Photoconductivity and electroabsorption in conjugated polymers

This dissertation presents the results of transient (subnonosecond) photoconductivity and electroabsorption spectroscopy of a variety of organic conjugated polymers. Although these two techniques may initially appear unrelated they actually probe many of the same quantities. In particular it will be shown that both techniques can provide information regarding the intrinsic anisotropy of quasi-one-dimensional polymeric systems. In addition, both experiments provide a sensitive measure of sample quality.; Transient photoconductivity measurements performed on oriented trans-polyacetylene prepaired by the Naarmann-Theophilou synthesis, which results in samples containing a relatively low defect content, show a large long-lived, temperature-dependent photocurrent not seen in trans-polyacetylene prepaired by other synthesis methods. By a comparison of the data to that obtained from high-quality single crystals of polydiacetylene, it is concluded that this long lived photocurrent implies a higher-quality polyacetylene. The anisotropic behavior for different polarizations of the incident light is presented together with the effect of light intensity, temperature and external field strength.; The results of spectroscopy and transient photoconductivity measurements on polyaniline in the fully reduced ("leucoemeraldine") and in the emeraldine base form are reported. A relatively strong photoconductive response is observed from pumping at 3.7 eV into the {dollar}pi{dollar} {dollar}-{dollar} {dollar}pisp{lcub}*{rcub}{dollar} absorption of leucoemeraldine, and a smaller photocurrent from pumping (at 1.9 eV and 3.7 eV) into the absorptions which characterize the emeraldine base. The results are interpreted in terms of the one-dimensional band structures calculated for the two forms of polyaniline.; Electroabsorption measurements are presented for unoriented cis and trans-polyacetylene and for oriented trans-polyacetylene. The electroabsorption spectrum of the unoriented material consists of a series of field induced absorptions and bleachings occurring at the band edge. In oriented trans-polyacetylene with the electric field parallel to the chain axis, the strongest of these features, which is often observed as a "knee" near 1.5 eV in the absorption spectrum, is highly suppressed, while the induced absorption at 1.28 eV is enhanced relative to the unoriented case. No electroabsorption signal is present when the external field is applied perpendicular to the chain direction. The dependence of the electroabsorption spectrum on temperature, electric field strength, incident light polarization and intensity is also described. An interpretation of the electroabsorption spectrum as electric field broadened, excited state phonon modes, is discussed.