Properties of Doped Polyacetylene, (Ch)x

Linear polyacetylene, (CH)x is one of the simplest conjugated organic polymers, and it therefore has attracted the attention of polymer chemists and physicists for some time [1]. Each carbon atom is a bonded to one hydrogen and two neighboring carbon atoms consistent with sp2 hybridization. The II electrons delocalize into the bands in which carrier transport can occur. In the absence of bond alternation and Coulomb correlation the trans form of (CH)x would be a metal. In actuality the trans form of (CH)x has bond alternation and is thus a semiconductor. In a recent series of studies Shirakawa and coworkers [2,3,4] have succeeded in synthesizing polycrystalline films of (CH)x and have chemically doped these films with a variety of donors and acceptors to give n-type or p-type semiconductors. Transport and far IR transmission studies as a function of doping suggest that a semiconductor to metal transition occurs near 1 atomic % dopant concentration [3].