Switchable nanoassembly from an azobenzene-containing dye

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Amphiphilic molecules with distinct hydrophilic and hydrophobic regions can self-assemble in solution.
• Azobenzene derivatives are known for their photoresponsive properties and potential in self-assembly.
• Understanding the influence of pH on molecular self-aggregation is crucial for designing responsive materials.

Purpose of the Study:

• To investigate the optical properties and morphology of an amphiphilic azobenzene dye (1).
• To explore the pH-dependent self-aggregation behavior of dye 1.
• To characterize the formation of supramolecular structures induced by pH changes.

Main Methods:

• Synthesis and characterization of the amphiphilic azobenzene dye 1.
• Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) for morphological analysis.
• pH titration to determine the pKa and study aggregation changes.

Main Results:

• Dye 1 exhibits pH-dependent self-aggregation, forming scattered morphologies at neutral pH (7.0) and aggregated vesicular-like structures at alkaline pH (10.5).
• The hydroxyl group's pKa of 9.38 governs the deprotonation and subsequent negative charging of the nanoparticles.
• The observed aggregation is driven by hydrophobic interactions between the alkyl chains and is reversible with pH changes.

Conclusions:

• The amphiphilic azobenzene dye 1 demonstrates tunable, pH-responsive self-aggregation.
• Reversible switching between scattered and aggregated states by adjusting pH offers potential for smart materials.
• The formation of supramolecular aggregation-induced vesicular structures highlights the design principles for responsive nanomaterials.