The conformations of polymer chains in poly(ethylene oxide)/silica nanoparticles, PEO/SiO2, nanohybrids have been investigated through a combined approach that involves molecular dynamics (MD) simulations and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements. Systems with different polymer molecular weights, nanoparticle radii, and concentrations have been employed to investigate the effect of the confinement on polymer conformations across a variety of different conditions. Qualitatively similar behavior between experimental and simulation results is observed since in both cases an increase of gauche population for the OCCO angle is attained, in comparison to the respective of the bulk. This increase becomes larger as the degree of confinement becomes higher. More specifically, both simulations and experiments indicate a corresponding progressive increase with the degree of confinement. On the contrary, the conformations of the C–O bond (COCC angle) seem to remain unaffected by the confinement, at least in the range of degrees of confinement covered computationally. In addition, chain dimensions in the nanocomposite are found to be slightly decreased compared to bulk, especially at low temperatures. This results in a reduced effective confinement that allows the polymer matrix to accommodate larger nanoparticle fractions.
Identifying the role of multiple cooperative supramolecular interactions and the working mechanism underlying the formation of sophisticated, well-defined self-assembled architectures is definitely a challenging and formidable task in understanding the complexity in chemical systems and engineering the properties of advanced materials. The topological design of multifunctional tectons, capable of self-organizing into patterned supramolecular assemblies comprising stacked aromatic molecules, is of particular importance because it can lead to the predictable emergence of controlled functions with tailored electronic properties. Herein, we provide spectroscopic, structural, and mechanistic insights on metal-ion-mediated self-assembly of a charged, amphiphilic perylene-bisimide (PBI) dimer S into two-dimensional (2D) arrays consisting of parallel columnar PBI stacks with a precise spatial arrangement and pattern behavior, using a readily accessible design strategy. The building block (S), a centrosymmetric PBI homodimer bearing a disulfonated trans-stilbene core, was designed to concurrently feature high complexation directionality with a strong binding affinity through multiple supramolecular interactions. In solvents that efficiently solvate PBI, e.g., chloroform, the zinc ion interacts strongly through electrostatic interactions with the negatively charged core of S, and with the π cloud of the stilbene moiety (cation−π interactions) forming simple 1:1 adducts. In methanol, the findings manifest the efficient formation of well-defined aggregates with H-type excitonic coupling. A single-crystal X-ray structure reveals, despite the sterically crowded bay area of PBIs constituting S, an unprecedented pattern of 2D arrays comprising face-to-face, slipped π-stacked PBI interdimers that pack in parallel columns. This molecular arrangement explains the quenched fluorescence in solution, as well as the appearance of weak excimer-like fluorescence both in solution and crystals. The spectroscopic and structural findings converge to the conclusion that the development of aggregates in solution proceeds by a cooperative growth process driven by a collection of different supramolecular interactions, i.e., electrostatic (core of S), π–π stacking (terminal PBIs), and multiple C–H···π (bay substituents). A corresponding aggregation model fits satisfactorily the experimental data in solution and allows extracting the association constants and spectra of the equilibrated species.
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