Singlet Fission: From Coherences to Kinetics

Piland, Geoffrey B.; Burdett, Jonathan J.; Dillon, Robert J.; Bardeen, Christopher J.

doi:10.1021/jz500676c

Cited by 134 publications

(166 citation statements)

References 49 publications

(76 reference statements)

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“…We can compare the results here with studies from films of tetracene, where the first step of highly efficient endothermic singlet fission is temperature independent (22,23) and has been proposed to involve barrier-free formation of an intermediate state (32,33) or tunnelling into a bound triplet pair (22). We find that our model is in qualitative agreement with these other studies; our endothermic system reveals rapid formation of a bound intermediate with triplet character that goes on to produce two free triplet excitons over a longer timescale.…”

Section: Resultsmentioning

confidence: 70%

Identification of a triplet pair intermediate in singlet exciton fission in solution

Stern

Musser

Gélinas

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

190

260

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Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley-Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spinsinglet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]-tetracene we find rapid (<100 ps) formation of excimers and a slower (∼10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process.T he fission of photogenerated spin-singlet excitons into pairs of spin-triplet excitons is an effective way to generate triplet excitons in organic materials (1, 2). Because the triplets produced are coupled into an overall singlet state, spin is conserved and triplet formation can proceed on sub-100-fs timescales (1, 3-5) with yields of up to 200% (1, 6, 7). Current interest in singlet fission is driven by its potential to improve the efficiency of solar cells by circumventing the Shockley-Queisser limit for single-junction devices (8-10). Incorporating singlet fission material within a lowband-gap solar cell should make it possible to capture the energy normally lost to thermalization following the absorption of highenergy photons (11,12). An external quantum efficiency of 129% (13) and an internal quantum efficiency of >180% (14) have been reported using pentacene as the singlet fission material and fullerene (C 60 ) as electron acceptor. Despite such significant advances, many questions remain about the underlying mechanism of triplet formation, such as the role of intermediate electronic states and the ability of systems to undergo endothermic fission.The basis of most kinetic descriptions of singlet fission is the triplet pair state 1 (TT), which is entangled into an overall singlet and is an essential intermediate for the formation of two free triplet excitons (1, 15). Whether this intermediate state is present only transiently, as expected in exothermic systems such as pentacene, or whether it can be sufficiently long lived to also play a central role in the fission process in slower systems is unclear. Transient absorption measurements of the canonical systems pentacene and tetracene in the solid state allow clear identification of only the singlet and triplet states (3,6,16,17), meaning the character of any intermediate has not been ob...

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Section: Resultsmentioning

confidence: 70%

Identification of a triplet pair intermediate in singlet exciton fission in solution

Stern

Musser

Gélinas

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

190

260

View full text Add to dashboard Cite

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“…The perfect agreement between the decays of 1 (TT)→S n and the 1 (T 1 T 1 )→ 1 (T 1 T n ) signals suggests that there are negligible transitions within the triplet pair manifold, for example, 1 (TT)→ 5 (TT) or 1 (TT)→ 3 (TT), during the lifetime (450 ps) of the triplet pair state. Transitions within the triplet pair manifold are expected to occur on much longer time scales ( 18 , 53 ). …”

Section: Resultsmentioning

confidence: 99%

Distinct properties of the triplet pair state from singlet fission

et al. 2017

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“…Bardeen and coworkers published a short review on molecular excitons including singlet fission (8) and a perspective on singlet fission mechanisms (9). Several accounts on the subject have also appeared recently in a special issue of Accounts of Chemical Research on multiexcitons edited by one of us (10), focusing on specific aspects of singlet fission, such as general design principles (11), electronic coherence (12), spin coherence (13), and firstprinciples analysis (14), as well as experimental measurements and applications to photovoltaics (15,16).…”

Section: Introductionmentioning

confidence: 99%

Charge Transfer–Mediated Singlet Fission

Monahan

Zhu

2015

Annu. Rev. Phys. Chem.

264

403

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Singlet fission, the splitting of a singlet exciton into two triplet excitons in molecular materials, is interesting not only as a model many-electron problem, but also as a process with potential applications in solar energy conversion. Here we discuss limitations of the conventional four-electron and molecular dimer model in describing singlet fission in crystalline organic semiconductors, such as pentacene and tetracene. We emphasize the need to consider electronic delocalization, which is responsible for the decisive role played by the Mott-Wannier exciton, also called the charge transfer (CT) exciton, in mediating singlet fission. At the strong electronic coupling limit, the initial excitation creates a quantum superposition of singlet, CT, and triplet-pair states, and we present experimental evidence for this interpretation. We also discuss the most recent attempts at translating this mechanistic understanding into design principles for CT state-mediated intramolecular singlet fission in oligomers and polymers.

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Singlet Fission: From Coherences to Kinetics

Cited by 134 publications

References 49 publications

Identification of a triplet pair intermediate in singlet exciton fission in solution

Identification of a triplet pair intermediate in singlet exciton fission in solution

Distinct properties of the triplet pair state from singlet fission

Charge Transfer–Mediated Singlet Fission

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