Torsional potentials of simple polysilane derivatives

Abstract

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.

Direct Imprinting of Liquid Silicon

“…Polysilane is known to be very flexible owing to the much longer Si–Si bond compared with the C–C bond. Indeed, we calculated the barrier between the all-trans and all-gauche conformations in the structure of n -Si 4 H 10 to be only 1.2 kcal/mol, which agrees well with the value of 0.9 kcal/mol determined using an ab initio approach . The influence of this flexibility on the peak position was checked in Figure b, wherein the vibrational modes were calculated as a function of dihedral angle θ.…”

Effect of lamp cycling on conversion and stress development in ultraviolet‐cured acrylate coatings

“…The sensitivity of the optical and structural properties with respect to alkyl chain length is truly striking. Unsubstituted polysilane has a backbone torsion potential that gives rise to both anti and gauche conformations74, 75 in close analogy to saturated hydrocarbons. Dimethyl substitution creates significant steric packing constraints along the polymer backbone, and there are 10 to 15° deviations from planarity76, 77 that induce a hypsochromic shift in the optical interband absorption.…”

Vibrational and electronic second hyperpolarizabilities of all-trans polysilane chains

“…17 Force field, torsional potential and vibrational spectra of PSi and its oligomers have also been assigned. 18 All of these studies illustrate the attractive -conjugated character of PSi which is responsible for its thermochroïsm and photoluminescence a͒ Scientific Collaborator of the National Fund for Scientific Research ͑Bel-gium͒. b͒ Research Associate of the National Fund for Scientific Research ͑Bel-gium͒.…”