Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 139, Issue 36, Pages 12488-12494Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.7b05204
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Funding
- Office of Naval Research Young Investigator Program [N00014-15-1-2532]
- Cottrell Scholar Award
- U.S. DOE Office of Science Facility, at Brookhaven National Laboratory [DE-SC0012704]
- National Science Foundation [ACI-1548562]
- ARENA
- Marie Sklodowska Individual Fellowship
- Australian Research Council [FT130100214]
- ARC Centre of Excellence in Exciton Science [CE170100026]
- Columbia University
- NSF CAREER [CHE-1555205]
- NSF EAGER [CHE-1546607]
- Sloan Foundation
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy [DE-SC0015429]
- Australian Research Council [FT130100214] Funding Source: Australian Research Council
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1555205] Funding Source: National Science Foundation
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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 sigma bonds negligibly affects the orbital overlap within the pi-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.
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