Interwoven Molecular Chains Obtained by Ionic Self-Assembly of Two Iron(III) Porphyrins with Opposite and Mismatched Charges

We report ionic self-assembly of positively charged FeIII meso-tetra(N-methyl-4-pyridyl) porphyrin (FeIIINMePyP) with negatively charged FeIII meso-tetra(4-sulfonatophenyl) porphyrin (FeIIITPPS4), leading to the formation of flower-like nanostructures composed of unprecedented three-dimensional (3D) entangled chains of porphyrin dimers. Molecular dynamics (MD) simulations show that the 3D entanglement of porphyrin chains closely correlates to mismatched charges present in porphyrin dimers like [FeIII(H2O)2NMePyP]5+/[FeIII(H2O)2TPPS4]3– that requires extra interactions or entanglement with neighboring ones to achieve electric neutrality. Interestingly, the interwoven chains bring in excellent thermal stability as evidenced by well maintenance of the flower-like morphology after pyrolysis at 775 °C in argon, which is in good agreement of high-temperature MD simulations. Meanwhile, heat treatment of the flower-like porphyrin nanostructure leads to the formation of a non-noble metal electrocatalyst (NNME) with largely inherited morphology. This exemplifies a new approach by combining ionic self-assembly with subsequent pyrolysis for the synthesis of NNMEs with desired control over the morphology of template-free NNMEs that has rarely been achieved prior to this study. Furthermore, our electrocatalyst exhibits excellent activity and durability toward oxygen reduction reaction as well as much better methanol tolerance compared with commercial Pt/C in alkaline solutions.