Spectroscopic Approach to Energetics of Exciton Fission and Fusion in Tetracene Crystals

Tomkiewicz, Y.; Groff, R.P.; Avakian, P.

doi:10.1063/1.1674702

Cited by 164 publications

(164 citation statements)

References 29 publications

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“…According to our calculation, 4 is the smallest acene that satisfies the E(S 1 ) > 2E(T 1 ) condition. This also agrees with experiments that the singlet fission observed in 4 and 5 does not need much energy activation (29,111). The second condition is E(T 2 ) > 2E(T 1 ).…”

Section: St Energy Gapsupporting

confidence: 77%

Nature of ground and electronic excited states of higher acenes

Yang

Davidson

Yang

2016

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

174

208

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Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particleparticle random-phase approximation calculation. The 1 A g ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state 3 B 2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state 1 B 2u is a zwitterionic state to the short axis. The excited 1 A g state gradually switches from a doubleexcitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the 1 B 2u and excited 1 A g states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved.higher acenes | diradical | double excitation | particle-particle random-phase approximation | charge-transfer excitation

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Section: St Energy Gapsupporting

confidence: 77%

Nature of ground and electronic excited states of higher acenes

Yang

Davidson

Yang

2016

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

174

208

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“…The combined experimental data set comprising frequencies from Vodehnal and Stepan [46], Griffiths and Freedman [47] and Tomkiewicz et al [48] includes only 63 of the anticipated 84 frequencies and it is not possible to represent the heat capacity with so few frequencies using the method proposed. A second set of frequencies, a combination of computational planar frequencies of naphthacene, presented by Ohno [49] and out-of-plane frequencies from Cyvin et al Fig.…”

Section: Naphthacenementioning

confidence: 99%

Heat capacity prediction for polynuclear aromatic solids using vibration spectra

Sallamie

Shaw

2005

Fluid Phase Equilibria

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“…Whereas singlet fission in pentacene is exothermic by ∼100 meV (1), in tetracene it is found to be endothermic by ∼180 meV (1,(19)(20)(21). Accordingly, triplet formation is significantly faster in pentacene films (∼80 fs) (5) than in tetracene (∼90 ps) (22), although curiously in the latter material the process remains highly efficient and fully independent of temperature (22,23).…”

mentioning

confidence: 99%

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.

194

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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Spectroscopic Approach to Energetics of Exciton Fission and Fusion in Tetracene Crystals

Cited by 164 publications

References 29 publications

Nature of ground and electronic excited states of higher acenes

Nature of ground and electronic excited states of higher acenes

Heat capacity prediction for polynuclear aromatic solids using vibration spectra

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

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