Abstract
Recent advances in the research field of supramolecularly engineered dye aggregates have enabled the design of simple one-dimensional stacks such as fibers and of closed structures such as nanotoroids (nanorings). More complex and advanced supramolecular systems could potentially be designed using a molecule that is able to provide either of these distinct nanostructures under different conditions. In this study, we introduced bulky but strongly aggregating cholesterol units to a scissor-shaped azobenzene dyad framework, which affords either nanotoroids, nanotubes, or 1D fibers, depending on the substituents. This new dyad with two trans-azobenzene arms shows supramolecular polymorphism in its temperature-controlled self-assembly, leading to not only oligomeric nanotoroids as kinetic products, but also to one-dimensional fibers as thermodynamic products. This supramolecular polymorphism can also be achieved via photo-triggered self-assembly, i.e., irradiation of a monomeric solution of the dyad with two cis-azobenzene arms using strong visible light leads to the preferential formation of nanotoroids, whereas irradiation with weak visible light leads to the predominant formation of 1D fibers. This is the first example of a successful light-induced modulation of supramolecular polymorphism to produce distinctly nanostructured aggregates under isothermal conditions.
Highlights
Recent advances in the area of molecular self-assembly have allowed creating supramolecularly engineered nanostructures from various functional molecules.[1]
atomic force microscopy (AFM) images of the PSSVis sample revealed the formation of nanotoroids as well as fibrous aggregates (Fig. 5d), which demonstrates that the supramolecular polymorphism of 1 occurs in this phototriggered self-assembly (Fig. 5e), albeit that unlike the selfassembly by rapid cooling, it does not go through a metastable state
We had controlled the self-assembly pathways of our azobenzene dyads through side-chain engineering (Fig 1a)
Summary
Recent advances in the area of molecular self-assembly have allowed creating supramolecularly engineered nanostructures from various functional molecules.[1]. A cross-sectional analysis revealed heights of 1.6, 3.1, and 4.8 nm (FigV.iew2dA)rt.icleTOhnelisnee thickness values indicate the stackinDgOI:o1f0.1t0w39o/D2tSoC00th69re0Ae nanotoroids.[11] Despite this higher-order-aggregation tendency, extended stacking of the nanotoroids to afford tubular assemblies, which was observed for the planar nanotoroids of previously reported dyads, was not observed even upon cooling the solution to 0 °C (Fig. S3a).
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