A light-addressable gold electrode modified with CdS and FePt or with CdS@FePt nanoparticles via an interfacial dithiol linker layer is presented. XPS measurements reveal that trans-stilbenedithiol provides high-quality self-assembled monolayers compared to benzenedithiol and biphenyldithiol, in case they are formed at elevated temperatures. The CdS nanoparticles in good electrical contact with the electrode allow for current generation under illumination and appropriate polarization. FePt nanoparticles serve as catalytic sites for the reduction of hydrogen peroxide to water. Advantageously, both properties can be combined by the use of hybrid nanoparticles fixed on the electrode by means of the optimized stilbenedithiol layer. This allows a light-controlled analysis of different hydrogen peroxide concentrations.

The molecular packing motifs occurring in the crystal structures of pentacene and its two oxo-derivatives (6,13pentacenequinone and 5,7,12,14-pentacenetetrone) have been analyzed. Both oxygen containing species exhibit an almost coplanar stacking while pentacene adopts a face-on-edge herringbone packing. The different packing motifs are well explained by quantum chemical ab initio calculations of the electronic structure of the molecular entities exhibiting a pronounced charge localization at the oxygen atoms of both oxo-derivatives which causes an additional electrostatic O-π interaction favoring a planar stacking. Moreover, the polarizability of the π-system is reduced and the molecular quadrupole moment is altered, both resulting in a decrease of the lattice energy of the oxo-species as evidenced by the sublimation energy obtained for all three species from thermal desorption measurements. This emphasizes the importance of the balance between electrostatic and van der Waals interactions for the packing in molecular crystals.

The optical transitions of pentacene films deposited on ZnO have been studied by absorption spectroscopy as a function of temperature in the range of room temperature down to 10 K. The pentacene films were prepared with thicknesses of 10 nm, 20 nm, and 100 nm on the ZnO-O(000-1) surface by molecular beam deposition. A unique temperature dependence has been observed for the two Davydov components of the excitons for different film thicknesses. At room temperature, the energetic positions of the respective absorption bands are the same for all films, whereas the positions differ more than 20 meV at 10 K caused by the very different expansion coefficients of pentacene and ZnO. Although the pentacene is just bonded via van der Waals interaction to the ZnO substrate, the very first pentacene monolayer (adlayer) is forced to keep the initial position on the ZnO surface and suffering, therefore, a substantial tensile strain. For all the subsequent pentacene monolayers, the strain is reduced step by step resulting electronically in a strong potential gradient at the interface.

Rubrene single crystals were grown by deposition near thermal equilibrium conditions which yields distinct microcrystals with sizes up to 100 μm. Such crystallites are rather spherical and exhibit various low index surfaces which enable detailed surface studies as well as directional-dependent bulk measurements. The analysis of the crystal habit reveals characteristic geometries for the confining surfaces which offer an unambiguous identification of their orientation. Atomic force microscopy (AFM) measurements demonstrate that the surfaces of the crystallites are ultraflat with a very low density of defects which is accompanied by a pronounced stability against oxidation at ambient conditions as inferred from laser desorption ionization time-of-flight mass spectroscopy (LDI-TOF MS). To exemplify the ability of such crystals to investigate bulk anisotropies, the refractive index tensor of rubrene was precisely determined at a wavelength of λ = 589 nm by employing the Becke line method.

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Pentacene films have been grown on two polar zinc oxide surfaces, i.e., ZnO(0001) and ZnO(0001(-)), as well as on the mixed-terminated ZnO(101(-)0) and are characterized by means of atomic force microscopy (AFM), x-ray diffraction (XRD), and thermal desorption spectroscopy (TDS). In all cases, pentacene aggregates in an upright orientation without any evidence for the formation of an interface stabilized wetting layer. Additional films deposited on a highly-defective, oxygen-depleted ZnO(0001(-)) reveal no altered growth mode. Nearly identical optical absorption spectra have been measured for all films, thus corroborating a weak molecule-substrate interaction. Upon cooling, however, a slightly different relaxation behavior could be resolved for pentacene films on polar ZnO surfaces compared to pentacene on the mixed-terminated ZnO(101(-)0) surface.