Solvent-Driven Supramolecular Wrapping of Self-Assembled Structures

Abstract

Self-assembly relies on the ability of smaller and discrete entities to spontaneously arrange into more organized systems by means of the structure-encoded information. Herein, we show that the design of the media can play a role even more important than the chemical design. The media not only determines the self-assembly pathway at a single-component level, but in a very narrow solvent composition, a supramolecular homo-aggregate can be non-covalently wrapped by a second component that possesses a different crystal lattice. Such a process has been followed in real time by confocal microscopy thanks to the different emission colors of the aggregates formed by two isolated Pt^II complexes. This coating is reversible and controlled by the media composition. Single-crystal X-ray diffraction and molecular simulations based on coarse-grained (CG) models allowed the understanding of the properties displayed by the different aggregates. Such findings could result in a new method to construct hierarchical supramolecular structures.

Keywords: luminescence; metal-metal interactions; platinum; self-assembly; supramolecular chemistry.

Figure 1

a) Structures of compounds 1 and 2. b) Top: Molecular structure of 1 determined by single‐crystal X‐ray diffraction and aggregated structure of the compound showing the long Pt‐Pt distance. Bottom: molecular structure of 2 determined by single‐crystal X‐ray diffraction and π‐stacked structure of compound 2 showing the short Pt‐Pt distances. c) Schematic representation of the packing observed in compounds 1 (top) and 2 (bottom).

Figure 2

a) Depolymerization profile of compound 2 (c=5×10⁻⁵ M) showing the PLQY and emission maximum, as a function of the ratio water:dioxane in the system. b) Spectra profile of the depolymerization experiment for 2, from the starting orange emissive aggregates at high water content (red line spectra) to a second class of yellow‐emissive structures (yellow line) below 70 % water content, to the molecularly dissolved state when the water content is below 50 % (blue line), λ_ex=313 nm. c) Depolymerization profile of compound 1 (c=1×10⁻⁴ M) showing the PLQY and emission maximum, as a function of the % of water in the system. d) Spectra profile of the depolymerization experiment for 1, the starting orange‐emissive aggregates at high water content (red line spectra) to a the blue‐emitting nanoribbons (blue line) below 70 % water content to the molecularly dissolved state when the water content is below 30 %, λ_ex=313 nm. Spectra profile of the depolymerization experiment for 1 adapted, with permission of Springer Nature, from ref. [12]. e) Snapshots taken from Supplementary Movie 1 showing the time‐dependent evolution of the yellow assemblies (2B) by confocal microscopy at 65 % water content (λ_ex=405 nm) (more information is provided in the SI).

Figure 3

a) Top: Confocal microscopy time‐progression of the evolution of the wrapping by compound 2 on the preformed fibers of compound 1 at 60 % water content (Snapshots taken from Supplementary Movie 2). Bottom: Emission spectra (recorded under the microscope) in different parts of the fiber (arrows indicate the point of acquisition) corresponding to the times shown in the top pictures (λ_ex=405 nm). b) Snapshots taken from Supplementary Movie 3 showing the confocal microscopy time‐progression of the disassembly of 2 from fibers 1C (λ_ex=405 nm). c) Schematic representation of: (top) the coating process by 2 on fibers 1C as depicted in panels a), (medium) the scenario after the coating process and (bottom) the representation after the de‐coating experiment promoted by the change in solvent composition (panels b).

Figure 4

a) Molecular models of monomers 1 and 2: all‐atom (solid stick) and CG (superimposed transparent spheres) monomer models. b) Snapshots of the self‐assembly of 1 monomers (in blue) into fiber 1 (solvent not shown for clarity) after 2.5 μs of CG‐MD. The inset shows the initial configuration with dispersed monomers. c) Same as panel b, for the self‐assembly of 2 monomers (in yellow). d) Identification of defects in fiber 1: plot of the interaction energy ΔE ₁(i) of the individual 1 monomers with all the other monomers in fiber 1 as a function of their SASA (and ⟨SASA₁⟩ are the average values over all monomers, indicated by dashed black lines in the plot). Defects are displayed as red points. e) Copolymerization with 2 proceeds through defects: plot of the ΔE ₁(i) and SASA of the individual 1 monomers for increasing amounts of 2 monomers in the system. Different colors correspond to a different amount of 2 monomers in solution. The dashed lines indicate the average values for each series of data (1 monomers become less and less exposed to the solvent and more strongly interacting with the rest of fiber 1 when surrounded by 2 monomers). The co‐assembly data are extracted after 2.5 μs of CG‐MD. The snapshot shows the co‐assembly of 200 2 monomers (yellow) with fiber 1 (grey, defects highlighted in red) after 2.5 μs of CG‐MD.