Conformational Kinetics in Chiral Poly(diphenylacetylene)s: A Dynamic P/M Memory Effect.

Area of Science:

• Polymer Chemistry
• Chiroptical Spectroscopy
• Materials Science

Background:

• Chiral polymers exhibit unique helical structures crucial for advanced applications.
• Controlling polymer helicity is challenging, often requiring external chiral stimuli.
• Poly(diphenylacetylene)s (PDPA) are known for their processability and potential for helical structures.

Purpose of the Study:

• To demonstrate dynamic helical memory in chiral dissymmetric poly(diphenylacetylene)s (PDPA).
• To investigate the ability to switch and retain P or M helical structures in a single polymer chain.
• To explore the influence of solvent polarity and pendant group conformation on polymer helicity.

Main Methods:

• Synthesis of PDPA bearing a chiral pendant group (benzamide of (L)-alanine methyl ester).
• Thermal annealing in low-polar solvents to stabilize specific pendant conformations.
• Solvent manipulation (low-polar to polar, e.g., DMSO) to induce and trap helical structures.
• Electronic Circular Dichroism (ECD) and Circularly Polarized Luminescence (CPL) spectroscopy to analyze helical states.

Main Results:

• A single chiral PDPA can achieve either P or M helical structures dynamically in response to solvent changes.
• Stabilization of an anti-conformer in the pendant group via thermal annealing dictates the initial helix.
• Kinetic trapping of helical structures is achieved by solvent exchange, demonstrating memory.
• The helical memory effect is present in both ground and excited states, confirmed by ECD and CPL.

Conclusions:

• Chiral PDPA exhibits dynamic helical memory, allowing reversible switching between P and M helices.
• The phenomenon relies on the interplay between pendant group conformation and solvent environment.
• This provides a pathway for designing polymers with controllable and switchable chiroptical properties.