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Abstrct Constructing and regulating the cyanine dye aggregates have been constantly pursued because of their wide applications in photosensitizers, biological fluorescence probes, nonlinear optics, etc. However, to realize such a process using a single additive still remains a formidable challenge. Here, the aggregation and disassembly of positively charged 3,3-diethyloxadicarbocyanine iodide (DiOC2(5)) have been demonstrated just by changing the concentration of an artificial poly(phenylenediethynylene)-based helical foldamer (Poly-1) bearing L-alanine sodium pendants with an amide linker. Poly-1 possessed the negatively charged pendants and hydrophobic helical grooves. Upon simple mixing of equal DiOC2(5) and Poly-1, DiOC2(5) molecules were mainly enriched on Poly-1 surface driven by electrostatic interaction and arranged along the main chain of Poly-1, resulting in the formation of chiral H-aggregates. But, the excessive Poly-1 would attract some DiOC2(5) molecules in H-aggregates via electrostatic interaction. The isolated monomers were easy to orderly disperse into the helical grooves due to hydrophobic interaction. Meanwhile, during the aggregation and disassembly, the solution color changed from peachblow to purple red and then to purple and finally to navy blue.

Supramolecular hydrogels have been widely investigated, but the construction of stimuli-responsive mono-component host-guest hydrogels remains a challenge in that it is still hard to balance the solubility and gelation ability of the gelator. In this work, three azobenzene-modified β-cyclodextrin derivatives with different alkyl lengths (β-CD-Azo-Cn) have been synthesized. The length of the alkyl chain dramatically influences the solubility and gelation ability of β-CD derivatives in water. Among these derivatives, β-CD-Azo-C8 possesses the lowest minimum gelation concentration (MGC). Based on the host-guest interaction between β-CD and azobenzene units in aqueous solution, which is confirmed by UV-visible and ROESY NMR spectra, the gelators self-assemble and further interwine into networks through the hydrogen bonds on the surface of β-CD cavities. Hydrogels formed by mono-component gelators can collapse under external stimuli such as heating, competition guests and hosts, and UV irradiation. When the concentration of the gelator is more than 8 wt%, the hydrogel exhibits good self-supporting ability with a storage modulus higher than 104 Pa. The gel-sol transition temperature of the hydrogel is near body temperature, indicating its potential applications in biological materials.

Photoresponsive supramolecular gels with various applications are being constantly pursued; however, achieving well-defined morphology changes of gels via light irradiation remains a formidable challenge. In this study, a gel is prepared through halogen bond between azopyridine-containing Azopy-C10 and 1,4-tetrafluorodiiodobenzene. The gel exhibits gel-sol transition due to trans-cis isomerization of the azopyridine moiety upon UV irradiation. During this transition, the morphologies vary from flake to fluffy bobble-like and finally to peony-like with increasing exposure time, which is difficult to achieve in traditional assembly systems. The microstructure change is attributed to the variations of cis-isomer content and halogen-bonding strength. The supramolecular gel provides a novel method to achieve photomodulated morphologies and broadens the applications of such kind of materials, ranging from information storage to high-tech anticounterfeit.