An ab initio study of geometries, polarizabilities, and rotation barriers of polyphenylsilane oligomers

MP2 optimizations with the 6-31G* basis set have been performed on Si3(C6H5)2H6 and Si3(C6H5)3H5. The resulting structural information has been employed in determinations of rotation barriers and static polarizabilities at the HF/3-21G* level. Potential energy profiles for rotation about the central Si–Si bond have been obtained for two structural isomers of Si4(C6H5)4H6. Trends in polarizabilities for isotactic and syndiotactic oligomers from N=4 to N=8 have been extrapolated to the infinite polymer limit and the results are consistent with calculations where N=10. Helical structures have been considered through calculations on the N=8 chain with varying dihedral angles in the Si backbone.