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Coherent acoustic phonon dynamics in chiral copolymers.
- Source :
- Structural Dynamics; Nov2019, Vol. 6 Issue 6, p1-7, 7p
- Publication Year :
- 2019
-
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<superscript>−1</superscript>, 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. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 23297778
- Volume :
- 6
- Issue :
- 6
- Database :
- Complementary Index
- Journal :
- Structural Dynamics
- Publication Type :
- Academic Journal
- Accession number :
- 140975494
- Full Text :
- https://doi.org/10.1063/1.5124438