Electronic structures of halogenated polysilanes

The electronic structures of halogenated polysilanes (PSi), whose side chains are replaced by halogen (X) atoms, have been theoretically investigated based on the first-principles calculations. It was found that non-bonding (n) electrons localizing at the X atom produce an important orbital mixing with the σ valence electrons delocalized in the direction of the PSi skeleton (σ-n mixing). This σ-n mixing splits the top of the valence bands, and creates unoccupied states in the band gap. This valence-band-splitting effectively narrows the band gap to the visible range, and the unoccupied state in the band gap has the potential to be an electron acceptor. Moreover, we also investigated several replacement patterns as well as the kind of replaced halogen species (X=F, Cl, Br, I). The dispersion and energy position of the unoccupied state(s) can be artificially tuned by these chemical modifications. Thus, halogenation can change PSi into optoelectronic polymers with visible photoluminescence.