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Hole transport properties are modeled for two polymorphs of pentacene: the single crystal polymorph and the thin film polymorph relevant for organic thin-film transistor applications. Electronic couplings are evaluated in the standard dimer approach but also considering a cluster approach in which the central molecule is surrounded by a large number of molecules quantum-chemically described. The effective electronic couplings suitable for the parametrization of a tight-binding model are derived either from the orthogonalization scheme limited to HOMO orbitals and from the orthogonalization of the full basis of molecular orbitals. The angular dependent mobilities estimated for the two polymorphs using the predicted pattern of couplings display different anisotropy characteristics as suggested from experimental investigations.

The charge transport properties of two fused-ring thienoacenes, (a) the syn-isomer of dibenzo-thieno-dithiophene (DBTDT), packing in the solid state with a π–π stacking arrangement and also known as bis-benzo-thieno-thiophene (BBTT) and (b) C6-DBTDT, an alkylated derivative, packing in the more conventional herring-bone arrangement, are investigated computationally in the framework of the non-adiabatic hopping mechanism. Charge transfer rate constants are computed within the Marcus–Levich–Jortner formalism including a single effective mode treated quantum mechanically and are injected in a kinetic Monte Carlo scheme to propagate the charge carrier in the crystal. Charge mobilities are computed at room temperature with and without the influence of an electric field and are shown to compare very well with the measured mobilities in single-crystal devices. Both systems show an almost 1D charge transport with C6-DBTDT displaying about a ten times larger mobility value, in agreement with experiment. It is shown that the role of the HOMO-1 orbital is not relevant for BBTT, while it might contribute to a more marked 2D charge transport character for C6-DBTDT.