Organic and Macromolecular Chemistry
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Organic and Macromolecular Chemistry |
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| Introduction | |
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research interests of our group lie in the area of synthetic organic chemistry
and are directed towards the synthesis of structurally novel, mono- and
polydispers polymers and the creation of supramolecular assemblies. This
objective involves both design and synthesis of hitherto unknown monomers
and requires the use of a broad range of organic reactions as well as stoichiometric
and catalytic reactions with main group metal and transition metal compounds.
It further demands the development of polymerization strategies and methods
which fulfill the requirements of a good polymer synthesis: efficiency and
quantifyable control of structure. Besides the realization of perfect macromolecules,
elucidation of their structures is considered very important. Reliable structure/property-correlations
can be obtained only if the nature of defects and the amount to which they
are incorporated is known. Some of the specific projects delineated below
have the potential to be developed into the exciting direction of covalent
chemistry between individual molecules.
The techniques for characterization are solution and solid state high-field
NMR spectroscopy, GPC, VPO, membrane osmosis, static and dynamic light
scattering, electrochemistry, photophysical methods as well as the scanning
probe microscopies. Whenever appropriate these characterization methods
are applied in tight cooperations with physicochemists and physicists.
If the solubility of a given polymer is not sufficient, measures to increase
its solubility are taken. This is why flexible chains play an important
role in many projects. Some of the projects presently being followed in
our group are the following: |
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Suzuki Polycondensation |
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| Development of a new step-growth polymerization with formation of CC single bonds for the synthesis of (rigid-rod) polyarylenes. Aspects which will be explored in future comprise an evaluation of this reaction's sensitivity to steric demand and its potential to employ diiodo and dichloro monomers (instead of dibromo). |  |
| Hybridization of the dendrimer and the rigid-rod concept in order to obtain nanoocylinders with defined diameters as novel, e.g., amphiphilic constituents for giganto-micelles, -vesicles, -membranes, etc., and as charged nano objects (novel polyelectrolytes) for supramolecular constructions with countercharged biological polyelectrolytes (like DNA). Development of a covalent chemistry between individualized such macromolecules while adsorbed in surface (in coop.). Generation of controlled hybrid structures of individualized dendronized poylmers with electrically conducting nanotubes, DNA, and alike. Generation of twodimensional model polymer networks, i.e., 10 net points between a few molecules of 500 nm lengths. Development of "cut and paste" type synthesis between individualized macromolecules while adsorbed on surface. |
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Functionalized Dendrimers with
covalently bound fluorescence markers |
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| This project aims at the synthesis of spherical dendrimers with generation-specifically attached fluorescent markers in order to probe the local polarity and to quantify a solvent-induced polarity gradient in dendrimers. Once such a gradient is proven and its orientation (from the interior to the exterior or the other way around) determined, these dendrimers should serve for light-induced, long-lived charge separations. |  |
| Functionalized
Dendrimers with anticancer drugs on surface |
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| Water soluble spherical dendrimers with cis-Pt-complexes in their periphery and their in-vitro and in-vivo testing are being developed in our group. Synthesis of dendrimers carrying either free propylamines, natural amino acids like L-methionine, L-phenylalanine,and L-aspartic acid, or ethylendiamine ligands leads to highly water-soluble structures, which can be examined in cell culture. Fluorescence markers (dansyl) are attached to the surface of the dendrimers and cellular uptake monitored by confocal fluorescence microscopy. In vitro toxicity of the synthesized dendrimers is being investigated to see whether they can be used as potential drug carriers. |  |
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| Development of maximum efficiency strategies for the synthesis of shape-persistent macrocycles with bipyridine and/or terpyridine units in the sides and corners, respectively. Study of their complexation behavior with various transition metals (like Ru, Os, Cu, Ag) under photophysical and nanoconstructions' aspects. Investigation of their self-assembly behavior in solution, bulk, and on surfaces. A main future goal is to try to develop a covalent chemistry between individualized such molecules while adsorbed on surface. Metal charged cycles on the nanometer scale will also be investigated as modules for the self-assembly into columnar aggregates in order to use them for the generation of ultrathin metal wires held in the confined geometry established by the cycles' stack. |  |
Beltshaped Macrocycles / Buckybelts |
| Development of Diels-Alder based strategies to the fully aromatic belt regions of fullerenes. Electrochemical and chemical characterization of these double-stranded, cyclic aromatics and their use in photochemically induced polymerization reactions. |  |
| Ladder polymers | |
| Ladder (ribbon) polymers consist of cyclic subunits that are connected to each other by two links that are attached to different sites of the respective subunits. Thus, ladder polymers have two independent strands of regularly tied bonds that do not merge into a single or double bond or cross each other like in a spiro connection. Since the mid-1980s much interest has existed in the non-linear optical and electrical properties of rigid-rod polymer films. High optical nonlinearities derived from p-conjugation, high laser-damage thresholds, and capability to form electrically conductive materials after doping suggested conjugated ladder polymers were potentially very interesting candidates for such applications. These characteristics led to a revival of interest in this class of polymers. |  |
| Modular chemistry | |
"In recent years, there has been increasing interest among chemists, physicists, materials scientists, biologists, engineers, and others in the assembly of well defined, relatively large functional structures from repetitive units that themselves are molecules of some complexity. Using the dictionary definition of a module (a detachable section, compartment, or unit with a specific purpose or function, and in electronics, a compact assembly functioning as a component of a larger unit), we feel that this newly emerging field of endeavor could be called "modular chemistry." Josef Michel, ed., Modular Chemistry, Kluwer Academic, 1995, pg. xiii. |
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| Important cooperation partners | ||
| Jürgen P. Rabe (SPM) |
Wolfgang Rettig (Fluorescence) |
Gerard van Koten (Catalysis) |
| Helmut Schlaad (GPC, LS) |
Stefan Förster (Neutron scattering) |
Jean-Pierre Majoral (Hybrid materials) |
| Vinvenco Balzani (Photophysics) |
Lothar Dunsch (Spectroelectrochemistry) | Ronald Gust (Pharmacy) |
| Manfred Schmidt (LS) |
Dieter Lentz (Single crystal X-ray diffraction) |
