Electron transfer through a single barrier inside a molecule: from strong to weak coupling

In all theoretical treatments of electron transport through single molecules between two metal electrodes, a clear distinction has to be made between a coherent transport regime with a strong coupling throughout the junction and a Coulomb blockade regime in which the molecule is only weakly coupled to both leads. The former case where the tunnelling barrier is considered to be delocalized across the system can be well described with common mean-field techniques based on density functional theory (DFT), while the latter case with its two distinct barriers localized at the interfaces usually requires a multideterminant description. There is a third scenario with just one barrier localized inside the molecule which we investigate here using a variety of quantum-chemical methods by studying partial charge shifts in biphenyl radical ions induced by an electric field at different angles to modulate the coupling and thereby the barrier within the $\pi$-system. We find steps rounded off at the edges in the charge versus field curves for weak and intermediate coupling, whose accurate description requires a correct treatment of both exchange and dynamical correlation effects is essential. We establish that DFT standard functionals fail to reproduce this feature, while a long range corrected hybrid functional fares much better, which makes it a reasonable choice for a proper DFT-based transport description of such single barrier systemsComment: 8 pages, 4 figures; J. Chem. Phys., in print (2012

Effect of an external electric field on the charge transport parameters in organic molecular semiconductors

© 2003 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.1625918DOI: 10.1063/1.1625918Internal reorganization energies and interchain transfer integrals are two key parameters governing the charge-transport properties of organic semiconducting materials. Here, in order to model some aspects of device operation in field-effect transistors based on conjugated oligomers, we investigate via semiempirical quantum-chemical calculations the way these two parameters are modified when a static electric field in the range 10⁶–10⁸ V/cm is applied along the long axis of pentacene and sexithienyl molecules. For the highest fields, a pronounced redistribution of the charges along the oligomer chains occurs, which is accompanied by significant geometric distortions. However, these charge redistribution effects are found not to impact significantly the transport parameters

Multiscale Modelling of Organic and Hybrid Photovoltaics

VIII, 400 p. 147 illus., 113 illus. in color.onli

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Fluorescence light emission at 1 eV from a conjugated polyme

A cross-circulation approach for tuning the initial dialogue between recipient leukocytes and donor lung graft cells in the pig preclinical model

International audienc

Three-dimensional band structure and bandlike mobility in oligoacene single crystals: A theoretical investigation

© 2003 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.1539090DOI: 10.1063/1.1539090Quantum-chemical calculations coupled with a tight binding band model are used to study the charge carrier mobilities in oligoacene crystals. The transfer integrals for all nonzero interactions in four crystalline oligoacenes ~naphthalene, anthracene, tetracene, and pentacene! were calculated, and then used to construct the excess electron and hole band structures of all four oligoacene crystals in the tight binding approximation. From these band structures, thermal-averaged velocity– velocity tensors in the constant-free-time and the constant-free-path approximations for all four materials were calculated at temperatures ranging from 2 to 500 K. The bandwidths for these oligoacenes were found to be of the order of 0.1–0.5 eV. Furthermore, comparison of the thermal-averaged velocity–velocity tensors with the experimental mobility data indicates that the simple band model is applicable for temperatures only up to about 150 K. A small-polaron band model is also considered, but the exponential band narrowing effect is found to be incompatible to experimental power law results

Optical properties of light-emitting nematic liquid crystals: A joint experimental and theoretical study

Semiempirical quantum-chemical calculations are used to simulate the optical properties of a series of green light-emitting nematic liquid crystals containing fluorene, thiophene, or thienothiophene groups with solid-state photoluminescence quantum efficiencies up to 0.36. We use a simple model of two parallel and closely spaced molecules in an anticofacial configuration to study intermolecular interactions in the solid state and slide one past the other to mimic the high orientational and low positional order of the nematic phase. We find that switching between H and J aggregates can be triggered by longitudinal displacements of the molecules with respect to one another by an extent that closely follows the chemical structure of the interacting chromophores. We discuss the implications of aggregate formation for efficient light emission in conjugated oligomers and polymers that show nematic or smectic order. © 2010 American Chemical Society

Self-assembly of an asymmetrically functionalized [6]helicene at liquid/solid interfaces

STM brings to light chirality aspects of the self-assembly of a functionalized helicene at the interface between a liquid and the solid substrates, gold and graphite. This reveals conditions for conglomerate formation.status: publishe