Organic-organic epitaxy is a successful strategy for growing highly oriented and crystalline heterojunctions of organic semiconductors. Within this class of materials, crystalline rubrene is especially promising because of its outstanding hole mobility. Here, the (200) surface of rubrene single crystals was used as substrate for growing thin films of another organic semiconductor: R-quaterthiophene. The film growth proceeds via a 3D mechanism, with the formation of a fewmonolayer-thick crystalline islands oriented along two main directions, as deduced by the optical reflection of the R-quaterthiophene/rubrene heterostructure measured over macroscopic regions. An atomic-scale analysis of the film surface performed with scanning force microscopy revealed a complete textural order achieved through a line-on-line epitaxial relation. With the help of empirical force-field calculations of the heteroepitaxial interface, this orienting propensity is demonstrated to be strictly related to the peculiar corrugation of the rubrene crystal surface, showing marked furrows along two orthogonal crystallographic directions.

Stable rubrene derivatives displaying the same crystal packing features as orthorhombic rubrene are synthesized and their solid state properties studied.

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The transverse component of the friction forces acting on the tip of an atomic force microscope scanning on the surface of an organic crystal was monitored as a function of the scan direction. The relation between friction and the crystallographic system is disclosed, revealing that the symmetry of the friction phenomenon is dictated by the direction of the prominent corrugations of the crystal surface. It is also illustrated that molecular-resolution images can be collected through the monitoring of the motion of the tip in a transverse direction with respect to the scan direction.