Pathway-Controlled Aqueous Supramolecular Polymerization via Solvent-Dependent Chain Conformation Effects

Area of Science:

• Supramolecular Polymer Chemistry
• Materials Science
• Physical Organic Chemistry

Background:

• Solute-solvent interactions are crucial for intermolecular association in supramolecular polymer science, especially in aqueous environments.
• Understanding these interactions is key to deciphering complex self-assembly energy landscapes and pathway selection.
• Current knowledge on solute-solvent effects in controlling self-assembly pathways remains limited.

Purpose of the Study:

• To investigate the role of solute-solvent interactions in modulating chain conformation and self-assembly pathways.
• To explore how molecular design, specifically hydrophobic core size, influences these interactions in aqueous supramolecular polymerization.
• To elucidate the mechanisms behind solvent-dependent conformational changes and their impact on aggregation pathways.

Main Methods:

• Design and synthesis of oligo(phenylene ethynylene) (OPE)-based bolaamphiphilic Pt(II) complexes (OPE2-4) with varying hydrophobic core sizes and identical triethylene glycol (TEG) chains.
• Detailed self-assembly studies in aqueous media with varying co-solvent (THF) fractions.
• Analysis of chain conformation (extended, back-folded) and aggregation pathways through experimental studies.

Main Results:

• The tendency of TEG chains to enwrap the hydrophobic core is dependent on the core size and co-solvent volume fraction.
• A smaller hydrophobic core (OPE2) leads to a single, predictable aggregation pathway due to efficient shielding by TEG chains.
• Larger hydrophobic cores (OPE3, OPE4) exhibit varied conformations (extended, partly back-folded, back-folded) enabling multiple, controllable aggregation pathways with distinct morphologies.

Conclusions:

• Solvent-dependent chain conformation effects are critical and previously underappreciated factors in aqueous supramolecular polymerization.
• Molecular design, particularly the balance between hydrophobic and hydrophilic components, allows for the modulation of energy landscapes and selection of self-assembly pathways.
• This work provides fundamental insights into controlling complex self-assembly processes in solution through solute-solvent interactions.