Hierarchical porphyrin self-assembly in aqueous solution

Area of Science:

• Supramolecular Chemistry
• Materials Science

Background:

• Meso-tetrakis(4-phosphonatophenyl)porphyrin exhibits self-aggregation in aqueous media.
• This aggregation follows the "sergeant-soldier rule," indicating a specific directional growth mechanism.

Purpose of the Study:

• To investigate the self-aggregation behavior of meso-tetrakis(4-phosphonatophenyl)porphyrin in aqueous solution.
• To explore how partial protonation of phosphonic groups influences aggregation pathways and resulting properties.

Main Methods:

• Aqueous solution studies of meso-tetrakis(4-phosphonatophenyl)porphyrin.
• Controlled partial protonation of external phosphonic groups.
• Monitoring of aggregation processes and characterization of resulting species.

Main Results:

• Partial protonation of external phosphonic groups directs the self-aggregation process.
• Two distinct pathways emerge: (i) further protonation of inner nitrogen atoms or (ii) time-dependent aggregation.
• These divergent pathways yield species with differing chemico-physical properties.

Conclusions:

• The "sergeant-soldier rule" governs porphyrin self-assembly.
• Protonation state critically controls the evolution and properties of porphyrin aggregates.
• Tailoring protonation offers a method to control supramolecular structure and function.