Solid-state Porphyrin Interactions with Oppositely Charged Peripheral Groups

Area of Science:

• Supramolecular Chemistry
• Crystal Engineering
• Materials Science

Background:

• Porphyrins are versatile macrocyclic compounds with diverse applications.
• Understanding the self-assembly of charged porphyrins is crucial for designing novel materials.
• Electrostatic and pi-pi interactions play key roles in molecular recognition and self-assembly.

Purpose of the Study:

• To elucidate the crystal and molecular structure of a specific pair of oppositely charged porphyrins.
• To investigate the stabilizing interactions within the assembled porphyrin structures.
• To understand the formation of one-dimensional stacks in porphyrin assemblies.

Main Methods:

• Crystallization of the porphyrin pair: tetra-anion 5,10,15,20-tetrakis-(4-sulfonatophenyl)-21,23H-porphyrin [H2TPPSO3]4- and tetra-cation 5,10,15,20-tetra(N-methylpyridyl)21H,23H-porphyrin [H2TMePyP]4+.
• X-ray diffraction analysis to determine the crystal and molecular structure.
• Analysis of intermolecular interactions, including electrostatic and pi-pi stacking.

Main Results:

• The formation of an alternating one-dimensional stack of the tetra-anion and tetra-cation porphyrins.
• Stabilization of the stack by strong electrostatic interactions between the oppositely charged porphyrin rings.
• Additional stabilization provided by pi-pi interactions between the substituted phenyl rings of adjacent porphyrins.
• Exceptionally tight packing and interactions within the porphyrin ensemble.

Conclusions:

• The study successfully determined the crystal structure of a unique porphyrin pair.
• Electrostatic and pi-pi interactions cooperatively drive the formation of stable, one-dimensional porphyrin stacks.
• The findings provide insights into the rational design of self-assembled supramolecular structures based on porphyrins.