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Published on: August 13, 2019
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Coherent acoustic phonon dynamics in chiral copolymers
Mirko Scholz1, Marius Morgenroth1, Min Ju Cho2
1Physical Chemistry, University of Siegen, Adolf-Reichwein-Str. 2, 57076 Siegen, Germany.
Structural Dynamics (Melville, N.Y.)
|January 2, 2020
Summary
Coherent phonon oscillations were observed in chiral polymer films using UV-Vis spectroscopy. This study determined the longitudinal sound velocity in these polymers, revealing insights into acoustic phonon propagation.
Area of Science:
- Materials Science
- Polymer Physics
- Spectroscopy
Background:
- Chiral polymers exhibit unique optical properties.
- Understanding phonon dynamics is crucial for advanced materials.
- Transient absorption and circular dichroism are sensitive probes of electronic and structural changes.
Purpose of the Study:
- To investigate coherent phonon oscillations in chiral polyfluorene-based copolymer thin films.
- To determine the longitudinal sound velocity in these polymer films.
- To explore the influence of acoustic phonons on optical and chiral properties.
Main Methods:
- UV-Vis transient absorption spectroscopy.
- Transient circular dichroism (TrCD) spectroscopy.
- Fourier analysis of transient spectra.
Main Results:
- Coherent phonon oscillations in the hundred picosecond regime were detected.
- Longitudinal acoustic phonon propagation was observed in cholesteric films (PFPh and PFBT).
- Longitudinal sound velocities were determined as (2550 ± 140) m s⁻¹ for PFPh and (2490 ± 150) m s⁻¹ for PFBT.
- Acoustic phonon oscillations were also observed in the TrCD response of PFPh.
Conclusions:
- The study successfully identified and characterized coherent acoustic phonon oscillations in chiral polymer films.
- The findings provide a method for optically determining longitudinal sound velocity in these materials.
- Phonon-induced strain affects electronic absorption bands and potentially modulates polymer chirality.
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