Discotic liquid crystals are a promising class of materials for molecular electronics thanks to their self-organization and charge transporting properties. The best discotics so far are built around the coronene unit and possess six-fold symmetry. In the discotic phase six-fold-symmetric molecules stack with an average twist of 30 degrees, whereas the angle that would lead to the greatest electronic coupling is 60 degrees. Here, a molecule with three-fold symmetry and alternating hydrophilic/hydrophobic side chains is synthesized and X-ray scattering is used to prove the formation of the desired helical microstructure. Time-resolved microwave-conductivity measurements show that the material has indeed a very high mobility, 0.2 cm(2) V(-1) s(-1). The assemblies of molecules are simulated using molecular dynamics, confirming the model deduced from X-ray scattering. The simulated structures, together with quantum-chemical techniques, prove that mobility is still limited by structural defects and that a defect-free assembly could lead to mobilities in excess of 10 cm(2) V(-1) s(-1).

Although experimental and theoretical studies have addressed the question of the wetting properties of graphene, the actual value of the contact angle of water on an isolated graphene monolayer remains unknown. While recent experimental literature indicates that the contact angle of water on graphite is in the range 90-95°, it has been suggested that the contact angle on graphene may either be as high as 127° or moderately enhanced in comparison with graphite. With the support of classical molecular dynamics simulations using empirical force-fields, we develop an argumentation to show that the value of 127° is an unrealistic estimate and that a value of the order of 95-100° should be expected. Our study establishes a connection between the variation of the work of adhesion of water on graphene-based surfaces and the interaction potential between individual water molecules and these surfaces. We show that a variation of the contact angle from 90° on graphite to 127° on graphene would imply that both of the first two carbon layers of graphite contribute approximately the same interaction energy with water. Such a situation is incompatible with the short-range nature of the interaction between water and this substrate. We also show that the interaction potential energy between water and the graphene-based substrates is the main contribution to the work of adhesion of water with a relative magnitude that is independent of the number of graphene layers. We introduce the idea that the remaining contribution is entropic in nature and is connected to the fluctuations in the water-substrate interaction energy.

A correlation is established between the molecular structure and charge mobility of discotic mesophases of hexabenzocoronene derivatives by combining electronic structure calculations, molecular dynamics, and kinetic Monte Carlo simulations. It is demonstrated that this multiscale approach can provide an accurate ab initio description of charge transport in organic materials.

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Discotic mesophases are known for their ability to self-assemble into columnar structures and can serve as semiconducting molecular wires. Charge carrier mobility along these wires strongly depends on molecular packing, which is controlled by intermolecular interactions. By combining wide-angle X-ray scattering experiments with molecular dynamics simulations, we elucidate packing motifs of a perylene tetracarboxdiimide derivative, a task which is hard to achieve by using a single experimental or theoretical technique. We then relate the charge mobility to the molecular arrangement, both by pulse-radiolysis time-resolved microwave conductivity experiments and simulations based on the non-adiabatic Marcus charge transfer theory. Our results indicate that the helical molecular arrangement with the 45 degrees twist angle between the neighboring molecules favors hole transport in a compound normally considered as an n-type semiconductor. Statistical analysis shows that the transport is strongly suppressed by structural defects. By linking molecular packing and mobility, we eventually provide a pathway to the rational design of perylenediimide derivatives with high charge mobilities.

Systematically coarse grained models for complex fluids usually lack chemical and thermodynamic transferability. Efforts to improve transferability require the development of effective potentials with unequivocal physical significance. In this paper, we introduce conditional reversible work (CRW) potentials that describe nonbonded interactions in coarse grained models at the pair level. The method used to obtain these potentials is straightforward to implement, can be readily extended to compute hydration contributions in implicit-solvent potentials, and is easy to automize. As a first illustration of the method, we present CRW potentials for 3-site models of hexane and toluene. The temperature-transferability of the liquid phase density obtained with these potentials has been investigated, and a comparison has been made with effective potentials obtained by the iterative Boltzmann inversion method.

The increasing interest in room-temperature ionic liquids (RTILs) is related to their possible exploitation as environmentally friendly neoteric solvents because of their vanishing vapor pressure, thermal and chemical stability, air and moisture stability, wide liquidus range, solvent capability. Suitable applications of RTILs in synthesis, catalysis, biocatalysis, material science, and chemical engineering have been reported.[1] The rapidly increasing number and relevance of applications stimulated deeper understanding of the structure of RTILs in terms of intermolecular interactions that take place in the bulk liquid at the atomic level.[2] In such a context, the nuclear overhauser effect (NOE) is a powerful investigative tool, as it originates from dipolar interaction between pairs of nuclei and thus provides information on the molecular sites involved in the interactions. A pioneering study by Osteryoung and co-workers [3] demonstrated the existence of intermolecular NOE interactions between ring protons in 1-ethyl-2-methylimidazolium [EMIM]Cl·AlCl 3 . The cation-cation contacts suggested a local or short-range structure of the liquid. The concept of a local structure in liquid methylimidazolium salts that resembles those found in the solid state has been stressed by some authors on the basis of X-ray diffraction, [4] neutron scattering, [5] and NMR spectroscopy.[6]Herein, we present the first attempt to provide cationcation distances in neat liquid 1-butyl-3-methylimidazolium tetrafluoroborate ( À (2 g), which bear a bulky and noncoordinating anion, possibly because of the effect of increased intercation distance rather than unfavorable correlation times. The methodology for the assessment of distances in the liquid relies upon the distance dependence of the crossrelaxation rate s obtained by intermolecular NOE build-up rates. [7] The cations 1 a and 2 a can be depicted as a polar head (the charged imidazolium ring) and an apolar tail (the n-butyl chain). NOESY spectra showed both head-to-head and headto-tail cation-cation contacts. Herein, we assume that a) the tumbling of the system is isotropic and can be described by a single correlation time and b) the contact time of the cationcation association is long enough to contribute to dipolar relaxation. These are reasonable hypotheses for head-to-head contacts and could be verified if individual correlation times À (2). Curved arrows and Greek letters refer to the torsion angles of the butyl chain. b) Effective correlation times t eff (ns) at 305 K for 1 a and 315 K for 2 a. Tf= triflate.

We present the results of an extensive test of different force field models for crystalline oligothiophenes. The models are mostly based on MM3 for intramolecular degrees of freedom, but they rely on ab initio calculations for the inter-ring torsion potential and the molecular charge distribution. The latter is represented using either point charges from a fit of the molecular electrostatic potential or atomic charges, dipoles, and quadrupoles from a distributed multipole analysis. The force fields are tested by comparing the experimental structures with static energy minimizations and, in a few cases, room-temperature molecular dynamics simulations, also. We find that the point-charge model yields satisfactory results for most systems, including α-tetrathiophene, α-sexithiophene, tetrahexylsexithiophene, and bis(dithienothiophene). However, α-perfluorosexithiophene represents one difficult case where the distributed multipole model turns out to be clearly superior. Finally, we find that it is necessary to rescale the MM3 van der Waals parameters when these are employed in molecular dynamics simulations to reproduce the correct crystal densities.