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Published on: April 4, 2016
Vibrational energy flow between modes by dynamic mode coupling in THIATS J-aggregates
Daisuke Hasegawa1, Kazuaki Nakata, Eiji Tokunaga
1Department of Physics, Faculty of Science, Tokyo University of Science , 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan.
Ultrafast spectroscopy revealed excited molecular vibrations in THIATS cyanine dye J-aggregates. Energy flows to a 1633 cm(-1) mode, with excited state lifetimes of 52 fs and 540 fs determined.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Materials Science
Background:
- Cyanine dyes, like THIATS, are crucial in various optical applications.
- Understanding their excited-state dynamics is key to optimizing their performance.
- J-aggregates exhibit unique photophysical properties due to strong intermolecular interactions.
Purpose of the Study:
- To investigate the excited molecular vibrations and energy flow in THIATS J-aggregates.
- To determine the lifetimes of excited electronic states and electronic dephasing time.
- To utilize ultrafast spectroscopy for probing ultrafast dynamics in cyanine dyes.
Main Methods:
- Sub-10 femtosecond (fs) pulse laser for ultrafast pump-probe spectroscopy.
- Time-resolved two-dimensional difference absorption (ΔA) spectroscopy.
- Fourier transform and spectrogram analysis for vibrational mode identification.
- Exponential fitting for lifetime and dephasing time determination.
Main Results:
- Observed vibrational modes at 285, 485, 555, 824, and 1633 cm(-1) in THIATS J-aggregates.
- Detected modulation of the 1633 cm(-1) mode frequency with delay time, indicating energy flow.
- Identified energy transfer from other modes to the 1633 cm(-1) mode via a ~50 cm(-1) mode.
- Determined average excited state lifetimes (τ1 = 52 ± 5 fs, τ2 = 540 ± 78 fs).
- Measured electronic dephasing time (T2(ele)) of 18.30 fs.
Conclusions:
- Ultrafast spectroscopy successfully detected excited molecular vibrations in THIATS J-aggregates.
- Energy flow dynamics within the J-aggregate were elucidated.
- Key photophysical parameters, including excited-state lifetimes and electronic dephasing time, were quantified.
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