Anomalous optical and ESR properties of doped polydiethynylsilanes

The optical, transport, and ESR properties of 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. I2 doping induces a single absorption band at -1.05 eV in solutions and lightly doped films, but another at -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 ~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.