Hydrostatic pressure dependence of the luminescence and Raman frequencies in polyfluorene

We 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.