Vapor phase "secondary doping" of polyaniline

A dramatic change occurs in the electronic spectrum of a thin (solid) film of polyaniline doped with the "primary dopant," d,l-camphorsulfonic acid (spun from its solution in chloroform on to a quartz plate) when it is exposed to the vapor of the "secondary dopant" m-cresol, at room temperature. The resistance decreases by a factor of > 10² and it becomes insoluble in chloroform due to an increase in its crystallinity. The localized polaron absorption at 780 nm is replaced by a very intense free carrier tail commencing at ≈ 1000 nm and increasing steadily in intensity to ≈ 2600 nm, which is consistent with delocalized electrons in the polaron band. "Secondary doping" with a variety of substituted phenols and a number of different "primary" protonic acid dopants is observed.