Here, we analyze correlated-triplet-pair (TT) singlet-fission intermediates toward two-triplet separation (T...T) using spin-state-averaged density matrix renormalization group electronic-structure calculations. Specifically, we compare the triplet–triplet exchange (J) for tetracene dimers, bipentacene, a subunit of the benzodithiophene–thiophene dioxide polymer, and a carotenoid (neurosporene). Exchange-split energy gaps of J and 3J separate a singlet from a triplet and a singlet from a quintet, respectively. We draw two new insights: (a) the canonical tetracene singlet-fission unit cell supports precisely three low-lying TT intermediates with order-of-magnitude differences in J, and (b) the separable TT intermediate in carotenoids emanates from a pair of excitations to the second triplet state. Therefore, unlike with tetracenes, carotenoid fission requires above-gap excitations. In all cases, the distinguishability of the molecular triplets—that is, the extent of orbital overlap—determines the splitting within the spin manifold of TT states. Consequently, J represents a spectroscopic observable that distnguishes the resemblance between TT intermediates and the T...T product.
Taffet, Elliot J., et al. "Overlap-Driven Splitting of Triplet Pairs in Singlet Fission." Journal of the American Chemical Society, vol. 142, no. 47, Nov. 2020. https://doi.org/10.1021/jacs.0c09276
Taffet, Elliot J., Beljonne, David, & Scholes, Gregory D. (2020). Overlap-Driven Splitting of Triplet Pairs in Singlet Fission. Journal of the American Chemical Society, 142(47). https://doi.org/10.1021/jacs.0c09276
Taffet, Elliot J., Beljonne, David, and Scholes, Gregory D., "Overlap-Driven Splitting of Triplet Pairs in Singlet Fission," Journal of the American Chemical Society 142, no. 47 (2020), https://doi.org/10.1021/jacs.0c09276
@article{osti_1768800,
author = {Taffet, Elliot J. and Beljonne, David and Scholes, Gregory D.},
title = {Overlap-Driven Splitting of Triplet Pairs in Singlet Fission},
annote = {Here, we analyze correlated-triplet-pair (TT) singlet-fission intermediates toward two-triplet separation (T...T) using spin-state-averaged density matrix renormalization group electronic-structure calculations. Specifically, we compare the triplet–triplet exchange (J) for tetracene dimers, bipentacene, a subunit of the benzodithiophene–thiophene dioxide polymer, and a carotenoid (neurosporene). Exchange-split energy gaps of J and 3J separate a singlet from a triplet and a singlet from a quintet, respectively. We draw two new insights: (a) the canonical tetracene singlet-fission unit cell supports precisely three low-lying TT intermediates with order-of-magnitude differences in J, and (b) the separable TT intermediate in carotenoids emanates from a pair of excitations to the second triplet state. Therefore, unlike with tetracenes, carotenoid fission requires above-gap excitations. In all cases, the distinguishability of the molecular triplets—that is, the extent of orbital overlap—determines the splitting within the spin manifold of TT states. Consequently, J represents a spectroscopic observable that distnguishes the resemblance between TT intermediates and the T...T product.},
doi = {10.1021/jacs.0c09276},
url = {https://www.osti.gov/biblio/1768800},
journal = {Journal of the American Chemical Society},
issn = {ISSN 0002-7863},
number = {47},
volume = {142},
place = {United States},
publisher = {American Chemical Society (ACS)},
year = {2020},
month = {11}}