Spectroscopy and transient photoconductivity of partially crystalline polyaniline

The results of spectroscopy and transient-photoconductivity measurements are presented for polyaniline in the fully reduced form (leucoemeraldine) and in the emeraldine-base form. Results from partially crystalline films (cast from solution in sulfuric acid) and from amorphous films (cast from dimethylforamide) are compared. We observed a relatively strong photoconductive response from pumping at 3.7 eV into the π-π^* absorption of leucoemeraldine and a smaller photocurrent from pumping (at 1.9 and 3.7 eV) into the two absorptions which characterize the emeraldine base. The 3.7-eV photocurrent in leucoemeraldine is a factor of 4–8 larger than that from the similar ultraviolet absorption in the emeraldine base, and the two photocurrents show a similar dependence of biasing field (linear at low light levels and more complex at high light levels). The photocurrent in the emeraldine base from 3.7-eV pumping is a factor of 3–4 larger (per photon) than that from 1.9-eV pumping. The results are interpreted in terms of the one-dimensional band structures calculated for the two forms of polyaniline.