DONOR AND ACCEPTOR STATES IN LIGHTLY DOPED POLYACETYLENE, (CH)X

The results of an experimental study of the infrared absorption of the (CH)x system, lightly doped (< 0.1%) with acceptors and donors, are presented. Additional absorptions are observed near 1370 cm-1 (width 50 cm-1) and 900 cm-1 (width 400 cm-1) upon doping with iodine, AsF5, and sodium. The two additional absorption maxima appear to be general features of lightly doped (CH)x independent of specific dopant or of cis (trans) content. Measurements on stretch-oriented films demonstrate that these absorption maxima are polarized primarily along the polymer chains. The narrow mode at 1370 cm-1 is attributed to a molecular vibration made ir active by the doping. The broader absorption centered at 900 cm-1 is discussed in terms of quasi-one-dimensional donor and acceptor bound states along the (CH)x chain. We include an experimental determination of the room-temperature dielectric constant in undoped (CH)x; 10-12, with uncertainty arising from the incomplete orientation of the (CH)x films. The bound-state energy is thus consistent with a one-dimensional hydrogenic model in which the Coulomb potential along the chain is reduced by Alternatively viewing semiconducting (CH)x as a Peierls distorted one-dimensional metal, we discuss localized domain-wall-like charged donor (acceptor) states induced by charge-transfer doping. © 1979 The American Physical Society.