Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors.

Charge carrier dynamics in an organic semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements, reorganization energies, and driving forces, which vary as a function of position and orientation of the molecules. The exact evaluation of these contributions in a molecular assembly is computationally prohibitive.

Charge transport in columnar mesophases of carbazole macrocycles.

Charge transport properties of a columnar mesophase of carbazole macrocycles are analyzed. Realistic morphologies are sampled using all-atom molecular dynamics simulations while charge transport is simulated using the kinetic Monte Carlo method with transfer rates obtained from the high temperature nonadiabatic limit of Marcus theory. It is shown that the molecular design with side chains pointing inside the macrocycle allows close approach between molecules of neighboring columns, thus enabling three-dimensional transport and helping to circumvent charge trapping on structural defects.

Charge transport in organic crystals: role of disorder and topological connectivity.

We analyze the relationship among the molecular structure, morphology, percolation network, and charge carrier mobility in four organic crystals: rubrene, indolo[2,3-b]carbazole with CH(3) side chains, and benzo[1,2-b:4,5-b']bis[b]benzothiophene derivatives with and without C(4)H(9) side chains. Morphologies are generated using an all-atom force field, while charge dynamics is simulated within the framework of high-temperature nonadiabatic Marcus theory or using semiclassical dynamics. We conclude that, on the length scales reachable by molecular dynamics simulations, the charge transport in bulk molecular crystals is mostly limited by the dynamic disorder, while in self-assembled monolayers the static disorder, which is due to the slow motion of the side chains, enhances charge localization and influences the transport dynamics.

Columnar mesophases of hexabenzocoronene derivatives. I. Phase transitions.

Using atomistic molecular dynamic simulations we study the transitions between solid herringbone and liquid crystalline hexagonal mesophases of discotic liquid crystals formed by hexabenzocoronene derivatives. Combining a united atom representation for the side chains with the fully atomistic description of the core, we study the effect of side chain substitution on the transition temperatures as well as molecular ordering in the mesophases. Our study rationalizes the differences in charge carrier mobilities in the herringbone and hexagonal mesophases, which is predominantly due to the better rotational register of the neighboring molecules.

Spider silk softening by water uptake: an AFM study.

We have investigated the mechanical properties of spider dragline fibers of three Nephila species under varied relative humidity. Force maps have been collected by atomic force microscopy. The Young's modulus E was derived from the indentation curves of each pixel by the modified Hertz model.