Mutual binding of polymer end-groups by complementary π-π-stacking: a molecular "Roman Handshake"

Area of Science:

• Supramolecular Chemistry
• Polymer Science
• Organic Chemistry

Background:

• Tweezer-molecules offer precise control over molecular recognition and assembly.
• Naphthalenediimide (NDI) cores are known for their electronic properties and ability to participate in π-π stacking.
• Hydrogen bonding is a key non-covalent interaction for stabilizing molecular assemblies.

Purpose of the Study:

• To design and synthesize self-complementary tweezer-molecules based on a naphthalenediimide core.
• To investigate the self-assembly behavior of these molecules in solution.
• To explore the impact of these self-assembled structures on polymer properties.

Main Methods:

• Synthesis of naphthalenediimide-based tweezer-molecules.
• Spectroscopic analysis (e.g., NMR, UV-Vis) to confirm structure and assembly.
• Isothermal titration calorimetry (ITC) to determine binding constants.
• Size exclusion chromatography (SEC) to assess polymer molecular weight changes.

Main Results:

• Self-complementary tweezer-molecules self-assemble into stable supramolecular dimers via π-π stacking and hydrogen bonding.
• The supramolecular dimer exhibits high stability in solution with a binding affinity constant (K(a)) of 10^5 M⁻¹.
• Grafting the tweezer-dimer motif to poly(ethylene glycol) (PEG) resulted in a doubling of the polymer's apparent molecular weight.

Conclusions:

• Naphthalenediimide-based tweezer-molecules are effective building blocks for stable supramolecular dimers.
• This supramolecular dimerization strategy can significantly alter polymer characteristics.
• The findings present a new method for modifying polymer properties through controlled self-assembly.