Aqueous Supramolecular Co-Assembly of Anionic and Cationic Photoresponsive Stiff-Stilbene Amphiphiles

Fabrication of macroscopic soft functional materials, such as macroscopic photoresponsive soft materials and artificial muscles, can be commonly prepared by charge screening of supramolecular assemblies with inorganic salt solutions using a shear-flow method. However, some of the charged end-groups of photoresponsive molecular amphiphiles cannot be stabilized with inorganic salt solutions to fabricate macroscopic soft materials. Stiff stilbene amphiphiles (SAs) functionalized with anionic phosphite and cationic quaternary ammonium end groups are designed and synthesized and their photochemical and supramolecular assembly properties are determined. Supramolecular co-assembly of anionic and cationic nanotubes of SAs allows to transform into nanoribbons, confirmed by transmission electron microscopy, critical aggregation concentration, and Zeta potential measurements. Nanoribbons of anionic and cationic SAs can be prepared into macroscopic soft materials with inorganic salt solutions and surprisingly also with deionized water. The macroscopic soft material of anionic and cationic SAs can be stabilized at low concentration ≈5 mm. Meanwhile, the photoresponsiveness of the macroscopic soft materials is retained to provide macroscopic morphological change upon photoirradiation. These results exhibit the feasibility in fabrication of macroscopic functional soft materials from supramolecular assembly across multiple length-scale without help of inorganic salts and offer ample opportunity in developing future soft supramolecular robotic systems.