Coherent acoustic phonon dynamics in chiral copolymers

Mirko Scholz, Marius Morgenroth, Min Ju Cho, Dong Hoon Choi, Thomas Lenzer, Kawon Oum

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Coherent phonon oscillations in the UV-Vis transient absorption and circular dichroism response of two chiral polyfluorene-based copolymer thin films are investigated. A slow oscillation in the hundred picosecond regime indicates the propagation of a longitudinal acoustic phonon with a frequency in the gigahertz range through cholesteric films of PFPh and PFBT, which allow for the optical determination of the longitudinal sound velocity in these polymers, with values of (2550 ± 140) and (2490 ± 150) m s-1, respectively. The oscillation is induced by a strain wave, resulting in a pressure-induced periodic shift of the electronic absorption bands, as extracted from a Fourier analysis of the transient spectra. The acoustic phonon oscillation is also clearly detected in the transient circular dichroism (TrCD) response of PFPh, indicating a transient pressure-induced shift of the CD spectrum and possibly also phonon-induced chirality changes via pitch length modulation of the cholesteric helical polymer stack.

Original languageEnglish
Article number064502
JournalStructural Dynamics
Volume6
Issue number6
DOIs
Publication statusPublished - 2019 Nov 1

ASJC Scopus subject areas

  • Radiation
  • Instrumentation
  • Condensed Matter Physics
  • Spectroscopy

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