A Cofacial Porphyrin Dimer Generated by Cooperative Zinc Ion Binding

Abstract

Noncovalent cofacial porphyrin dimers have attracted interest due to their potential use as host materials or catalysts. In this study, we introduce a novel coordination‐directed cofacial porphyrin dimer from a meso‐tetraphenylporphyrin derivative modified with 2,2'bipyridine moieties at the meta positions of the phenyl groups. Spectroscopic investigation has shed light on the binding processes and the structure of the dimer in solution in detail. Initial Zn2+ ion binding to the porphyrin hinders the subsequent Zn2+ binding and the binding of the second porphyrin. However, once the dimer is formed, additional Zn2+ binding is notably enhanced, resulting in a pronounced S‐shaped binding curve. The detailed structure of the dimer in solution was established based on UV‐vis spectroscopy, various 1H NMR spectroscopy techniques and mass spectrometry. Simulations of ringcurrent‐induced chemical shift changes provided evidence for the face‐to‐face porphyrin structure with tetrahedral coordination of the bipyridine ligands. The X‐ray single crystal structure provided conclusive evidence for the structure of the face‐to‐face dimer, which remarkably resembles the model structure from the 1H NMR simulation. The stability of the dimer structure makes it promising for further exploration of this motif in developing new supramolecular structures and for their potential applications as host compounds and catalysts.