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Title: A Direct Mechanism of Ultrafast Intramolecular Singlet Fission in Pentacene Dimers

Interest in materials that undergo singlet fission (SF) has been catalyzed by the potential to exceed the Shockley–Queisser limit of solar power conversion efficiency. In conventional materials, the mechanism of SF is an intermolecular process (xSF), which is mediated by charge transfer (CT) states and depends sensitively on crystal packing or molecular collisions. In contrast, recently reported covalently coupled pentacenes yield ~2 triplets per photon absorbed in individual molecules: the hallmark of intramolecular singlet fission (iSF). But, the mechanism of iSF is unclear. Here, using multireference electronic structure calculations and transient absorption spectroscopy, we establish that iSF can occur via a direct coupling mechanism that is independent of CT states. Moreover, we show that a near-degeneracy in electronic state energies induced by vibronic coupling to intramolecular modes of the covalent dimer allows for strong mixing between the correlated triplet pair state and the local excitonic state, despite weak direct coupling.
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [2] ;  [1]
  1. Cornell Univ., Ithaca, NY (United States)
  2. Columbia Univ., New York, NY (United States)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
OSTI Identifier:
1251272
Report Number(s):
BNL-112540-2016-JA
Journal ID: ISSN 2374-7943; R&D Project: 16063/16058; KC0403020
Grant/Contract Number:
SC00112704; SC0014563
Type:
Published Article
Journal Name:
ACS Central Science
Additional Journal Information:
Journal Volume: 2; Journal Issue: 5; Journal ID: ISSN 2374-7943
Publisher:
American Chemical Society (ACS)
Research Org:
Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Center for Functional Nanomaterials