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

Abstract

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 selfassemble 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 onedimensional supramolecular polymerization, which upon the intramolecular photocyclization of stilbene chromophores shifts to curved self-assembly leading to helicoidal fibers with distinct supramolecular chirality.

Biasing the Hierarchy Motifs of Nanotoroids: from 1D Nanotubes to 2D Porous Networks

“…Since at these experimental conditions, azobenzene dyads (S)-2 and 2 are in am olecularly dissolved state,these shifts imply the formation of the intramolecularly H-bonded pseudocycle. [21] Self-assembly of (S)-2 and 2 in non-polar solvent was studied by using VT-UV/Vis experiments.A sp reviously described for azobenzene-based supramolecular polymers, [15,22] the face-to-face stacking is inferred from variable temperature VT-UV/Vis spectra in MCH as solvent and at c T = 300 mM, unravelling ar ed-shift of the p-p*t ransition of the trans-azobenzene moieties from l max = 352 to 342 nm upon cooling (Figure 2a and S4a). Plotting the degree of…”

Biasing the Hierarchy Motifs of Nanotoroids: from 1D Nanotubes to 2D Porous Networks

“…Since at these experimental conditions, azobenzene dyads (S)-2 and 2 are in am olecularly dissolved state,these shifts imply the formation of the intramolecularly H-bonded pseudocycle. [21] Self-assembly of (S)-2 and 2 in non-polar solvent was studied by using VT-UV/Vis experiments.A sp reviously described for azobenzene-based supramolecular polymers, [15,22] the face-to-face stacking is inferred from variable temperature VT-UV/Vis spectra in MCH as solvent and at c T = 300 mM, unravelling ar ed-shift of the p-p*t ransition of the trans-azobenzene moieties from l max = 352 to 342 nm upon cooling (Figure 2a and S4a). Plotting the degree of aggregation (a), estimated from the variation of the absorbance at l = 342 nm, as af unction of temperature results in non-sigmoidal curves,w hich enables discarding an isodesmic mechanism for the supramolecular polymerization of both dyads.…”

“…[13] To attain this goal, more specific rules that establish the relation between molecular design, supramolecular structure and organization of these self-assembled entities are required. [14][15][16] In this context, we have previously reported the selfassembling features of scissor-shaped azobenzene dyad (S)-1, [15] endowed with hydrophobic side chains,which is capable of experiencing self-assembly at different levels of hierarchy (Figure 1a). In methylcyclohexane (MCH) at 20 8 8C, this scissor-shaped dyad self-assembles into homogenous toroidal nanostructures (nanotoroids).…”

Multiple Azoarenes Based Systems – Photoswitching, Supramolecular Chemistry and Application Prospects

“…Scissor shaped azobenzene dyads such as A‐57 a – c and A‐58 a – c have been synthesized, which self‐assemble in discrete nanotoroid structures, and further organize into 2D porous nanotubes (Figure 10). [44a–c] The UV irradiation in these systems causes photoisomerization and disassembly into monomers, whereas the reverse isomerization with visible light reconstructs the nanostructure assembly. Such hierarchical self‐assembly and UV‐induced disassembly change with slight modification in substituents [44a] .…”