Localization length scales of triplet excitons in singlet fission materials

Bayliss, Sam L.; Thorley, Karl J.; Anthony, John E.; Bouchiat, H.; Chepelianskii, A. D.

doi:10.1103/physrevb.92.115432

Cited by 17 publications

(28 citation statements)

References 44 publications

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“…Due to the zero-field splitting, the | m s | = 1 emissive T and absorptive T + transitions from the |0i state to the |±i Zeeman states do not coincide, and these transition peaks are separated in magnetic field by B = D/gµ B (Fig. 2c), where the D parameter agrees with previous cw studies 15,24 . Selective population of the m s = 0 state through fission can be understood as follows.…”

Section: Spin Resonance Of Weakly Coupled Triplet Pairssupporting

confidence: 88%

“…Tetracene is a canonical singlet fission system that has been studied extensively for both its spin and electronic properties 11,12,22,23 . The modifications to tetracene not only make the material viable for scalable processing, but also change the crystal packing which in turn impacts electronic overlap in triplet pair geometries 24 . Its characterization via optical spectroscopy provides evidence for a distinct triplet-pair intermediate state 25 .…”

Section: Spin Resonance Of Weakly Coupled Triplet Pairsmentioning

confidence: 99%

“…Simulations were performed using a stochastic Liouville simulation (similar to Bayliss et al 24 ) for coupled triplet pairs. The ESR response as a function of magnetic field is found by solving the following master equation for the first-order ESR susceptibility:…”

Section: Spectral Simulationmentioning

confidence: 99%

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Strongly exchange-coupled triplet pairs in an organic semiconductor

et al. 2016

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From biological complexes to devices based on organic semiconductors, spin interactions play a key role in the function of molecular systems. For instance, triplet-pair reactions impact operation of organic light-emitting diodes as well as photovoltaic devices. Conventional models for triplet pairs assume they interact only weakly. Here, using electron spin resonance, we observe long-lived, strongly-interacting triplet pairs in an organic semiconductor, generated via singlet fission. Using coherent spin-manipulation of these two-triplet states, we identify exchange-coupled (spin-2) quintet complexes co-existing with weakly coupled (spin-1) triplets. We measure strongly coupled pairs with a lifetime approaching 3 µs and a spin coherence time approaching 1 µs, at 10 K. Our results pave the way for the utilization of high-spin systems in organic semiconductors. The dynamics of spin-dependent reactions impact organic systems across scales of complexity. In vivo radicalpair recombination has been implicated in the biological mechanism for avian navigation and in photosynthesis, while in organic semiconducting materials triplet spin-reactions can determine efficiencies in light-emitting diodes and photovoltaics 1-5. One such process, singlet fission, enables efficient production of two triplet excitons from an initially excited singlet state 6-8. This carrier multiplication process has enabled photovoltaic devices with over 100% external quantum efficiencies and holds promise as a means of harnessing the solar spectrum more efficiently 9,10. Fission proceeds from a photogenerated singlet exciton to an overall spin-zero triplet-pair state, conserving spin and enabling efficient triplet-pair formation. This initial pure singlet state can further decohere into the triplet-pair eigenstates, which we study here. Understanding how these triplet-pair states interact, annihilate, and move is critical for harnessing them in optoelectronic or spintronic applications. The fate of triplet pairs depends not only on their electronic degrees of freedom, but also on their spin properties, such as the pair spin coherence time. To date, spin dynamics of triplet pairs have predominantly been explored passively via photoluminescence experiments 11-13 , which do not allow for direct triplet-pair manipulation. Spin resonance techniques allow for active spin control but have previously been limited to continuous-wave (cw) studies of triplet pair-states 14,15 , although transient spin resonance has provided insight into triplet-transfer and triplet-charge interactions 16,17. Here we focus on the early-time behaviour of the non-equilibrium population of tripletpair states formed following singlet fission and before thermalization. We report the observation of exchange-coupled triplet pairs forming pure spin-quintet (total spin S = 2) states. Quintet states have been observed previously, for example in synthetic compounds that utilize directly bonded radical species 18 or in materials with degenerate ground state orbitals 19. Here we observe, i...

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Section: Spin Resonance Of Weakly Coupled Triplet Pairssupporting

confidence: 88%

Section: Spin Resonance Of Weakly Coupled Triplet Pairsmentioning

confidence: 99%

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Strongly exchange-coupled triplet pairs in an organic semiconductor

et al. 2016

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“…Figure 3a shows the TREPR spectra of TIPS-Ph-Tc obtained by 532-nm Nd:YAG laser excitations of frozen CH 2 Cl 2 solution (0.1 mM) at 77 K. Two pairs of peaks assigned to Q and T showing 15 and 50 mT splittings, respectively, were observed. The separation of T-peaks are consistent with the zerofield splitting (ZFS) of the excited triplet state of TIPS-Tc [24]. The splitting of the Q-peaks are similar to the splitting by the quintet state of the TIPS-Tc pair in thin films [19].…”

Section: Methodssupporting

confidence: 71%

Time-Resolved EPR Study on Singlet-Fission Induced Quintet Generation and Subsequent Triplet Dissociation in TIPS-Phenyl-Tetracene Aggregates

Nagashima

Kawaoka

Matsui

et al. 2018

J. Photopol. Sci. Technol.

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The singlet fission (SF) is expected to be powerful tool for exceeding the theoretical limit of the power conversion efficiency on the organic solar cells. However, little is known on the intermolecular SF mechanism in the solid state. In the present study, we have investigated intermolecular SF in 2-phenyl-6,11-bis(triisopropylsilylethynyl)tetracene (TIPS-Ph-Tc) in frozen solutions using a time-resolved electron paramagnetic resonance measurement at a low temperature. SF-born quintet states (Q) and subsequent dissociations into two triplet states (T + T) were detected for a diluted solute concentration of 10 -4 M in dichloromethane. The microsecond triplet dissociation was found to occur due to the amorphous morphology in the frozen aggregate, suggesting that Q is generated as a trapped state. Furthermore, it was also suggested that the T + T dissociation follows the Q generation due to a T-T repulsion, whose energy were determined by the negative exchange couplings in the triplet pairs, (TT).

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“…A natural explanation is the different molecular configurations accessible in TIPS-tetracene in which there are four rotationally inequivalent molecules in the crystal unit cell ( Fig. 2B ) [24]. Multiple triplet pairs may therefore be supported.…”

Section: Spectrally Resolving Interacting Tripletsmentioning

confidence: 99%

Site-selective measurement of coupled spin pairs in an organic semiconductor

Bayliss

Weiss

Mitioglu

et al. 2018

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

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From organic electronics to biological systems, understanding the role of intermolecular interactions between spin pairs is a key challenge. Here we show how such pairs can be selectively addressed with combined spin and optical sensitivity. We demonstrate this for bound pairs of spin-triplet excitations formed by singlet fission, with direct applicability across a wide range of synthetic and biological systems. We show that the site sensitivity of exchange coupling allows distinct triplet pairs to be resonantly addressed at different magnetic fields, tuning them between optically bright singlet ([Formula: see text]) and dark triplet quintet ([Formula: see text]) configurations: This induces narrow holes in a broad optical emission spectrum, uncovering exchange-specific luminescence. Using fields up to 60 T, we identify three distinct triplet-pair sites, with exchange couplings varying over an order of magnitude (0.3-5 meV), each with its own luminescence spectrum, coexisting in a single material. Our results reveal how site selectivity can be achieved for organic spin pairs in a broad range of systems.

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Localization length scales of triplet excitons in singlet fission materials

Cited by 17 publications

References 44 publications

Strongly exchange-coupled triplet pairs in an organic semiconductor

Strongly exchange-coupled triplet pairs in an organic semiconductor

Time-Resolved EPR Study on Singlet-Fission Induced Quintet Generation and Subsequent Triplet Dissociation in TIPS-Phenyl-Tetracene Aggregates

Site-selective measurement of coupled spin pairs in an organic semiconductor

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