(from left to right) Joseph B. Lambert, Dmitriy G. Ter-Martirosov, Eric W. Donnelly, Charlie Y.-H. Tsai, and Senthil A. Gurusamy-Thangavelu
Our research is aimed at synthesizing new classes of molecules with useful and interesting electronic, optical, conformational, and spectroscopic properties. Many, but not all, of these molecules contain main-group elements such as silicon, germanium, sulfur, and phosphorus.
We are constructing polysilanes with dendritic architectures. The polysilane backbone (-Si-Si-Si-) has low-lying s* orbitals that can permit electron delocalization much like that involving orbitals in polyenes. The dendritic architecture provides stable species with redundant polysilane pathways and with an exact molecular weight (not a distribution as in linear polymers). Dendritic molecules have a core (in this case a silicon atom) with branches that split into multiple branches up to n times for the nth generation. We have prepared several examples of this new class of molecules and currently are assembling larger chain lengths to permit greater delocalization.
We are studying the stabilization of positive charge by nonadjacent functionalities. When the functionality is one atom from a carbocation, the phenomenon (called the beta effect) has been found to be very large for electron donors such as silicon and tin. The principal mechanism of stabilization is thought to be hyperconjugation. We have prepared the first long-lived such species and characterized it by NMR. We now have discovered that even electron-withdrawing groups can stabilize positive charge, a seemingly contradictory phenomenon. We have found that b phosphonate, phosphine oxide, phosphine sulfide, and sulfonyl groups can hyperconjugate with carbocations.
We are designing molecules that self-assemble into a three-dimensional lattice in the solid. The molecules require hydrogen bonding or covalent bonding in a defined geometry. Using silicon or tin as a core, we are preparing molecules with a variety of bonding motifs.
Joseph B. Lambert
Clare Hamilton Hall Professor of Chemistry
Charles Deering McCormick Professor of Teaching Excellence 1999-2002.
THE DANCING DENDRIMER
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Last updated February 22, 2008