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 language | English |
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Article number | 064502 |
Journal | Structural Dynamics |
Volume | 6 |
Issue number | 6 |
DOIs | |
Publication status | Published - 2019 Nov 1 |
Bibliographical note
Publisher Copyright:© 2019 Author(s).
ASJC Scopus subject areas
- Radiation
- Instrumentation
- Condensed Matter Physics
- Spectroscopy