Electronic Absorption and Structural Properties of Poly(di- n-butysilane) Precipitated for Solution at Low Temperature.

The Si-backbone in crystalline poly(di-n-butysilane) (PDBS) has been shown to be a 7/3 helix, which is in marked contrast to the trans chain conformation of poly(di-n-hexylsilane) (PDHS). The electronic absorption properties of these two polymers are almost identical in solution, but are entirely different in the solid state. In this work, we show that a new, long-wavelength absorbing solid form of PDBS can be prepared by precipitating the polymer from dilute solution at low temperature. The structure of the new form is investigated using sup (29) Si NMR and X-ray diffraction. On the basis of NMR and UV absorption, we conclude that the new polymorph of PDBS is characterized by a trans conformation, although it contains substantial intra- and intermolecular crystallographic disorder, unlike PDHS.