Multiscale Modeling of Molecular Structure and Optical Properties of Complex Supramolecular Aggregates

<div> <div> <div> <p>Supramolecular aggregates of synthetic dye molecules offer great perspectives to prepare biomimetic functional materials for light-harvesting and energy transport. The design is complicated by the fact that structure-property relationships are hard to establish, because the molecular packing results from a delicate balance of interactions and the excitonic properties that dictate the optics and excited state dynamics, in turn sensitively depend on this packing. Here we show how an iterative multiscale approach combining molecular dynamics and quantum mechanical exciton modeling can be used to obtain accurate insight into the packing of thousands of cyanine dye molecules in a complex double-walled tubular aggregate in close interaction with its solvent environment. Our approach allows us not only to answer open questions on the structure of these prototypical aggregates, but also about their molecular-scale structural and energetic heterogeneity, and the microscopic origin of their photophysical properties. This opens the route to accurate predictions of energy transport and other functional properties.<br></p> </div> </div> </div>

Multiscale Modeling of Molecular Structure and Optical Properties of Complex Supramolecular Aggregates

<div> <div> <div> <p>Supramolecular aggregates of synthetic dye molecules offer great perspectives to prepare biomimetic functional materials for light-harvesting and energy transport. The design is complicated by the fact that structure-property relationships are hard to establish, because the molecular packing results from a delicate balance of interactions and the excitonic properties that dictate the optics and excited state dynamics, in turn sensitively depend on this packing. Here we show how an iterative multiscale approach combining molecular dynamics and quantum mechanical exciton modeling can be used to obtain accurate insight into the packing of thousands of cyanine dye molecules in a complex double-walled tubular aggregate in close interaction with its solvent environment. Our approach allows us not only to answer open questions on the structure of these prototypical aggregates, but also about their molecular-scale structural and energetic heterogeneity, and the microscopic origin of their photophysical properties. This opens the route to accurate predictions of energy transport and other functional properties.<br></p> </div> </div> </div>

A cut-off criterion for calculating more reliable adsorption energy distributions from gas adsorption isotherms

Adsorption energy distributions from experimental gas adsorption isotherms are capable to characterize the energetic heterogeneity of a solid surface. Unfortunately, they can only be computed by the adsorption integral equation, which represents an ill-posed problem, i.e., the solution is highly sensitive to errors in the input data. Ill-posed problems are usually solved by means of regularization, but general regularization schemata do not provide useful criteria to estimate the approximation quality. In this paper, a former presented solution strategy tailor-made for the Langmuir kernel of the adsorption integral equation is extended to Fourier transform. This yields a simple and effective cut-off criterion for the Fourier cosine transform of the adsorption energy distribution. The cut-off criterion is applied to calculate adsorption energy distributions from synthetic and experimental adsorption isotherms.

Kinetic and Equilibrium Study of the Adsorption of CO2 in Ultramicropores of Resorcinol-Formaldehyde Aerogels Obtained in Acidic and Basic Medium

In this work, aerogels were prepared using resorcinol-formaldehyde as a precursor in two synthetic routes, one basic and one acidic, to perform the adsorption of CO2 at 0 °C and atmospheric pressure. Aerogels were Characterization by N2 and CO2 Physisorption, Raman Spectroscopy, Scanning Electron Microscopy, and Infrared Spectroscopy. In general, was found that aerogels have a polymeric, disordered, three-dimensional structure and have a microporous surface. Langmuir, Freundlich, Sips and Toth equilibrium models present a good data fit of CO2 adsorption at relative pressure ranging between 1 × 10−4 and 3 × 10−2. The diffusion intra-particle kinetic model explains the setps of this process; the Elovich model also showed a good fit, therefore, there are an energetic heterogeneity of the CO2 superficial adsorption sites. The aerogel carbonized in basic medium at 1050 °C (ACB 1050) material was the best adsorbent of this pollutant, reaching an adsorption capacity of 6.43 mmol g−1.

Surface Energy Heterogeneity Profiles of Carbon Nanotubes with a Copolymer-Modified Surface Using Surface Energy Mapping by Inverse Gas Chromatography

The effectiveness and quantitative control of the surface transition of multi-walled carbon nanotubes (MWCNTs) was characterized by inverse gas chromatography (iGC). The surface energy profile of carbon nanotubes compatibilized with an olefin-maleic-anhydride-ester-amide (OMAEA)-type coupling agent was determined by a surface energy analyzer (SEA). The surface energetic heterogeneity with energy distributions of dispersive and specific (acid-base) components of the surface energy of the MWCNTs were determined at various surface coverages. The results of the surface energy mapping showed that surface treatment significantly reduced the dispersive surface energy of MWCNTs and increased the specific surface energy. Furthermore, the surface modification enhanced its Lewis basic character and simultaneously decreased the acidic character of MWCNTs. It has been demonstrated that the surface treatment modified the heterogeneity profiles of the energetic surface of the carbonaceous nanomaterials.

Impact of backbone fluorination on nanoscale morphology and excitonic coupling in polythiophenes

Fluorination represents an important strategy in developing high-performance conjugated polymers for photovoltaic applications. Here, we use regioregular poly(3-ethylhexylthiophene) (P3EHT) and poly(3-ethylhexyl-4-fluorothiophene) (F-P3EHT) as simplified model materials, using single-molecule/aggregate spectroscopy and molecular dynamic simulations, to elucidate the impacts of backbone fluorination on morphology and excitonic coupling on the molecular scale. Despite its high regioregularity, regioregular P3EHT exhibits a rather broad distribution in polymer chain conformation due to the strong steric hindrance of bulky ethylhexyl side chains. This conformational variability results in disordered interchain morphology even between a few chains, prohibiting long-range effective interchain coupling. In stark contrast, the experimental and molecular dynamic calculations reveal that backbone fluorination of F-P3EHT leads to an extended rod-like single-chain conformation and hence highly ordered interchain packing in aggregates. Surprisingly, the ordered and close interchain packing in F-P3EHT does not lead to strong excitonic coupling between the chains but rather to dominant intrachain excitonic coupling that greatly reduces the molecular energetic heterogeneity.