Photodynamic Control of the Chain Length in Supramolecular Polymers: Switching an Intercalator into a Chain Capper

Area of Science:

• Supramolecular chemistry
• Polymer science
• Materials science

Background:

• Supramolecular systems offer dynamic properties but require precise control over copolymerization.
• Controlling polymer length, composition, sequence, and morphology is crucial for advanced applications.

Purpose of the Study:

• To design photoresponsive monomers for controlled supramolecular copolymerization.
• To achieve dynamic control over polymer chain length and morphology using light stimuli.

Main Methods:

• Synthesis of photoresponsive mono acyl hydrazone functionalized benzene-1,3,5-tricarboxamide (m-BTA) monomers.
• Coassembly of m-BTA with achiral alkyl BTAs (a-BTA).
• Optical spectroscopy, light-scattering experiments, and theoretical modeling.

Main Results:

• Chiral m-BTA monomers dictate helix chirality in E isomer form and act as chain cappers in Z isomer form.
• Photoisomerization of m-BTA reversibly decreases polymer chain length in supramolecular aggregates.
• A mass-balance thermodynamic model accurately predicted copolymer composition and length distributions.
• A gel-to-sol phase transformation was observed due to light-induced chain shortening, despite the inert nature of most of the organogel.

Conclusions:

• Stimuli-responsive comonomers can amplify effects in inert polymer systems.
• Photocontrol of polymer length is achievable through dynamic chain shortening.
• This approach offers a method for macroscopic phase transformations in supramolecular materials.