Effect of organic vapors on the molecular conformation of non-doped polyaniline

A series of studies have been carried out on polyaniline (emeraldine base; EB) thin films deposited on glass substrates from aqueous solutions of polymerizing aniline (“in-situ” EB-I film). These films exhibit a Vis/UV spectrum in which the exciton peak has an absorption maximum at ~600 nm. Exposure of EB-I film to NMP vapor results in a red-shift of the exciton peak to ~650 nm (EB-II film). Doping of EB-II film by aq. HCl vapor gives a more delocalized electronic structure and higher electrical conductivity than those of the doped EB-I film. It is concluded that EB-I and EB-II exist in “tight coil” and “expanded coil” conformations respectively which do not change on doping in aqueous HCl.