Roland E. Bauer

Single-crystal structures of polyphenylene dendrimers

A series of first-generation polyphenylene dendrimers based on three different cores were prepared by Diels-Alder cycloaddition and their single-crystal structures were determined. Consisting exclusively of interlocked, twisted phenyl rings, these polyphenylene nanostructures have exciting structural and dynamic properties. Single crystals of dendrimers, suitable for X-ray structure analysis, were grown from different solvent mixtures by slow evaporation at room temperature. It should be pointed out that one of the described polyphenylene dendrimers represents up to now the biggest oligophenylene nanostructure from which crystallographic data is available.

Functional polymers as nanoscopic building blocks

Abstract Polyphenylene dendrimers are introduced as polymeric building blocks—with a strictly monodisperse particle size distribution within the nanometer range—for the construction of nanostructured materials and devices. The possibility for the introduction of different functionalities in the core, the scaffold or the periphery of the dendrimers offer their use as interesting modules for photonic, electronic or bioactive structures and supramolecular functional assemblies. Thus, dendrimers complement the available set of nanoscopic building blocks made from metals, e.g., Au nanoclusters and semiconductors, e.g., luminescent quantum dots. In a first set of experiments, we describe the fabrication of multilayer architectures using dendrimers with chargeable groups at the surface. This way, the polyelectrolyte deposition technique can be applied for the construction of hybrid layered assemblies with a control of the internal supramolecular structure at the nanometer level. Surface plasmon field-enhanced fluorescence spectroscopy is used to monitor the luminescent properties of dendrimers with a phthalocyanine core integrated into such a multilayer assembly. AFM and SEM micrographs demonstrate the use of surface-functionalized dendrimers (exposing sulfur groups at the periphery) in combination with Au nanoparticles for the controlled assembly of hybrid aggregates as nanoscopic functional devices.

One-Pot Preparation of Dendrimer−Gold Nanoparticle Hybrids in a Dipolar Aprotic Solvent

We present a simple one-pot, one-step method to obtain stable and nearly monodisperse gold nanoparticles in dipolar aprotic solvents. Novel thiomethyl-functionalized polyphenylene dendrimers are used to control the growth and stabilize the nanoparticles in suspension. The dendrimer functionalized gold nanoparticles have an average size of roughly 10 nm and are stable in suspension for several weeks. The stability in dipolar aprotic solvents and the great functionalization flexibility offered by the dendrimers make these metal/dendrimer hybrid systems promising for applications such as nanophotonics, molecular electronics, and sensing.

Guiding the self-assembly of a second-generation polyphenytene dendrimer into well-defined patterns

A second-generation polyphenylene dendrimer 1 is shown to self-assemble into nanofibers. To guide the formation of the dendrimer fibers into well-defined patterns, 1H,1H,2H,2H-perfluorodecyltrichlorosilane is grafted in the gas phase onto a silicon substrate. De-wetting of the solution on the nanopatterned surface results in the formation of a nanostructured template, into which fiber growth subsequently occurs under the constraints set by the de-wetted morphology.

Optical resonances of gold nanoparticles on a gold surface: quantitative correlation of geometry and resonance wavelength

The optical resonance of gold nanoparticles placed at nanometre distances from a gold surface by means of a dielectric spacer was investigated. Different types of molecules, 2-aminoethanethiol and shape-persistent polyphenylene dendrimers were used as spacers and compared. Furthermore, the gold nanoparticle size and the ambient medium were varied. The influence of all these parameters on the resonance wavelength of the system was determined. Based on a simple analytical model, a quantitative analysis was developed and surprisingly good agreement of this model with our experiment without any adjustable parameters was found.

Positron annihilation study of polyphenylene dendrimers

Abstract The free volume of a series of rigid polyphenylene dendrimers was studied by positron lifetime spectroscopy and the experimental data were compared with results from molecular dynamics calculations. Contrary to dendrimers containing flexible repeat units rigid polyphenylene dendrimers proved to contain large stable “inner” voids of a distinct size between their dendritic branches. The size of the “inner” cavities increases with the size of the dendrimer. Due to these voids, polyphenylene dendrimers are potentially attractive with respect to the selective incorporation of guest molecules.