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When liquid crystals with a metal center are "shaking hands"

08.03.2005 - (idw) Friedrich-Schiller-Universität Jena

Chemists at Jena University and the University of Colorado introduce new polymerizable metal-containing liquid crystals with unique properties in the journal "Advanced Materials" Jena (08.03.05) Without liquid crystals (LC's) our cell phones and notebook computers would not be possible, for these compounds keep our display screens flat and lightweight. Being a phase of matter whose order is intermediate between that of a liquid and that of a three-dimensionally organized crystal, LC's show special properties. For instance, by applying electric fields the molecular orientation and hence the optical properties of LC's can be controlled. In addition to the variety of interesting properties that LC's already display, chemists at the Jena University and the University of Colorado at Boulder have added new ones. First of all, they used LC's containing a metal center of palladium or nickel. The rod-shaped organic LC moieties thus have a potentially active metal center, enableing them to do additional things such as perform catalytic reactions. Furthermore, special groups were added to the ends of molecules which are able to interact if exposed to high temperatures. The new LC's therefore form cross-linked network polymers in which their usual order is "frozen". How this has been attained and what the special qualities of these new, polymerizable, metal-containing LC's also called metallomesogens are, the scientists describe for the first time in todays latest issue of the journal "Advanced Materials" (Adv. Mater. 2005, 17, 602).

"It was my main objective to synthesize well arranged polymers which are still catalytically active", reports Alexander Martin. The chemist at Jena University investigates the prerequisites for catalytic reactions, in which the catalyst does not dissolve in the reaction media but is solidly stationed.
"This is important in order to prevent a contamination of the final product by the catalyst", he explains. It was the goal of the young scientist from Jena to link these metal-containing LC's while still in in their liquid-crystalline state in order to establish precursors for catalytic active, and stable polymeric networks with structured surfaces.

In this process Alexander Martin faced a general problem. During the polymerization process, where the tails of the LC'sare forced to "hold on to each other", the catalytic centers were always degraded. The chemist from Jena found the solution during a scholarship, granted to him by the Studienstiftung des deutschen Volkes, in the laboratory of Prof. Dr. Douglas L. Gin at the University of Colorado in Boulder, CO (USA). There, the scientists work with polymerizable LC's with 1,3-diene tails, which can be linked in two ways: either through a reaction induced by radicals, or by thermal intermolecular cross-linking. Only the latter reaction was suitable for the sensitive metal-containing LC's from Jena, affording polymers with undamaged metal centers. This, Alexander Martin has worked out during his stay in Boulder. The result has been implemented in his PhD-thesis, that he has carried under the supervision of Prof. Dr. Wolfgang Weigand at Jena University.

By combining their competencies, the scientists from Boulder and Jena have been able to design and synthezise the first samples of a new kind of metal-containing LC-polymer, which shows characteristics of LC's, polymers, and catalytically active compounds at once. "With these new metal-containing LC compounds new materials can be synthesized", says Prof. Dr. Wolfgang Weigand. "This is promising preparatory work for ordered, solid-state designer catalysts with new characteristics", agrees his American colleague Prof. Douglas L. Gin. Further collaborative research with scientists from both universities has already started.


Contact:
Alexander Martin, Prof. Dr. Wolfgang Weigand
Institute for Anorganic and Analytical Chemistry at the Jena University
August-Bebel-Strasse 2, D-07743 Jena
Tel.: ++0049 (0)3641 / 948166
E-Mail: alexander.martin@uni-jena.de and c8wewo@uni-jena.de
Weitere Informationen: http://www.wiley-vch.de/publish/en/journals/alphabeticIndex/2089/
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