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