Cationic Azobenzenes as Light-Responsive Crosslinkers for Alginate-Based Supramolecular Hydrogels

Area of Science:

• Materials Science
• Polymer Chemistry
• Photochemistry

Background:

• Azobenzene photoswitches are key for light-driven control of intelligent materials.
• Enhancing azobenzene reactivity and water solubility is crucial for hydrogel crosslinking applications.

Purpose of the Study:

• To design and synthesize novel cationic, water-soluble azobenzenes.
• To incorporate these azobenzenes into sodium alginate to create photoresponsive supramolecular hydrogels (SMHGs).
• To investigate the photoresponsive properties and gel-sol transition behavior of these SMHGs.

Main Methods:

• Synthesis of three cationic azobenzenes (AZOs A, B, C).
• Incorporation of azobenzenes into sodium alginate (SA) to form SMHGs.
• Characterization of azobenzene photoisomerization using UV-Vis and 1H NMR spectroscopy.
• Determination of minimum gelation concentration (MGC) and evaluation of UV-light-induced gel-sol transitions.

Main Results:

• Azobenzenes exhibited efficient and rapid trans-to-cis isomerization upon UV irradiation (365 nm).
• The SMHGs demonstrated reversible gel-sol transitions triggered by UV light.
• Low concentrations of azobenzenes were sufficient to induce gelation in 5 wt% SA.

Conclusions:

• Developed water-soluble, cationic azobenzenes with fast photoresponsive properties.
• Successfully created photoresponsive supramolecular hydrogels with reversible sol-gel transitions.
• These findings offer insights for developing advanced photoresponsive materials for light-controlled applications.