Anomalous optical and ESR properties of doped polydiethynylsilanes

The optical, transport, and ESR properties of some soluble conducting four-membered polydiethynylsilane heterocycles are described. The undoped one-dimensional gap is 2.0 eV in both films and solutions; no photoluminescence is observed. I{sub 2} doping induces a single absorption band at {similar to}1.05 eV in solutions and lightly doped films, but another at {similar to}0.55 eV in heavily doped films. Both are correlated with strong ir-active vibrations associated with known lines in Raman scattering. The doping-induced ESR of the solutions is linear in the 1.05-eV peak, but only {similar to}2% of the carriers yield an ESR, which is motionally narrowed. No light-induced ESR is detected. The results are discussed in relation to solitons, polarons, and bipolarons in a degenerate-ground-state system.