σσ* Transition in anti,cisoid Alternating Oligosilanes: Clear-Cut Evidence for Suppression of Conjugation Effect by a cisoid Turn

On the basis of the UV absorption spectra of the anti,cisoid alternating oligosilanes, the first experimental clear-cut evidence was presented for the generally accepted idea that the sigma conjugation in polysilanes does not effectively extend through a tetrasilane fragment with a small dihedral angle such as a cisoid turn.