Acenes comprise an important class of organic semiconducting materials. As graphene nanoribbons of ultimate width, they are valuable atom-precise model systems for studying the properties of this form of nanoscale carbon materials. Heptacene is the smallest member of the acene series that could only be studied under matrix isolation conditions. Its existence in bulk had never been positively confirmed, despite efforts dating back more than 70 years. We report that the reduction of 7,16-heptacenequinone produces a mixture of two diheptacene molecules. The diheptacenes undergo thermal cleavage to heptacene at high temperatures in the solid state. Monitoring this cycloreversion by solid state C cross-polarized magic angle spinning NMR reveals that solid heptacene has a half-life time of several weeks at room temperature. The diheptacenes are valuable precursors for generating films of heptacene by vapor phase deposition that can be studied below or at room temperature.

Although hexacene was first synthesized in 1939, the thin film properties, which are interesting for future applications and fundamental research, have never been investigated. Therefore, we synthesized hexacene by reduction of 6,15-hexacenequinone, evaporated hexacene, and grew films of variable thicknesses on Au(110). This allowed us to study the electronic properties and molecular orientations in the bulk as well as at the molecule–metal interface by X-ray absorption spectroscopy (XAS) and photoelectron spectroscopy. Valence band spectra of a multilayer hexacene film are compared to those of electronic states obtained from density functional theory calculations. C 1s core-level spectra show typical satellite structures of the extended aromatic π-system, similar to pentacene. XAS shows that anisotropy rises with decreasing film thickness and indicates that hexacene is almost flat lying on the Au(110) substrate. The different peak shapes of XAS spectra as a function of the film thickness, as well as changes in valence band spectra and C 1s satellite structures, indicate a strong electronic coupling of the molecular states with the states of the Au(110) substrate at the interface.

Layered transition metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS2), are currently in the focus of interest due to their novel electronic properties. The adsorption of molecules is a promising way to tune the electronic structure of TMDCs. We study interface properties between MoS2 and differently fluorinated iron phthalocyanines (FePcF x , x = 0, 4, 16) using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), angle-resolved photoelectron spectroscopy (ARPES), and X-ray absorption spectroscopy (XAS). A key parameter for the charge transfer is the ionization potential of FePcF x . A distinct electron transfer from a molecule to a substrate is observed for FePc and FePcF4. From energy-momentum ARPES maps, we suppose that the substrate and FePc-related states hybridize at the interface. This study demonstrates that a controlled tuning of the electronic structure of MoS2 by electron donors is possible, driven by the ionization potential difference between the substrate and the adsorbate.

Interface properties of CoPc and CoPcF16 on Cu-intercalated graphene/Ni(111) were investigated by X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and X-ray absorption spectroscopy (XAS). We show that a charge transfer from graphene/Ni(111) to the Co ion of CoPc can be significantly reduced by Cu-intercalation of graphene, resulting in a partial decoupling of graphene from the Ni(111) substrate. This is not the case for CoPcF16 on Cu-intercalated graphene/Ni(111). Possible reasons and charge transfer channels are discussed. The comparison to CoPcF16 on the almost fully decoupled Au-intercalated graphene/Ni(111) suggests that the graphene-substrate coupling in the case of Cu-intercalation remains still significant.

Electronic interface properties and the initial growth of hexa-peri-hexabenzocoronene with a borazine core (BN-HBC) on Au(111) have been studied by using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A weak, but non-negligible, interaction between BN-HBC and Au(111) was found at the interface. Both hexa-peri-hexabenzocoronene (HBC) and BN-HBC molecules form well-defined monolayers. The different contrast in STM images of HBC and BN-HBC at different tunneling voltages with submolecular resolution can be ascribed to differences in the local density of states (LDOS). At positive and negative tunneling voltages, STM images reproduce the distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) as determined by density functional theory (DFT) calculations very well.