Unusual behavior of silicon oligomers and polymers having functional groups

Synthesis, structures, and electronic properties of silicon polymers and oligomers having hypervalent silicon moieties, polar substituents, or transition metal moieties are reported. UV spectra of pentacoordinate silicon oligomers reveal that the introduction of pentacoordinate silicon moieties into oligosilanes leads to a drastic change of the sigma(SiSi) --> sigma*(SiSi) excitation energies. Si-29-NMR spectra have proved that the conformation of pentacoordinate oligosilanes is tightly locked, indicating that free rotation about the Si-Si single bonds is nearly completely inhibited by electrostatic interaction. UV-vis spectra of polysilanes substituted with (alkoxycarbonyl)methyl groups exhibit unusual spectral properties such as long-wavelength absorption above 400 nm, and temperature- or solvent-dependent change of the UV spectra. Effective electron delocalization in Si-Ru-Ru-Si-C6H4 polymers was demonstrated by the absorption spectra. Solvent-sensitive skeletal rearrangement of the Si-Ru-Ru-Si moieties gives rise to a remarkable change of the optical properties of the polymers. (C) 2003 Elsevier B.V. All rights reserved.