| Abstract
| - Discotic molecules have planar, disklike polyaromatic cores that can self-assemble into “molecularwires”. Highly anisotropic charge transfer along the wires arises when there is sufficient intermolecularoverlap of the π-orbitals of the molecular cores. Discotic materials can be applied in molecular electronics,field-effect transistors, andrecently with record quantum efficienciesphotovoltaics (Schmidt-Mende, L.;Fechtenkötter, A.; Müllen, K.; Moons, E.; Frien, R. H.; MacKenzie, J. D. Science2001, 293, 1119). Acombination of quasielastic neutron scattering (QENS) measurements with molecular dynamics simulationson the discotic molecule hexakis(n-hexyloxy)triphenylene (HAT6) shows that the dynamics of the coresand tails of discotic molecules are strongly correlated. Core and tail dynamics are not separated, the systembeing characterized by overall in-plane motion, on a time scale of 0.2 ps, and softer out-of-plane motionsat 7 ps. Because charge transfer between the molecules is on similar time scales, these motions are relevantfor the conducting properties of the materials. Both types of motion are dominated by van der Waalsinteractions. Small-amplitude in-plane motions in which the disks move over each other are almost entirelydetermined by tail/tail interactions, these also playing an important role in the out-of-plane motion. TheQENS measurements reveal that these motions are little changed by passing from the columnar phase tothe isotropic liquid phase, just above the clearing temperature. The model of four HAT6 molecules in acolumn reproduces the measured QENS spectrum of the liquid phase, suggesting that correlations persistwithin the liquid phase over about this number of disks.
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