Bu Ali, E.M., Bertran, A., Moise, G. et al. (5 more authors) (2025) Intersystem crossing outcompetes triplet-pair separation from 1(TT) below 270 K in anthradithiophene films. Journal of the American Chemical Society. ISSN: 0002-7863
Abstract
Singlet fission (SF) and triplet-triplet annihilation (TTA) are processes which may be exploited to boost the efficiency of solar energy technology. Despite being studied since the late 1960s, the mechanism of singlet fission is still not fully understood. This is partly because the main technique used to study singlet fission, optical or visible/near-IR transient absorption spectroscopy, cannot distinguish between the strongly coupled triplet-pair state <sup>1</sup>(TT), weakly interacting triplet pairs (T..T), and independent triplet states T<sub>1</sub> + T<sub>1</sub>. To solve this problem, we combine transient optical spectroscopy performed as a function of magnetic field and transient electron spin resonance (ESR) spectroscopy to probe the different steps involved in the singlet fission mechanism. By using transient photoluminescence spectroscopy performed as a function of magnetic field to selectively probe the second step of singlet fission: <sup>1</sup>(TT) ⇌ (T..T), we show that in a well-studied model system, anthradithiophene (diF-TES-ADT), this step is highly temperature-dependent, even though the first step, <sup>1</sup>S → <sup>1</sup>(TT), is not. Transient ESR measurements confirm the absence of singlet fission at temperatures between 40 and 250 K for this system, with clear signatures of triplets generated by intersystem crossing and evidence for decay by triplet-triplet annihilation, further supported by magnetic field effect measurements. We conclude that in polycrystalline diF-TES-ADT, intersystem crossing outcompetes triplet hopping at temperatures below 270 K, enabling direct intersystem crossing from the bound triplet pair <sup>1</sup>(TT) to an independent triplet state T<sub>1</sub> localized on a single chromophore. The generated triplets can re-encounter and decay through triplet-triplet annihilation.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2025 The Authors. This publication is licensed under CC-BY 4.0 - https://creativecommons.org/licenses/by/4.0/ |
Keywords: | Energy levels; Magnetic properties; Nuclear fission; Polarization; Quantum mechanics |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > School of Mathematical and Physical Sciences |
Funding Information: | Funder Grant number ENGINEERING AND PHYSICAL SCIENCE RESEARCH COUNCIL EP/M028437/1 Engineering and Physical Sciences Research Council EP/R042802/1 Engineering and Physical Sciences Research Council EP/L022613/1 Engineering and Physical Sciences Research Council EP/T012455/1 Engineering and Physical Sciences Research Council EP/V034804/1 ENGINEERING AND PHYSICAL SCIENCE RESEARCH COUNCIL EP/V055127/1 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 06 Aug 2025 11:13 |
Last Modified: | 06 Aug 2025 11:13 |
Status: | Published online |
Publisher: | American Chemical Society (ACS) |
Refereed: | Yes |
Identification Number: | 10.1021/jacs.5c00001 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:230154 |