Research Overview:

The research focus of the group is geared towards bottom-up approaches to nanotechnology, inter-disciplinary experiments between chemistry and physics and new materials with tailored properties. However, the main expertise and skills of the group remains preparative chemistry and organic synthesis. As an example, the synthesis of a Molecular Rods Comprising a Central Core-Substituted Naphthalenediimide Chromophore from small, commercially available starting materials is outlined below.

Sergio Grunder, David Muñoz Torres, Christoph Marquardt, Alfred Blaszczyk, Ralph Krupke, Marcel Mayor
Synthesis and optical properties of molecular rods comprising a central core-substituted napthalenediimide chrmophore for carbon nanotube junctions
Eur. J. Org. Chem. 2011, 478-496.

Christoph W. Marquardt, Sergio Grunder, Alfred Blaszczyk, Simone Dehm, Frank Hennrich, Hilbert v. Löhneysen, Marcel Mayor, Ralph Krupke
Electroluminescence from a single nanotube-molecule-nanotube junction
Nature Nanotechnology, 2010, 5, 863-867.

Nicolas M. Jenny, Marcel Mayor, Thomas R. Eaton
Phenyl–Acetylene Bond Assembly: A Powerful Tool for the Construction of Nanoscale Architectures
Eur. J. Org. Chem. 2011, 4965-4983.

Molecular Electronics

Integration of molecular structures as active components in electronic circuits is, at the same time, a visionary concept and a scientific challenge. The chemistry job is the design and the synthesis of tailored molecular structures for both, the envisaged experiment and also particular electronic functions.

Since nearly one decade the group has explored the integration of single molecules as functional units in electronic circuits. While in the beginning their studies were limited to the comparison of solely two molecules differing in a structural property like e.g. symmetry or the position of the anchor groups, their recent investigations are based on entire families of molecules systematically varying in a single structural feature.

Torsion Angle Dependence in a Single Molecule Biphenyl Junction

The torsion angle between both phenyl rings of the biphenyl skeleton was systematically varied within the series of cyclophanes displayed in Fig.1 by varying the length of the second bridging alkyl chain. The delocalization of the biphenyl  p-system depends on the torsion angle which is reflected in numerous physical properties such as the electronic absorption properties, the NLO efficiency or the single molecule transport features.

David Vonlanthen, Alexander Rudnev, Artem Mischenko, Alexander Käslin, Jürgen Rotzler, Markus Neuburger, Thomas Wandlowski, Marcel Mayor
Conformationally Controlled Electron Delocalization in n-Type Rods: Synthesis, Structure, and Optical, Electrochemical, and Spectroelectrochemical Properties of Dicyanocyclophanes
Chem. Eur. J., 2011, 17, 7236-7250.

Li Cui, Bo Liu, David Vonlanthen, Marcel Mayor, Yongchun Fu, Jian-Feng Li, Thomas Wandlowski
In situ gap-mode raman spectroscopy on single-crystal Au(100) electrodes: tuning the torsion angle of 4,4'-biphenyldithiols by an electrochemical gate field
J. Am. Chem. Soc., 2011, 133, 7332-7335.

Artem Mischenko, Linda A. Zotti, David Vonlanthen, Marius Bürkle, Fabian Pauly, Juan Carlos Cuevas, Marcel Mayor, Thomas Wandlowski
Single-Molecule junctions based on nitrile-terminated biphenyls: A promising new anchoring group
J. Am. Chem. Soc., 2011, 133, 184-187.

Artem Mishchenko, David Vonlanthen, Velimir Meded, Marius Bürkle, Chen Li, Ilya V. Pobelov, Alexei Bagrets, Janne K. Viljas, Fabian Pauly, Ferdinand Evers, Marcel Mayor, Thomas Wandlowski
Influence of Conformation on Conductance of Biphenyl-Dithiol Single-Molecule Contacts
Nano Lett. 2010, 10, 156-163.

David Vonlanthen, Jürgen Rotzler, Markus Neuburger, Marcel Mayor
Synthesis of Rotationally Restricted and Modular Biphenyl Building Blocks
Eur. J. Org. Chem. 2010, 120-133.

David Vonlanthen, Artem Mishchenko, Mark Elbing, Markus Neuburger, Thomas Wandlowski, Marcel Mayor
Chemically Controlled Conductivity: Torsion-Angle Dependence in a Single-Molecule Biphenyldithiol Junction
Angew. Chem. Int. Ed.. 2009, 48, 8886-8890.

 

New Hybrid Materials

A new research project merges the promising physical properties of nanoparticles with the ordering power of supramolecular chemistry. Organic ligands are designed to wrap around nanoparticles of a particular size. Gold Nanoparticles (Au NPs) are interesting building blocks for future applications in molecular electronics. They can be used as metal electrodes to contact molecular electronic junctions. Because of their size dependent physical properties Au NPs are promising model compounds for a bottom up approach to use them as capacitor in molecular electronic devices to store charges.

The concept should allow to control the spatial arrangement as well as the sizes of several nanoparticles and therewith the creation of new functions like directed energy or electron transport. However, to start with, ligands have to be synthesized that form stable and well defined inclusion complexes with nanoparticles.

It is crucial to control the number of functional groups per Au NP in order to have well defined assembly of the NPs in electronic setups. Therefore linear and dendritic multidentate benzyl thioethers were the ligands of choice as each ligand is able to cover a large surface area.

 

After NP formation it is possible to liberate the acetylene and interlink the particles to oligomers by Glaser Hay coupling or perform “click chemistry” by reacting the particles with azides.

 

Hermes, Jens Peter; Sander, Fabian; Peterle, Torsten; Urbani, Raphael;
Pfohl, Thomas; Thompson, Damien; Mayor, Marcel
Gold Nanoparticles Stabilized by Thioether Dendrimers
Chem. Eur. J.,2011, 17, 13473-13481.

Jens Hermes, Fabian Sander, Torsten Peterle, Marcel Mayor
From ligand-stabilized gold nanoparticles to hybrid organic-inorganic superstructures
Chimia, 2011, 65, 219-222.

Jens Hermes, Fabian Sander, Torsten Peterle, Carla Cioffi, Philippe Ringler, Thomas Pfohl, Marcel Mayor
Direct control of the spatial arrangement of gold nanoparticles in organic-inorganic hybrid superstructures
Small, 2011, 7, 920-929.

Quantum properties of organic molecules

Is there a defined transition between quantum mechanics and classical physics?

Investigations at the interface of the quantum and the classical world is a fascinating part our research. We try to approach the quantum-to-classical transition by the observation of quantum properties of large and complex molecules. In order to observe the wave nature of a molecule - a purely quantum mechanical phenomenon - we developed synthetic procedures towards tailor-made compounds that are optimized for the observation of their wave nature in matter-wave experiments.

With a series of highly fluorinated porphyrins we set a new benchmark in high-mass quantum interference experiments (fig. 2).

Besides the exploration of the limits of matter wave interferometry the second goal is to use quantum interference as a tool for innovative measurements of internal molecular properties such as optical and static polarizabilities, vibration induced or static electric dipole moments, conformational changes and conformational differences as well as molecular fragmentation processes.

Tüxen, Jens; Eibenberger, Sandra; Gerlich, Stefan; Arndt, Markus; Mayor, Marcel
Highly Fluorous Porphyrins as Model Compounds for Molecule Interferometry
Eur. J. Org. Chem. 2011, 4823-4833.

Surface functionnalization & Self assembled monolayers

Physical interactions have their origin at surfaces. Using the tools of synthetic organic chemistry we control the surface morphology at the molecular length scale in order to mediate and study these phenomena. Regulating the interface between bulk material and the surrounding medium affords control of the function of an object by chemically addressing its surface. Solution phase deposition by self-assembly or by electroreduction enables chemical control of the surface morphology.

Synthetic chemistry can be understood as engineering at the nanoscale and allows assembling nanoobjects with very particular physical properties. An example is the synthesis of a molecular ring with a diameter of 12 nm and a periphery consisting exclusively of conjugation-active building blocks.

 

This ring object was designed with regard to its electronic transport - and supramolecular packing properties and will hopefully allow first investigations of persistent currents in organic molecules.  Current activities are geared towards well defined three dimensional objects like tubular systems assembled from molecular rings or ball shaped heteroatom rich macromolecules both designed to display promising electronic and optical properties.

Another endeavor is towards functionalization and patterning of surfaces by self-assembly through Hydrogen bond networks. We are interested in H∙∙∙F H-bonding interactions. Using this as a driving force, we aim at a self-patterned surface network through H∙∙∙F interactions thereby demonstrating the strength of this interaction to drive the self-assembly of cyclic monomers leading to a supramolecular network. The reduced electron density of the aryl units may lead to interesting aggregation properties and the high fluorine content should make the surface hydrophobic.

Responsive monolayers are able to tune the physico-chemical properties of interfaces. A photochromic self assembled monolayer based on a conjugated azobenzene derivative responds to external stimuli modulating the work function of the Au surface. The work function of metallic contacts is important for optimizing charge injection and extraction in electronic devices and hence their performance.

M. Mayor, C. Didschies
A Giant Conjugated Molecular Ring
Angew. Chem. Int. Ed. Engl., 2003, 42, 3176-3179.

Zhongcheng Mu, Lijin Shu, Harald Fuchs, Marcel Mayor, and Lifeng Chi
Two-dimensional self-assembly of linear molecular rods at the liquid/solid interface
Langmuir, 2011, 27(4), 1359-1363.

Faramarzi, V.; Raimondo, C.; Reinders, F.; Mayor, M.; Samori, P.; Doudin, B.
Optically switchable molecular device using microsphere based junctions
Appl. Phys. Lett. 2011, 99, 233104-3.

N. Crivillers, A. Liscio, F. Di Stasio, C. Van Dyck, S. Osella, D. Cornil, S. Mian, G. M. Lazzerini, O. Fenwick,
E. Orgiu, F. Reinders, S. Braun, M. Fahlman, M. Mayor, J. Cornil, V. Palermo, F. Cacialli and P. Samorì,
Photoinduced work function changes by isomerization of a densely packed azobenzene-based SAM on Au:
a joint experimental and theoretical study
Phys. Chem. Chem. Phys., 2011, 13 (32), 14302 - 14310

Núria Crivillers, Emanuele Orgiu, Federica Reinders, Marcel Mayor, Paolo Samori
Optical Modulation of the charge injection in an organic field-effect transistor based on photochromic self-assembled-monolayer functionalised electrodes
Adv. Mater., 2011, 23, 1447-1452.

We are very thankful for funding of our research activities in particular from the following institutions:

University of Basel
NCCR of the SNF