Electroabsorption spectroscopy of conjugated polymers and carbon fullerenes and conjugated-polymer light-emitting devices.

摘要

The subject of this dissertation is the optical absorption and electroabsorption properties of conjugated polymers and carbon fullerenes. The experimental work was extended for polymers to include the manufacture and characterization of light-emitting devices.; The absorption and electroabsorption spectra for polymers are difficult to reconcile. Absorption spectra tend to be broad and featureless, and electroabsorption spectra display sharp features, some of which do not correspond to any features in absorption. A key issue is the reconciliation of these disparate results.; The conjugated polymers have quasi-one-dimensional chemical structures. Theoretical studies suggest that the optical transitions in these polymers are dominated by highly-correlated electronic states, as opposed to free-electron-like band states which characterize conventional semiconductors: however, the true nature of the electronic structure is disputed, and can be characterized as a "contest" between a band picture and an exciton description. This research applied absorption and electroabsorption spectroscopy techniques that produced evidence in support of highly-correlated exciton states: specifically, an electronic structure described by even- and odd-parity exciton states with binding energies greater than 0.5 eV. Direct evidence of a continuum band was not found in the experiments, which were designed to probe the subgap region; however, the experiments are shown to be consistent with theories that invoke strong electron correlation and predict the existence of a high-energy continuum band. In addition, a tenable mechanism based on a combination of derivative lineshape analysis and polymer chain-length distribution was developed to reconcile the disparate nature of the absorption and electroabsorption spectra.; Carbon fullerenes are an interesting and newly discovered form of carbon. The fullerenes and polymers have peculiar similarities and yet are optically, mechanically, and electrically distinct. The same techniques of absorption and electroabsorption spectroscopy were applied to two common fullerenes (C{dollar}sb{lcub}60{rcub}{dollar} and C{dollar}sb{lcub}70{rcub}{dollar}). It is believed that this work was the first such result established for C{dollar}sb{lcub}60{rcub}{dollar}. The results suggest that charge-transfer mechanisms are important in the spectroscopy of the visible optical region.; Finally, the optical properties of polymer light-emitting devices were investigated. A unique electrical symmetry of operation was established and investigated. A theory to explain this unusual mode of operation will be discussed.