Optical properties of polysilanes with various silicon skeletons

In this account, I present a brief overview of the optical properties of polysilanes with various silicon skeletons reviewing previous studies and supplying new experimental results. The optical properties of branched polysilanes such as network polysilane (polysilyne), polysilane dendrimer, and organosilicon nanocluster (OSI) are discussed here. These polysilanes have higher dimensionalities in comparison with a linear polysilane that can be considered as a one-dimensional silicon. The optical properties of the polysilanes are remarkably influenced by the structure of the silicon skeleton. The emission spectra of branched polysilanes are characterized by the dual emission in the UV and visible regions and the large Stokes shift between the absorption and emission spectra. The dual emission was explained by a configuration coordinate model considering the emissions from the excited state of the linear Si–Si chain and a localized excited state of branching points. The localized excited state induced by the distortion of the Si–Si chain around the branching point was suggested. The time-resolved emission spectra of polysilane dendrimer show the energy migration from the linear Si–Si chain to the branching point. The quantum size effect also influences the optical properties of polysilanes. The optical energy gap of OSI decreased remarkably with increasing the size. Further decrease of the energy gap was observed by heat treatment of the OSI film, which was explained by the reconstruction of the Si skeleton accompanying the elimination of organic side chain.