The novel organic semiconductor dinaphthothienothiophene (DNTT) has gained considerable interest because its large charge carrier mobility and distinct chemical robustness enable the fabrication of organic field effect transistors with remarkable long-term stability under ambient conditions. Structural aspects of DNTT films and their control, however, remain so far largely unexplored. Interestingly, the crystalline structure of DNTT is rather similar to that of the prototypical pentacene, for which the molecular orientation in crystalline thin films can be controlled by means of interface-mediated growth. Combining atomic force microscopy, near-edge X-ray absorption fine structure, photoelectron emission microscopy, and X-ray diffraction, we compare substrate-mediated control of molecular orientation, morphology, and wetting behavior of DNTT films on the prototypical substrates SiO and graphene as well as technologically relevant dielectric surfaces (SiO and metal oxides that were pretreated with self-assembled monolayers (SAMs)). We found an immediate three-dimensional growth on graphene substrates, while an interfacial wetting layer is formed on the other substrates. Rather surprisingly, we observe distinct temporal changes of DNTT thin films on SiO and the SAM-treated dielectric substrates, which exhibit a pronounced dewetting and island formation on time scales of minutes to hours, even under ambient conditions, leading to a breakup of the initially closed wetting layer. These findings are unexpected in view of the reported long-time stability of DNTT-based devices. Therefore, their future consideration is expected to enable the further improvement of such applications, especially since these structural modifications are equivalently observed also on the SAM-treated dielectric surfaces, which are commonly used in device processing.

Interfaces between pentacene and Buckminster‐fullerene (C60) have attracted interest due to their application as oligomeric model system for organic solar cells. As the actual device characteristics in such implementations are crucially controlled by the interface structure, detailed investigations of this interface on a molecular level are mandatory. In this study, the influence of the orientation of the pentacene molecules in highly ordered crystalline bottom layers on the characteristics of such internal interfaces is analyzed. It has been shown that the interface structure is driven by temperature‐controlled diffusion of C60 molecules to the pentacene step edges in the case of uprightly oriented pentacene. For lying pentacene in the bottom layer, no step‐edge decoration is observed while the wetting of the pentacene layer is enhanced. Furthermore, the stability of the interface against intercalation and reorientation has been analyzed by means of NEXAFS spectroscopy, showing that the orientation of the pentacene molecules at the interface remains unchanged. Instead, strong indication for chemical modification of the molecular entities by the formation of Diels–Alder adducts between C60 and pentacene is observed. Finally, it is shown that C60 forms crystalline islands in thicker films only on top of uprightly oriented pentacene while rather amorphous films are formed on lying pentacene.

The polarization-resolved absorption spectra are determined for different pentacene polymorphs, both, for thin films grown on ZnO as well as for free-standing single crystals. A clear interrelation between the Davydov splitting of the lowest-energy singlet-exciton type transitions and the herringbone angle of the molecules in the unit cell is found. The variation in oscillator strength of the individual excitonic Davydov components with temperature is explained by a variation of this herringbone angle. The extraordinarily strong variation of the herringbone angle for Campbell phase pentacene films grown on ZnO substrates is attributed to interface-mediated strain due to the different thermal expansion coefficients of the organic and inorganic constituents.

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