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Research

Supramolecular Chemistry

The main focus of our work is the development of functional supramolecular systems and we are especially interested in the following subjects:

Many projects in our group focus on the formation and characterization of self-assembled metallosupramolecular aggregates and template effects associated with these. Within the area of self-assembly of discrete oligonuclear metal coordination compounds we are especially interested in the stereoselectivity of these processes. Therefore, we have extensively studied the diastereoselective self-assembly of helicates and recently started to carry this approach forward to further oligonuclear 2D- and 3D-architectures. Thereby became very much interested in the self-assembly of multicomponent systems and especially in stereoselective self-sorting processes. In this way we are able to achieve the assembly of chiral aggregates with stereochemically well-defined cavities which can even be furnished by endo- or exohedral functional groups that allow for an endo- or exo-functionalization in a well-defined confined environment. Another issue here is the use of (metallo)supramolecular principles to develop new spin-crossover complexes.

Besides self-assembly processes we are also interested in the development of supramolecular systems whose functions can be controlled by allosteric effects. Therefore, we synthesize molecular structures which contain binding sites for a given substrate and an additional binding site for a metal ion. Here, the metal ion acts as an effector, because binding of the metal ion causes a substantial conformational change of the receptor structure which causes a drastic change of its binding affinity towards the substrate. In other words we can turn the receptor’s function on and off.

Furthermore we are working on the development and evaluation of covalently and non-covalently assembled artificial receptors for the recognition of chiral molecules. Here, we are also interested in establishing analytical techniques like (ESI) mass spectrometry as a valuable tool to characterize stereoselective molecular recognition processes or isothermal titration calorimetry to elucidate enthalpy-entropy compensation phenomena. Together with colleagues from Mainz we also develop new sensors for various analytes like drugs, aromatics, or explosives on the basis of quartz-microbalances. 

Finally, we prepare bistable rotaxanes in which certain molecular motions can be induced upon exposure to an external stimulus.

Organic Synthesis

As organic chemists we devote most of our time to the multi-step synthesis of our target compounds. Doing so we often come to a point where we have to develop completely new methodologies or where we have to extend known procedures. In most cases we prepare carbo- or heterocyclic aromatic compounds. In recent years we have established a reasonable know-how in the area of palladium- or nickel-mediated cross- and homo-coupling reactions which we have used extensively to prepare functionalized building blocks like pyridines, carbazoles, pyrroles, thiophenes, 2,2‘-bipyridines, 2,2‘-dihydroxy-1,1‘-binaphthyls (BINOLs), derivatives of Tröger’s base, 9,9‘-spirobifluorenes, [2.2]paracyclophanes, tribenzotriquinacenes, resorcin[4]arenes, pyridin[4]arenes, calix[n]arenes, oligo-p-phenylenes, oligo-p-phenylenethynylenes, oligothiophenes, squaraines and other p-conjugated oligohetarenes in an efficient manner. However, we also use classical approaches for the construction of (hetero‑) cyclic systems or their subsequent functionalization on a virtually daily basis.

A second major issue is the synthesis, chiral resolution, and assignment of the absolute configuration of chiral, dissymmetric compounds BINOLs, Tröger’s bases, suitably substituted [2.2]paracyclophanes, 9,9’-spirobifluorenes, or tribenzotriquinacenes.

Another focus of our work is and continues to be the synthesis of highly functionalized macrocyclic compounds like calixarenes, resocinarenes, pyridinarenes, cyclodedextrins and similar cone-shaped molecules. Besides methods to achieve macrocyclisations we strive to develop efficient protocols to achieve a four- or eight-fold functionalisation.

Functional Materials 

We also develop new materials with interesting optical and optoelectonical properties. These materials result from the self-assembly of p-conjugated molecular building blocks. We have prepared a number of functionalized oligo-p-phenylenes and other p-conjugated oligomers and were able to demonstrate that these form nanofiber-like structures on suitable solid supports upon deposition from the vapour phase. These materials can show such interesting properties like wave-guiding but also non-linear optical properties like frequency doubling. As an exciting extension we have started to deposit our oligomers from solutions into porous templates in order to get nanostructured materials with different sizes and properties.

Some of these materials could also be used to fabricate functioning devices like organic light-emitting field-effect transistors (OLEFETs), organic phototransistors (OPTs), organic solar cells (OSCs), or photodetectors.

Cooperations

Prof. Dr. Christoph A. Schalley, FU Berlin

- mass spectrometric and NMR-spectroscopic characterisation of supramolecular systems

- molecular shuttles based on bistabile rotaxanes

Prof. Dr. Markus Albrecht, RWTH Aachen

- synthesis and characterisation of helicates

- synthesis and characterisation of large oligonuclear metallosupramolecular cages

Prof. Dr. Ulrich Lüning, University of Kiel

- allosteric receptors

- synthesis of functionalised 1,10-phenanthrolines

- synthesis and chiral resolution of concave bimacrocyclic N-heterocyclic carbenes

Prof. Dr. Katharina Al-Shamery, Dr. Rainer Koch, Priv.-Doz. Dr. Holger Borchert, Jun.-Prof. Dr. Manuela Schiek, Prof. Dr. Jürgen Parisi, Universität Oldenburg, Prof. Dr. Horst-Günter Rubahn, Prof. Dr. Frank Balzer, Jun.-Prof. Dr. Jakob Kjelstrup-Hansen, Syddansk University (Sonderborg, Denmark), Prof. Dr. Derck Schlettwein, University of Gießen, Prof. Dr. Alf Mews, Priv.-Doz. Dr. Tobias Kipp, University of Hamburg

- preparation, growth and properties of organic nanofibers from functionalised p-conjugated oligomers

- new materials for the fabrication of organic solar cells, chirooptical sensors and photodetectors

Prof. Dr. Barbara Kirchner, Prof. Dr. Stefan Grimme, Prof. Dr. Thomas Bredow, University of Bonn

- Theoretical studies on the conformational behaviour of substituted 2,2‘-bipyridines and the dynamics of these conformational changes

- theoretical simulation of the molecular recognition of chiral ammonium ions

- theoretical simulation of the thermodynamic stability of diastereomeric metallosupramolecular aggregates

- elucidation of the absolute configuration of dissymmetric compounds and oligonuclear metal coordination compounds

- theroretical studies on the spin states of iron(II) containing metallosupramolecular aggregates

Dr. Marianne Engeser, University of Bonn

- mass spectrometric characterization of supramolecular systems

Prof. Dr. Claude Piguet, University of Genf

- experimental studies on the mechanism and energetics of the self-assembly of oligonuclear helicates

Prof. Dr. Gerhard Bringmann, Dr. Torsten Bruhn, University of Würzburg

- elucidation of the absolute configuration of dissymmetric compounds and oligonuclear metal coordination compounds

- synthesis of atropisomeric derivatives of Tröger’s base

Prof. Dr. Frank Neese, Dr. Eckhard Bill, Max-Planck Institute for Chemical Energy Conversion, Mühlheim a.d. Ruhr

- elucidation of the absolute configuration of dissymmetric compounds and oligonuclear metal coordination compounds

- Mößbauer-spectroscopy of iron(II) spin-crossover complexes

Prof. Dr. Klaus Meerholz Universität Köln, Prof. Dr. Gary Hanan, Université de Montreal (Kanada)

- self-assembly of chromophore decorated oligonuclear metallosupramolecular

- synthesis of new ligands for photoredox catalysis

Dr. Detlef Schröder (†), Czech Academy of Science, Prag (Czech Republic)

- studies on CH-activation by 2,2‘-bipyridine metal complexes

Prof. Dr. Konrad Koszinowski, University of Göttingen

- mass spectrometric studies on the role of copper ions in Suzuki cross-coupling reactions of pyridylboronic acid esters

Prof. Dr. Kenneth Wärnmark, University of Lund (Sweden)

- synthesis and chiral resolution of Tröger’s base derivatives

Prof. Dr. Henning Hopf, Technical University of Braunschweig, Prof. Dr. Dietmar Kuck, University of Bielefeld

- synthesis and chiral resolution of tribenzotriquinacenes

Prof. Dr. Javier de Mendoza, ICIQ Tarragona (Spain)

- self-assembly ofoligonuclear metallosupramolecular cage compounds

Prof. Dr. Kari Rissanen, University of Jyväskylä (Finland)

- structural characterisation of metallosupramolecular aggregates

- synthesis and self-assembly of pyridin[4]arenes

Prof. Dr. Jochen Mattay, University of Bielefeld

- synthesis and self-assembly of pyridin[4]arenes

Prof. Dr. Siegfried R. Waldvogel, University of Mainz

- preparation and evaluation of new quartz microbalance sensor systems

Dr. Maaz Zuhayra, Dr. Ulf Lützen, University Hospital Kiel

- synthesis and application of [18F]-PET-tracers

Prof. Dr. Carsten Schmuck, University of Duisburg-Essen

- DLS-measurements on metallosupramolecular aggregates

Prof. Dr. A. Stephen K. Hashmi, University of Heidelberg

- development of new chiral ligands for stereoselective transition metal catalysis

Prof. Dr. Olav Schiemann, University of Bonn

- ESR-experiments on metallosupramolecular aggregates

Prof. Dr. Johannes Beck, University of Bonn

- magnetic behaviour of metallosupramolecular aggregates

Dr. Wilfried Assenmacher, University of Bonn

- TEM-experiments on metallosupramolecular aggregates

Prof.s Dr. Andreas Gansäuer, Dr. Jörn Piel (University of Bonn), Prof.s Dr. Rüdiger Beckhaus, Dr. Peter Köll, Dr. Jürgen O. Metzger, Dr. Jürgen Martens (University of Oldenburg), Prof. Dr. Henry Strasdeit (University of Hohenheim), Prof. Dr. Gerd Liebezeit (Terramare Research Center Wilhelmshaven), and Prof. Dr. Werner Uhl (Universities of Marburg and Münster)

- NMR-spectroscopic characterisation of (metal-)organic compounds

 

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