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Tuning Spin Dynamics in Crystalline Tetracene.
Sam L Bayliss1, Felix Kraffert1, Rui Wang2
1Berlin Joint EPR Lab, Fachbereich Physik , Freie Universität Berlin , D-14195 Berlin , Germany.
The Journal of Physical Chemistry Letters
|April 3, 2019
Summary
Singlet fission in tetracene crystals is temperature and morphology dependent. Cooling switches triplet generation pathways, impacting spin dynamics and dephasing times, crucial for understanding this process.
Area of Science:
- Materials Science
- Quantum Chemistry
- Solid-State Physics
Background:
- Tetracene is a model organic semiconductor.
- Singlet fission generates two triplet excitons from one singlet exciton, a key process for advanced photovoltaics.
- Understanding spin dynamics in singlet fission is crucial for optimizing energy conversion.
Purpose of the Study:
- To investigate the influence of temperature and crystal morphology on spin dynamics during singlet fission in tetracene.
- To elucidate the mechanisms governing triplet exciton generation and spin polarization.
- To determine the spin dephasing times of singlet fission-generated triplets.
Main Methods:
- Time-resolved electron spin resonance (TR-ESR) spectroscopy.
- Variable temperature measurements (300 K to 200 K).
- Analysis of transient spin polarization signals.
Main Results:
- A temperature-dependent switch between singlet fission and intersystem crossing pathways was observed upon cooling.
- Transient spin polarization inverted with temperature change, indicating altered triplet generation mechanisms.
- Singlet fission-generated triplets in tetracene crystals exhibited a spin dephasing time of ~40 ns at room temperature.
- This dephasing time is approximately 100 times shorter than that for triplets on isolated tetracene molecules.
Conclusions:
- Crystal morphology and temperature significantly impact spin dynamics in tetracene's singlet fission process.
- The observed spin polarization inversion highlights the competition between different exciton generation pathways.
- The short dephasing time of fission-generated triplets underscores the importance of intermolecular interactions and morphology in singlet fission efficiency.
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