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

Abstract

Solute−solvent interactions play a critical role in multiple fields, including biology, materials science, and (physical) organic, polymer, and supramolecular chemistry. Within the growing field of supramolecular polymer science, these interactions have been recognized as an important driving force for (entropically driven) intermolecular association, particularly in aqueous media. However, to date, solute−solvent effects remain poorly understood in the context of complex self-assembly energy landscapes and pathway complexity. Herein, we unravel the role of solute−solvent interactions in controlling chain conformation effects, allowing energy landscape modulation and pathway selection in aqueous supramolecular polymerization. To this end, we have designed a series of oligo(phenylene ethynylene) (OPE)based bolaamphiphilic Pt(II) complexes OPE2−4 bearing solubilizing triethylene glycol (TEG) chains of equal length on both molecule ends, but a different size of the hydrophobic aromatic scaffold. Strikingly, detailed self-assembly studies in aqueous media disclose a different tendency of the TEG chains to fold back and enwrap the hydrophobic molecular component depending on both the size of the core and the volume fraction of the co-solvent (THF). The relatively small hydrophobic component of OPE2 can be readily shielded by the TEG chains, leading to only one aggregation pathway. In contrast, the decreased capability of the TEG chains to effectively shield larger hydrophobic cores (OPE3 and OPE4) enables different types of solvent quality-dependent conformations (extended, partly back-folded and back-folded), which in turn induce various controllable aggregation pathways with distinct morphologies and mechanisms. Our results shed light on previously underappreciated solvent-dependent chain conformation effects and their role in governing pathway complexity in aqueous media.

Controlling Molecular Packing in Aqueous Metallosupramolecular Self-assembly by Ligand Geometry

“…Addition of 80/20 (v/v) THF- d 8 /D 2 O causes a weak downfield shift of all of the aromatic signals (H b , H c , H d , H e , and H f ), due to the proximity of an electron-rich group (such as the oxygen from the TEG chains) to the aromatic surface. This can occur by partial back-folding of the TEG side chains at low D 2 O content, a phenomenon that has been recently reported by our group for amphiphilic linear Pt­(II) complexes . However, the signal corresponding to the alpha bipyridine proton H a represents the only exception, showing no chemical shift variations at this stage.…”

“…hydrogen bonding) and less directional (i.e. hydrophobic interactions and π–π stacking) inter- and/or intramolecular interactions is key to control the overall self-assembly outcomes of small molecules in solution. − In this regard, molecular design strategies have been successfully exploited to control self-assembly processes, with special focus on organic compounds. − More recently, introduction of metal ions in the molecular structure of supramolecular building blocks has further boasted the supramolecular polymer field and broadened the scope of application . The incorporation of metal ions not only enriches the systems with unique redox, optical, electronic, and magnetic properties, but also provides additional intermolecular interaction sites (i.e.…”

“…Therefore, a parallel in-depth understanding (i.e. stabilization of the MMLCT state) in aqueous media is particularly relevant considering the uniqueness of water as a medium to drive biological processes. − However, achieving this goal is challenging, mainly because of the difficulty in controlling noncovalent interactions in aqueous media, which oftentimes results in unpredictable self-assembly outcomes. ,− Therefore, developing rational design strategies is a fundamental requirement to control self-assembly processes and functional properties in aqueous media. − This is typically achieved by balancing the hydrophilic/hydrophobic ratio of amphiphilic monomers; however, design approaches based on changes in the molecular geometry remain scarce.…”

Controlled Noncovalent Synthesis of Secondary Supramolecular Polymers

“…Programmable supramolecular polymerization from functional monomers offers a highly promising strategy for the synthesis of functional and adaptive soft materials. 1 By employing elegant monomer designs and implementing temperature modulation, 2 solvent mixing protocols, 3 incorporation of additives, 4 and stimuli-responsive approaches, 5 precise control over supramolecular polymerization with well-defined mechanisms has been achieved. Living supramolecular polymerization strategies 6 via kinetically delaying the nucleation process via pathway complexity 5a,7 or dormant monomers 8 have provided primary structural control, including length, dispersity, 6−8 and sequence 9 in supramolecular polymers.…”

Platinum(ii) terpyridine-based supramolecular polymer gels with induced chirality

“…11,17,18 Fernández et al investigated the molecular design and pathway complexity in supramolecular polymerization using bispyridyldichlorido Pt( ii ) complexes. 19,20…”