Striking the right balance of intermolecular coupling for high-efficiency singlet fission

Ryan D. Pensack, Andrew J. Tilley, Christopher Grieco, Geoffrey E. Purdum, Evgeny E. Ostroumov, Devin B. Granger, Daniel G. Oblinsky, Jacob C. Dean, Grayson S. Doucette, John B. Asbury, Yueh Lin Loo, Dwight S. Seferos, John E. Anthony, Gregory D. Scholes

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Singlet fission is a process that splits collective excitations, or excitons, into two with unity efficiency. This exciton splitting process, unique to molecular photophysics, has the potential to considerably improve the efficiency of optoelectronic devices through more efficient light harvesting. While the first step of singlet fission has been characterized in great detail, subsequent steps critical to achieving overall highly-efficient singlet-to-triplet conversion are only just beginning to become well understood. One of the most elementary suggestions, which has yet to be tested, is that an appropriately balanced coupling is necessary to ensure overall highly efficient singlet fission; that is, the coupling needs to be strong enough so that the first step is fast and efficient, yet weak enough to ensure the independent behavior of the resultant triplets. In this work, we show how high overall singlet-to-triplet conversion efficiencies can be achieved in singlet fission by ensuring that the triplets comprising the triplet pair behave as independently as possible. We show that side chain sterics govern local packing in amorphous pentacene derivative nanoparticles, and that this in turn controls both the rate at which triplet pairs form and the rate at which they decay. We show how compact side chains and stronger couplings promote a triplet pair that effectively couples to the ground state, whereas bulkier side chains promote a triplet pair that appears more like two independent and long-lived triplet excitations. Our results show that the triplet pair is not emissive, that its decay is best viewed as internal conversion rather than triplet-triplet annihilation, and perhaps most critically that, in contrast to a number of recent suggestions, the triplets comprising the initially formed triplet pair cannot be considered independently. This work represents a significant step toward better understanding intermediates in singlet fission, and how molecular packing and couplings govern overall triplet yields.

Original languageEnglish (US)
Pages (from-to)6240-6259
Number of pages20
JournalChemical Science
Volume9
Issue number29
DOIs
StatePublished - Jan 1 2018

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Optoelectronic devices
Ground state
Conversion efficiency
Nanoparticles
Derivatives
LDS 751
pentacene

All Science Journal Classification (ASJC) codes

  • Chemistry(all)

Cite this

Pensack, R. D., Tilley, A. J., Grieco, C., Purdum, G. E., Ostroumov, E. E., Granger, D. B., ... Scholes, G. D. (2018). Striking the right balance of intermolecular coupling for high-efficiency singlet fission. Chemical Science, 9(29), 6240-6259. https://doi.org/10.1039/c8sc00293b
Pensack, Ryan D. ; Tilley, Andrew J. ; Grieco, Christopher ; Purdum, Geoffrey E. ; Ostroumov, Evgeny E. ; Granger, Devin B. ; Oblinsky, Daniel G. ; Dean, Jacob C. ; Doucette, Grayson S. ; Asbury, John B. ; Loo, Yueh Lin ; Seferos, Dwight S. ; Anthony, John E. ; Scholes, Gregory D. / Striking the right balance of intermolecular coupling for high-efficiency singlet fission. In: Chemical Science. 2018 ; Vol. 9, No. 29. pp. 6240-6259.
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Pensack, RD, Tilley, AJ, Grieco, C, Purdum, GE, Ostroumov, EE, Granger, DB, Oblinsky, DG, Dean, JC, Doucette, GS, Asbury, JB, Loo, YL, Seferos, DS, Anthony, JE & Scholes, GD 2018, 'Striking the right balance of intermolecular coupling for high-efficiency singlet fission', Chemical Science, vol. 9, no. 29, pp. 6240-6259. https://doi.org/10.1039/c8sc00293b

Striking the right balance of intermolecular coupling for high-efficiency singlet fission. / Pensack, Ryan D.; Tilley, Andrew J.; Grieco, Christopher; Purdum, Geoffrey E.; Ostroumov, Evgeny E.; Granger, Devin B.; Oblinsky, Daniel G.; Dean, Jacob C.; Doucette, Grayson S.; Asbury, John B.; Loo, Yueh Lin; Seferos, Dwight S.; Anthony, John E.; Scholes, Gregory D.

In: Chemical Science, Vol. 9, No. 29, 01.01.2018, p. 6240-6259.

Research output: Contribution to journalArticle

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T1 - Striking the right balance of intermolecular coupling for high-efficiency singlet fission

AU - Pensack, Ryan D.

AU - Tilley, Andrew J.

AU - Grieco, Christopher

AU - Purdum, Geoffrey E.

AU - Ostroumov, Evgeny E.

AU - Granger, Devin B.

AU - Oblinsky, Daniel G.

AU - Dean, Jacob C.

AU - Doucette, Grayson S.

AU - Asbury, John B.

AU - Loo, Yueh Lin

AU - Seferos, Dwight S.

AU - Anthony, John E.

AU - Scholes, Gregory D.

PY - 2018/1/1

Y1 - 2018/1/1

N2 - Singlet fission is a process that splits collective excitations, or excitons, into two with unity efficiency. This exciton splitting process, unique to molecular photophysics, has the potential to considerably improve the efficiency of optoelectronic devices through more efficient light harvesting. While the first step of singlet fission has been characterized in great detail, subsequent steps critical to achieving overall highly-efficient singlet-to-triplet conversion are only just beginning to become well understood. One of the most elementary suggestions, which has yet to be tested, is that an appropriately balanced coupling is necessary to ensure overall highly efficient singlet fission; that is, the coupling needs to be strong enough so that the first step is fast and efficient, yet weak enough to ensure the independent behavior of the resultant triplets. In this work, we show how high overall singlet-to-triplet conversion efficiencies can be achieved in singlet fission by ensuring that the triplets comprising the triplet pair behave as independently as possible. We show that side chain sterics govern local packing in amorphous pentacene derivative nanoparticles, and that this in turn controls both the rate at which triplet pairs form and the rate at which they decay. We show how compact side chains and stronger couplings promote a triplet pair that effectively couples to the ground state, whereas bulkier side chains promote a triplet pair that appears more like two independent and long-lived triplet excitations. Our results show that the triplet pair is not emissive, that its decay is best viewed as internal conversion rather than triplet-triplet annihilation, and perhaps most critically that, in contrast to a number of recent suggestions, the triplets comprising the initially formed triplet pair cannot be considered independently. This work represents a significant step toward better understanding intermediates in singlet fission, and how molecular packing and couplings govern overall triplet yields.

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Pensack RD, Tilley AJ, Grieco C, Purdum GE, Ostroumov EE, Granger DB et al. Striking the right balance of intermolecular coupling for high-efficiency singlet fission. Chemical Science. 2018 Jan 1;9(29):6240-6259. https://doi.org/10.1039/c8sc00293b