Supramolecular polymerization based on the metalation of porphyrin nanosheets in aqueous media

Abstract

Despite its great potential in supramolecular chemistry to achieve structural complexity and sophisticated functionality, the kinetic control over molecular self-assembly in coordination with supramolecular polymerization still constitutes a challenge. Herein, the kinetically controlled supramolecular polymerization of porphyrin derivatives was achieved in aqueous media by a seeding method based on a metastable state generated by synergistic metalation and Lewis acid–base complexation. As a monomer, free-base porphyrin 1_free bearing four amide-linked ethylene glycol side chains was synthesized. In aqueous media, monomeric 1_free self-assembles into H-type aggregates, which then transformed into J-type aggregates in the presence of Zn(II) ions via metalation of 1_free, affording Zn–porphyrin complex 1_Zn. The distinct porphyrin cores of 1_free and 1_Zn undergo different aggregation pathways. In the presence of Zn(II) ions, the H-type aggregation formed by 1_free is in the metastable state, and the synthesis of monomeric 1_Znvia metalation retards the spontaneous J-aggregation. The seeding method was successfully applied to produce two-dimensional nanosheets in the presence of Zn(II) ions. This kinetically controlled metalation provides a platform for the development of supramolecular metal-based structures with controlled size, morphology, and chemical properties.