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Measuring Intermolecular Excited State Geometry for Favorable Singlet Fission in Tetracene
Daniel Vong1, Farahnaz Maleki2, Eric C Novak3
1Department of Materials Science and Engineering, University of California Davis, Davis, California 95616, United States.
The Journal of Physical Chemistry Letters
|January 25, 2024
Summary
Singlet fission (SF) efficiently converts one high-energy photon into two lower-energy triplet excitons. This study reveals how structural changes in tetracene molecules lower the energy barrier for SF, enhancing photovoltaic potential.
Area of Science:
- Photovoltaics
- Materials Science
- Physical Chemistry
Background:
- Singlet fission (SF) converts one singlet excited state into two triplet excited states.
- Acenes like tetracene and pentacene are key molecules for studying SF.
- High SF quantum efficiencies in tetracene, despite an endoergic process, pose a scientific question.
Purpose of the Study:
- Investigate the mechanism behind tetracene's high SF quantum efficiency.
- Understand the role of intermolecular structural relaxation in SF.
- Clarify how tetracene overcomes the energy barrier for SF.
Main Methods:
- Inelastic neutron scattering (INS) measurements on optically excited acenes.
- Utilizing two different excitation energies for optical excitation.
- Time-dependent density functional theory (TD-DFT) for computational analysis.
Main Results:
- INS spectra reveal intermolecular structural relaxation upon triplet state formation.
- TD-DFT simulations show excited-state geometry influences singlet and triplet energy levels.
- The energy barrier for SF in tetracene is reduced to within the thermal energy (kT).
Conclusions:
- Intermolecular structural relaxation is crucial for enabling SF in tetracene.
- Excited-state geometry significantly impacts the energetics of SF.
- This work provides insights into optimizing SF for enhanced photovoltaic devices.
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