Frontiers in Materials (Jan 2024)

Azo dye polyelectrolyte multilayer films reversibly re-soluble with visible light

  • Mikhail Kim,
  • Coral Hillel,
  • Kayrel Edwards,
  • Tristan H. Borchers,
  • Ozzy Mermut,
  • Ozzy Mermut,
  • Ozzy Mermut,
  • William J. Pietro,
  • Christopher J. Barrett,
  • Christopher J. Barrett

DOI
https://doi.org/10.3389/fmats.2024.1334863
Journal volume & issue
Vol. 11

Abstract

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Polymeric multilayer films were prepared using a layer-by-layer (LBL) technique on glass surfaces, by repeated and sequential dipping into dilute aqueous solutions of various combinations of water-soluble polyanions (polyacrylic acid (PAA)), polycations (polyallylamine hydrochloride (PAH) or chitosan (CS)), with bi-functional water-soluble cationic azo dyes bismark brown R bismarck brown red or bismark brown Y (BBY), or anionic azo dyes allura red (ALR) or amaranth (AMA), as ionic cross-linkers. The electrostatically-assembled ionically-paired films showed good long-term stability to dissolution, with no re-solubility in water. However, upon exposure to low power visible light under running water, the films photo-disassembled back to their water-soluble constituent components, via structural photo-isomerization of the azo ionic crosslinkers. The relative rate of the disassembly (RRD) of the films was established using UV-Vis spectroscopy, demonstrating that these assemblies can in principle represent fully recyclable, environmentally structurally degradable materials triggered by exposure to sunlight, with full recovery of starting components. A density functional theory treatment of the allura red azo dye rationalizes the geometrical isomerization mechanism of the photo-disassembly and provides insight into the energetics of the optically-induced structural changes that trigger the disassembly and recovery.

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