Porphyrin tripod as a monomeric building block for guest-induced reversible supramolecular polymerisation

Abstract

Reversible supramolecular polymerisation and depolymerisation of biomacromolecules are common and fundamental phenomena in biological systems, which can be controlled by the selective modification of biomacromolecules through molecular recognition. Herein, a porphyrin tripod (DPZnT) connected through a triazole bridge was prepared as a monomeric building block for guest-induced supramolecular polymerisation. Although the lone pair electrons in triazolic nitrogen potentially bind to the zinc porphyrin units through axial ligation, the intrinsic steric hindrance suppressed the coordination of the triazole bridge to the porphyrin unit in DPZnT. Therefore, DPZnT formed spherical nanoparticles through π-π interactions. The addition of 1,3,5-tris(pyridine-4-yl)benzene (Py3B) caused the guest-induced fibrous supramolecular polymerisation of DPZnT by forming a 1:1 host-guest complex, which was further assembled into a fibrous polymer. Furthermore, addition of Cl− to DPZnT induced the transformation of spherical nanoparticles to fibrous supramolecular polymers. The fibrous supramolecular polymers of DPZnT obtained by adding Py3B or Cl− were depolymerised to their original spherical particles after adding Cu(ClO4)2 or AgNO3, respectively.