Solvent Thermodynamic Driving Force Controls Stacking Interactions between Polyaromatics

Abstract

Polyaromatic dye molecules employed in photovoltaic and electronic applications are often processed in organic solvents. The aggregation of these dyes is key to their applications, but a fundamental molecular understanding of how the solvent environment controls the stacking of polyaromatics is unclear. This study reports initial results from Monte Carlo simulations of how various acene molecule dimers stack when they are dissolved in different solvents. Free energies computed using full dispersion interactions versus those with sterics only suggest that solvent entropy alone accounts for the majority of the stacking free energy in solvents with compact molecular geometries such as carbon tetrachloride. However, in contrast with carbon tetrachloride, we also observe significant variations in the stacking free energies of naphthalene, anthracene, and tetracene across other solvents such as toluene and cyclohexane. The weak attractive dispersion interactions between the acene solutes and planar and near-planar solvent molecules enable them to intercalate between the acene monomers, inducing extra stability beyond what solvent entropic driving force alone could predict. In all three solvents studied (carbon tetrachloride, cyclohexane, toluene) the solvent environment helps facilitate stacking of all three acenes studied (naphthalene, anthracene, tetracene), inducing a significant stabilization free energy between −4 and −8 kcal/mol. Extensive free energy umbrella sampling along the other orthogonal directions allows us to accurately calculate the dimerization equilibrium constants of all three acenes, which vary over several orders of magnitude in a way that depends intricately on the solvent they are in. Given the prevalence of solution-based processing techniques for organic electronic and photonic devices, these results provide useful insights into the critical role that solvent structure and characteristics play in the solution-based aggregation of organic dyes.

Size-dependent rate acceleration in the silylation of secondary alcohols: the bigger the faster

“…Hence, the observed solvent effects are due to the significant impact of solvents on size-dependent effects, which was also reported in other studies. 26 , 27 , 43 – 46 Distinguishing the different contributions of polarizability (π* and δ), hydrogen-bond donor (α) and acceptor ability (β) via the linear solvation energy relationship developed by Kamlet and Taft 47 , 48 revealed that solvent effects are widely independent of the polarizability of the solvent, but correlate strongly with the hydrogen bond donor ability of the solvent (see eqn (S12) of ESI † ). This can actually be further condensed to a direct correlation of the experimental k rel values with the general α parameter proposed by Hunter ( Fig.…”

Topological Constraints and Their Conformational Entropic Penalties on RNA Folds

“…Unlike molecular dynamics, Nucleic MC can sum over a massive number of backbone conformations with numerical efficiencies that are orders of magnitude faster, enabling a diverse ensemble of chain conformations to be generated rapidly. To further cut down on central processing unit requirements, Nucleic also uses high-level theoretical models (38, 39, 40, 41, 42, 43) to represent the solvent’s and the counterions’ influences on the nucleic acid implicitly without the need of explicitly including solvent molecules and/or counterions in the simulation. Using our in-house parallel-computing resources, a thermal ensemble consisting of several million uncorrelated chain conformations for RNA and DNA sequences of up to 100 nts could be simulated in several days.…”

Aggregation Behavior of Model Asphaltenes Revealed from Large-Scale Coarse-Grained Molecular Simulations

“…In a contribution which is very relevant to this study, von Lilienfeld and Andrienko 44 coarse-grain polycyclic aromatic hydrocarbons by fitting effective Lennard-Jones potentials to density-functional theory calculations, showing that the potential parameters of the CG units are specific to the aromatic molecule in the study. Diverse theoretical and simulation studies related to the understanding of PAHs energetics can be found in the literature [68][69][70][71][72][73] . The specialized discussion of self-organization of the polyaromatic cores into π−π electron-bonded stacks is beyond the scope of this manuscript but some remarks of its importance in asphaltene dimerization are included in the review presented by Adams 19 .…”