Spatial Separation of Triplet Excitons Drives Endothermic Singlet Fission

Justin Johnson, Nadezhda Korovina, Christopher Chang

Research output: Contribution to journalArticlepeer-review

79 Scopus Citations

Abstract

Molecules that undergo singlet fission, converting singlet excitons into pairs of triplet excitons, have potential as photovoltaic materials. The possible advantages of endothermic singlet fission (enhanced use of photon energy and larger triplet energies for coupling with common absorbers) motivated us to assess the role of exciton delocalization in the activation of this process. Here we report the synthesis of a series of linear perylene oligomers that undergo endothermic singlet fission and have endothermicities in the range 5–10 kBT at room temperature in solution. We study these compounds using transient spectroscopy and modelling to unravel the singlet and triplet dynamics. We show that the minimal number of coupled chromophores needed to undergo endothermic singlet fission is three, which provides sufficient statistical space for triplet excitons to separate and avoid annihilation—and a subsequent fast return to the singlet state. Our data additionally suggest that torsional motion of chromophores about the molecular axis following triplet-pair separation contributes to the increase in entropy, thus lengthening the triplet lifetime in longer oligomers. [Figure not available: see fulltext.]

Original languageAmerican English
Pages (from-to)391-398
Number of pages8
JournalNature Chemistry
Volume12
Issue number4
DOIs
StatePublished - 2020

Bibliographical note

Publisher Copyright:
© 2020, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.

NREL Publication Number

  • NREL/JA-5900-72986

Keywords

  • dimers
  • excitons
  • oligomers
  • organic photovoltaic materials
  • perylene
  • singlet fission
  • solar-photochemistry
  • spectroscopy
  • triplet

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