Abstract
Precise control over the ratio of perylene bisimide (PBI) monomers and aggregates, immobilized on alumina nanoparticle (NP) surfaces, is demonstrated. Towards this goal, phosphonic acid functionalized PBI derivatives (PA-PBI) are shown to self-assemble into stoichiometrically mixed monolayers featuring aliphatic, glycolic, or fluorinated phosphonic acid ligands, serving as imbedding matrix (PA-M) to afford core-shell NPs. Different but, nevertheless, defined PBI monomer/aggregate composition is achieved by either the variation in the PA-PBI to PA-M ratios, or the utilization of different PA-Ms. Various steady-state as well as time-resolved spectroscopy techniques are applied to probe the core-shell NPs with respect to changes in their optical properties upon variations in the shell composition. To this end, the ratio between monomer and excimer-like emission assists in deriving information on the self-assembled monolayer composition, local ordering, and corresponding aggregate content. With the help of X-ray reflectivity measurements, accompanied by molecular dynamics simulations, the built-up of the particle shells, in general, and the PBI aggregation behavior, in particular, are explored in depth.
Highlights
Precise control over the ratio of perylene bisimide (PBI) monomers and synthetic fibers and resins,[4] imaging dyes in bioanalysis,[5] light harvesting applicaaggregates, immobilized on alumina nanoparticle (NP) surfaces, is demonstrated
The basic NP nomenclature, that is, AlOx@X%phosphonic acid functionalized PBI derivatives (PA-PBI)/PA-M, infers that X represents the molar ratio fraction of PA-PBI and PA-M, whereby PA-M is a placeholder for PA-CH3, PA-O-CH3, or PA-CF3
To rationalize the experimental observations, we performed molecular dynamic simulations to gain atomic-scale insights into PA-PBI aggregation within self-assembled monolayers (SAMs) of different PA-Ms Considering that the NP average diameter is about 50 nm, our 5–10 nm scale simulation systems were modeled as molecular arrangements of PA-Ms and PA-PBIs on a flat surface, mimicked by an AlOx slab with periodic boundary conditions (PBC) applied in x- and y-directions
Summary
Myriads of recent and past publications have shown that the absorption and fluorescence properties of PBIs are strongly concentration-dependent.[2]. Which enables the overall stoichiometric variability in terms of the PA-PBI to PA-M ratios on the NP surfaces, which was corroborated in recent studies.[19,20,21,22] For the NP functionalization, solutions of varying molar ratios of PA-PBI and PA-CH3 were prepared, whereby the lowest PA-PBI concentration was set to 5.0 × 10−5 m These solutions were mixed with a fixed volume of AlOx dispersions (see the Supporting Information for further details). The results (see Figures S4–S11, Supporting Information) suggest a much higher thermal stability of PA-PBI when adsorbed onto the NP surface In both cases, that is, with and without the NPs, decomposition of the linker is followed by that of PBI. The overall trend correlates well with the intrinsic rigidity of PA-Ms, which has been investigated in a recent study.[20]
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