TORSIONAL POTENTIALS OF SIMPLE POLYSILANE DERIVATIVES

Torsional potential curves for simple infinite polysilane derivatives are calculated by various ab initio and semiempirical crystal orbital methods. The comparison includes polysilane, poly(difluorosilane), poly(methylsilane), poly(dimethylsilane), and poly(diethylsilane) and the two simplest carbon analogues polyethylene and poly(tetrafluoroethylene) as well as polygermane. Generally, the potential curves are more flat going from the carbon compounds to the silicon compounds. For polysilane the all-trans conformation is comparable or less stable in energy than the gauche conformation. The addition of bulkier side groups locks in the all-trans conformation relative to the gauche conformation. Connection of energetic with the thermochromic properties of polysilanes is discussed. A vibrational analysis and the corresponding phonon dispersion curves of polysilane with both all-trans and helical conformations are given for the first time. © 1990, American Chemical Society. All rights reserved.