV-Vis titration experiments show that the apparent association constants of the complexes of the zinc porphyrin units of the two receptors and 3 are considerably higher than that of the complex between a simple control zinc porphyrin and 3. In the presence of excess of 3, the left zinc porphyrin unit of 1 and 2 can bind one more molecule of 3, which is, however, stabilized only by the single Zn-N coordination.