Conformational analysis of trimethylsilyl-substituted trans-stilbenes: modeling of torsions in silicon-containing poly(para-phenylenevinylene)

Conformational analysis was carried out on trimethylsilyl (TMS)-substituted trans-stilbenes which were taken as models of silyl-substituted poly(para-phenylenevinylene). The bulky substituents at ortho positions increase the energy barrier towards the co-planar conformation which contributes to larger band gaps of the corresponding polymers. When two TMS groups exist at the ortho positions, the steric interaction between them plays an important role in the ring torsions. This effect increases the energy barrier towards the perpendicular conformation and consequently reduces the flexibility of the molecules. It was found that torsion analysis can lead to better understanding of various unique properties of silyl-substituted PPVs.