Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates Exploited as Photo-Switchable Alignment Medium

Area of Science:

• Polymer Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Photo-responsive polymers offer dynamic control over material properties.
• Azobenzene derivatives are widely used photo-switches due to their reversible E/Z isomerization.
• Polyaspartates provide a versatile scaffold for designing functional polymers.

Purpose of the Study:

• To synthesize and characterize novel polyaspartates bearing ortho-fluorinated azobenzene photo-responsive groups.
• To investigate the light-induced conformational changes (coil-helix transitions) in these polymers.
• To explore the self-assembly behavior, including liquid crystal formation, and potential applications in enantiomer differentiation.

Main Methods:

• Synthesis of polyaspartates with pendant ortho-fluorinated azobenzene groups (PpFABLA) and a co-polymer (PpFABLA-co-PBLA).
• Investigation of visible-light-induced E/Z isomerization and subsequent coil-helix transitions using spectroscopy and viscometry.
• Characterization of liquid crystalline phases (lyotropic liquid crystals) and their orientation under magnetic fields.
• Assessment of the polymers as alignment media for measuring dipolar couplings and differentiating enantiomers.

Main Results:

• PpFABLA undergoes reversible visible-light-induced coil-helix transitions (green light: coil, violet light: helix).
• The ortho-fluorinated azobenzene group enhances the thermal stability of the helical Z-isomer.
• Helical PpFABLA forms a magnetically orientable lyotropic liquid crystal (LLC) at 20% concentration.
• The co-polymer PpFABLA-co-PBLA maintains a helical structure regardless of photo-isomerization, forming an LLC at 16% concentration.
• PpFABLA serves as an alignment medium for measuring dipolar couplings and distinguishing enantiomers.

Conclusions:

• Novel photo-responsive polyaspartates with enhanced thermal stability of the helical state were successfully synthesized.
• Light-induced conformational changes drive the formation of liquid crystalline phases with tunable properties.
• These polymers demonstrate significant potential as advanced alignment media for molecular structure determination and chiral recognition.