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Title: Tuning Singlet Fission in π-Bridge-π Chromophores

For this study, we have designed a series of pentacene dimers separated by homoconjugated or nonconjugated bridges that exhibit fast and efficient intramolecular singlet exciton fission (iSF). These materials are distinctive among reported iSF compounds because they exist in the unexplored regime of close spatial proximity but weak electronic coupling between the singlet exciton and triplet pair states. Using transient absorption spectroscopy to investigate photophysics in these molecules, we find that homoconjugated dimers display desirable excited-state dynamics, with significantly reduced recombination rates as compared to conjugated dimers with similar singlet fission rates. In addition, unlike conjugated dimers, the time constants for singlet fission are relatively insensitive to the interplanar angle between chromophores, since rotation about σ bonds negligibly affects the orbital overlap within the π-bonding network. In the nonconjugated dimer, where the iSF occurs with a time constant >10 ns, comparable to the fluorescence lifetime, we used electron spin resonance spectroscopy to unequivocally establish the formation of triplet–triplet multiexcitons and uncoupled triplet excitons through singlet fission. Together, these studies enable us to articulate the role of the conjugation motif in iSF.
Authors:
ORCiD logo [1] ; ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [1] ;  [1] ;  [1] ;  [1] ;  [6] ;  [1] ; ORCiD logo [6] ;  [1] ;  [5] ;  [3] ; ORCiD logo [7] ; ORCiD logo [1]
  1. Columbia Univ., New York, NY (United States). Department of Chemistry
  2. University of New South Wales, Sydney (Australia). School of Photovoltaic and Renewable Energy Engineering; University of Cambridge (United Kingdom). Cavendish Laboratory
  3. University of New South Wales, Sydney (Australia). ARC Centre of Excellence in Exciton Science, School of Physics
  4. Cornell Univ., Ithaca, NY (United States). Department of Chemistry and Chemical Biology; Cambridge University (United Kingdom). Jesus College
  5. Cornell Univ., Ithaca, NY (United States). Department of Chemistry and Chemical Biology
  6. Princeton Univ., NJ (United States). Department of Chemistry
  7. Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials
Publication Date:
Report Number(s):
BNL-114743-2017-JA
Journal ID: ISSN 0002-7863; KC0403020; TRN: US1800601
Grant/Contract Number:
SC0012704; SC0015429
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 36; Journal ID: ISSN 0002-7863
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), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Singlet Fission; Homoconjugated Dimers; Non-Conjugated; Organic Electronics; Pentacene Dimers; Electron Spin Resonance; Center for Functional Nanomaterials
OSTI Identifier:
1413948