Coordination-induced cofacial dimer formation of a phenanthroline-tethered porphyrin

A zinc porphyrin bearing 4 1,10-phenanthroline units, ZnPor(phen)₄, forms cofacial dimers upon coordination with Zn²⁺ or Cu⁺ ions. Ultraviolet visible spectroscopy, electrospray ionization mass spectrometry, and ¹ H nuclear magnetic resonance ring-current analysis reveal dimers comprising 2 porphyrins linked by 4 tetrahedral M(phen)₂ complexes (M = Zn²⁺, Cu⁺). Compared with a bipyridine analog, the phenanthroline derivative exhibits higher stability, demonstrating that ligand rigidity and stronger metal–ligand binding enhance the robustness of coordination-induced porphyrin assemblies.