72 Electronic Conjugation in Branched Oligosilanes

Wednesday, November 4, 2009: 10:30 AM
Angus (Camino Real Hotel)
Clemens Krempner , Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX
Brent Moore , Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX
Matthew MacLeod , Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO
Josef Michl , Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO
One of the most important properties of oligosilane compounds is their intense electronic absorption in the near UV region that provides a representative example of sigma-conjugated systems. Recent studies on discrete conformers of linear oligosilanes have revealed the anti-conformation (SiSiSiSi dihedral angle = 180°) to be most effective for the extension of sigma-conjugation in long chain oligosilanes.In branched oligosilanes the conformational arrangement and the number of silicon atoms in the longest linear segment are the principal factors determining the excitation energy of the first intense transition. While the electronic excitation energy of linear oligosilanes decreases rapidly with increasing chain length, for some branched species, the electronic excitation can either increase or decrease as branches are added.
To study the influence of branching and silicon backbone conformation on the extent of sigma-conjugation in branched systems, we have synthesized a series of model compounds, ranging from branched to cyclic penta and hexasilanes. This presentation will include an overview of our findings pertaining to synthetic methodology, spectroscopic investigation, crystal structure, conformational studies and theoretical calculations.