No abstract

The synthesis of a series of molecular rods 1–5, designed to bridge the gap of a carbon nanotube junction in order to emit light as a characteristic signal of integrated molecules, is reported. The molecular rods consist of a central naphthalenediimide (NDI) core, which itself is substituted with benzylamino and benzylsulfanyl groups, providing distinct absorption and emission properties. The NDI core is embedded in an oligo(phenylene ethynylene) (OPE) system providing the rod‐like structure required to bridge gaps between nanoelectrodes. The number of repeating units of the OPE is varied to adjust the length of the target compounds between 2.3 and 6.6 nm. The OPE parts are terminally functionalized with polyaromatic hydrocarbon groups (naphthalene, phenanthrene, anthracene or pyrene), which possess affinity with the surface of the carbon nanotubes due to van der Waals interactions. Synthetic protocols based on Sonogashira–Hagihara couplings were developed to build up the OPE backbone. Bifunctional iodophenyl acetylene derivative 33 served as a key building block in a coupling–deprotecting–coupling sequence. The NDI building block was synthesized by an aromatic nucleophilic substitution reaction of 2,6‐dichloro‐1,4,5,8‐tetracarboxylic acid naphthalenediimide derivative 9 and the corresponding amine and sulfide (i.e., 11, 12), respectively. The convergent synthesis allows modular assembly of the NDI and OPE parts in a final Sonogashira–Hagihara coupling reaction. The target structures were fully characterized by NMR spectroscopy and mass spectrometry. Further, the optical properties of compounds 3–5 in solution, and on a graphene surface were qualitatively investigated. A Dexter‐type energy transfer from the OPE unit to the NDI unit was observed. The studies of target structures 3–5 revealed that diamino‐functionalized compound 3 is ideally suited for the envisaged single molecule electroluminescence experiments.

Studying the stepwise assembly of a four component hybrid structure on Au(111)/mica, the pores of a hydrogen bonded bimolecular network of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine) were partitioned by three and four-armed molecules based on oligo([biphenyl]-4-ylethynyl)benzene, followed by the templated adsorption of either C60 fullerene or adamantane thiol molecules. The characterisation by ambient scanning tunneling microscopy (STM) reveals that the pore modifiers exhibit dynamics which pronouncedly depend on the molecular structure. The three-armed molecule 1,3,5-tris([1,1′-biphenyl]-4-ylethynyl)benzene (3BPEB) switches between two symmetry equivalent configurations on a time scale fast compared to the temporal resolution of the STM. Derivatisation of 3BPEB by hydroxyl groups substantially reduces the switching rate. For the four-armed molecule configurational changes are observed only occasionally. The observation of isolated fullerenes and small clusters of adamantane thiol molecules, which are arranged in a characteristic fashion, reveals the templating effect of the trimolecular supramolecular network. However, the fraction of compartments filled by guest molecules is significantly below one for both the thermodynamically controlled adsorption of C60 and the kinetically controlled adsorption of the thiol with the latter causing partial removal of the pore modifier. The experiments, on the one hand, demonstrate the feasibility of templating by nested assembly but, on the other hand, also pinpoint the requirement for the energy landscape to be tolerant to variations in the assembly process.

Trigonal molecules compartmentalise the pores of a honeycomb network of 3,4:9,10-tetracarboxylic diimide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine). Extending the 1,3,5-tri(phenylene-ethynylene)benzene core by a phenyl group allows for a well-defined accommodation of the molecule into two symmetry equivalent positions in the pore. The corresponding styryl or phenylene-ethynylene derivatives exceed the pore size and, thus, impede pore modification.

A detailed scanning tunneling microscopy (STM) study of two variants of oligo(phenylene ethynylene) (OPE) molecules is presented. These molecules might serve as molecular wires up to ≈ 5 nm in length. Self-assembled arrangements as well as single molecules on a Au(111) surface were analyzed. The molecular orbitals were directly imaged and are compared to density functional theory calculations. Sub-molecular resolution images of both molecules directly display the chemical structure. One of the OPE variants was lifted off the surface by the STM tip to measure the singlemolecule conductance in order to explain previously reported low conduction values. Furthermore, we present a detailed analysis of a tip-induced conformational switching of the hexyl side groups from all-trans to a nonlinear conformation, which was observed for both variants.