Scissor-Shaped Photochromic Dyads: Hierarchical Self-Assembly and Photoresponsive Property

Unique relationships between hierarchically organized biological nanostructures and functions have motivated chemists to construct sophisticated artificial nanostructured systems from small and simple synthetic molecules through self-assembly. As one of such sophisticated systems, we have investigated scissor-shaped photochromic dyads that can hierarchically self-assemble into discrete nanostructures showing photoresponsive properties. We synthesized various azobenzene dyads and found that these dyads adopt intramolecularly folded conformation like a closed scissor, and then self-assemble into toroidal nanostructures by generating curvature. The toroids further organize into nanotubes and further into helical supramolecular fibers depending on the nature of alkyl substituents. All of these nanostructures can be dissociated and reorganized through the photoisomerization of azobenzene units. On the other hand, the introduction of stilbene chromophores instead of azobenzenes leads to one-dimensional supramolecular polymerization, which upon the intramolecular photocyclization of stilbene chromophores shifts to curved self-assembly leading to helicoidal fibers with distinct supramolecular chirality.

Hierarchical self-assembly of zwitterionic dendrimer-anionic surfactant complexes into multiple stimuli-responsive dynamic nanotubes

Zwitterionic materials attract a wide range of attention due to their unique molecular structures and properties, which make them an interesting candidate to solve multiple problems e.g. in biological and industrial applications. Here, we show that the incorporation of zwitterions into supramolecular assemblies of ionic building blocks can be an effective way to design responsive nanostructures with well-defined morphologies. We report the hierarchical assembly of stimuli-responsive nanotubes with tunable diameters in aqueous solutions via the selective attachment of anionic surfactants to dendrimers with uniquely engineered zwitterionic peripheries. We found that the packing number of the dendrimer-surfactant hybrids can be reversibly controlled, which will trigger their assembly into tubular-like structures. These tubes can grow up to the micro-scale, their diameter is responsive to the ionic strength of the solution, and they can reversibly assemble/disassemble with a change in pH. To the best of our knowledge, this is the first example of dynamic nanotubes formed through controlled ionic interactions involving zwitterionic dendrimers in solution. This not only provides a bottom-up method to make stimuli responsive and dynamic tubes but also introduce a pathway to design complicated nanostructures by controlling the electrostatic interactions of building blocks using zwitterionic functionalities.

Supramolecular Helical Nanofibers Formed by Achiral Monomers and Their Reversible Sol-Gel Transition

Well-defined supramolecular helical nanofibers have been constructed by a rationally designed achiral monomer in aqueous solution based on the 1:2 host-guest combination between cucurbit[8]uril and a 4,4'-bipyridin-1-ium chloride (BPY⁺ ) salt derivative. The formed nanostructures could be adjusted by varying the concentration of monomer from helical nanofibers to a pH-responsive hydrogel.

4-Perfluoroalkylbutoxybenzene derivatives as liquid crystalline organogelators based on phase-selective gelators

4-Perfluoroalkylbutoxybenzene derivatives as a smart soft material show efficient and rapid phase-selective gelation ability from water at extremes of pH.