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

5 Citations (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

Bibliographical note

Funding Information:
We are very thankful to T. Staedler, Y. Guo, and J. Fan (Institute of Materials Engineering, University of Siegen) for carrying out the AFM measurements on the thin films. Financial support for K.O. and T.L. was provided by the Deutsche Forschungsgemeinschaft (DFG) through Grant Nos. OU 58/11-1 and LE 926/12-1. D.H.C. and M.J.C. are thankful to the National Research Foundation of Korea (NRF) for the support through research Grant No. NRF 2019R1A6A1A11044070.

Publisher Copyright:
© 2019 Author(s).

ASJC Scopus subject areas

  • Radiation
  • Instrumentation
  • Condensed Matter Physics
  • Spectroscopy

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