Pressure dependence of the luminescence and Raman modes in polyfluorene

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file viewed on (February 28, 2007)Includes bibliographical references.Vita.Thesis (Ph.D.) University of Missouri-Columbia 2006.Dissertations, Academic -- University of Missouri--Columbia -- Physics.I present a study of the optical properties of poly-para-phenylene and three different side-chain substituted polyfluorene polymers. I present an analysis of the Raman spectra under hydrostatic pressures for three oligo(para-phenylene) materials (p-terphenyl, 3P; p-quaterphenyl, 4P; and p-hexaphenyl, 6P) under hydrostatic pressure up to 80 kbar, with a focus on the 15-25 kbar region where the molecules are known to be forced into a more planar state. I present studies of the photoluminescence (PL) and Raman modes of polyfluorene (PF2/6) under hydrostatic pressures of 0-120 kbar at room temperature. The distinct PL with associated vibronics observed at atmospheric pressure blue shifts and changes dramatically around 20 kbar, above this pressure a broad peak at about 2.3 eV, associated with the keto defect, begins to dominate the PL. Raman modes observed are the 1417 cm-1 mode from the C-C stretch within the monomer, the 1342 cm-1 and 1290 cm-1 modes from phenyl rings connecting the monomer units, and the 1600 cm-1 modes from the intra-ring C-C stretch. All Raman modes analyzed shift to higher energies with pressure. Some of the phonon lines exhibit an antiresonance effect at higher pressures that is indicative of a high electron phonon interaction between the Raman phonons and the (real) PL transitions

Hydrostatic pressure dependence of the luminescence and Raman frequencies in polyfluorene

DOI: 10.1103/PhysRevB.68.115203 http://link.aps.org/doi/10.1103/PhysRevB.68.115203We present studies of the photoluminescence (PL), absorption, and Raman scattering spectra from poly[2,7-(9,9′-bis(2-ethylhexyl))fluorene] under hydrostatic pressures of 0-100 kbar at room temperature. The well-defined PL and associated vibronics that are observed at atmospheric pressure change dramatically around 20 kbar in the bulk sample and at around 35 kbar for the thin-film sample. Beyond these pressures the PL emission from the backbone is swamped by strong peaks due to aggregates and keto defects in the 2.1-2.6 eV region. The Raman peaks shift to higher energies and exhibit unexpected antiresonance line shapes at higher pressures, indicating a strong electron-phonon interaction.S.G. acknowledges the donors of the American Chemical Society Petroleum Research Fund No. 38193-B7! for partial support of this research. U.S. thanks SONY International Europe, Stuttgart, and the Deutsche Forschungsgemeinschaft (DFG) for financial support

Geometry-Dependent Electronic Properties of Highly Fluorescent Conjugated Molecules

URL:http://link.aps.org/doi/10.1103/PhysRevLett.85.2388 DOI:10.1103/PhysRevLett.85.2388We present a combined experimental/theoretical study of the electronic properties of conjugated para- phenylene type molecules under high pressure up to 80 kbar. Pressure is used as a tool to vary the molecular geometry and intermolecular interaction. The influence of the latter two on singlet and triplet excitons as well as polarons is monitored via optical spectroscopy. We have performed band structure calculations for the planar poly(para-phenylene) and calculated the dielectric function. By varying the intermolecular distances and the length of the polymer repeat unit the observed pressure effects can be explained.Supported by the University of Missouri Research Board, OeNB Project No. 6608, the vector-computer facilities at the University of Graz

Functional Magnetic Resonance Imaging: Data Acquisition and Analysis

Provides information relevant to the conduct and interpretation of human brain mapping studies. Provides in-depth coverage of the physics of image formation, mechanisms of image contrast, and the physiological basis for image signals. Parenchymal and cerebrovascular neuroanatomy and application of sophisticated structural analysis algorithms for segmentation and registration of functional data are discussed. Additional topics include fMRI experimental design including block design, event related and exploratory data analysis methods, and building and applying statistical models for fMRI data. Human subject issues including informed consent, institutional review board requirements and safety in the high field environment are also presented. Probability, linear algebra, differential equations, and introductory or college-level subjects in neurobiology, physiology, and physics is required