Tuning Singlet Fission in π-Bridge-π Chromophores
Journal of the American Chemical Society
American Chemical Society
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Kumarasamy, E., Sanders, S., Tayebjee, M., Asadpoordarvish, A., Hele, T., Fuemmeler, E., Pun, A., et al. (2017). Tuning Singlet Fission in π-Bridge-π Chromophores. Journal of the American Chemical Society, 139 (36), 12488-12494. https://doi.org/10.1021/jacs.7b05204
We have designed a series of pentacene dimers separated by homoconjugated or non-conjugated 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 non-conjugated 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 exciton through singlet fission. Together, these studies enable us to articulate the role of the conjugation motif in iSF.
L.M.C. acknowledges support from the Office of Naval Research Young Investigator Program (award N00014-15-1- 2532) and Cottrell Scholar Award. S.N.S., A.B.P., and B.C. thank the NSF for GRFP (DGE 11-44155). This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under contract no. DE-SC0012704. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. M.J.Y.T. acknowledges receipt of an ARENA Postdoctoral Fellowship and a Marie Sklodowska Individual Fellowship. D.R.M. acknowledges support from an Australian Research Council Future Fellowship (FT130100214) and through the ARC Centre of Excellence in Exciton Science (CE170100026). Single crystal X-ray diffraction was performed at the Shared Materials Characterization Laboratory at Columbia University. Use of the SMCL was made possible by funding from Columbia University. N.A. acknowledges support from the NSF CAREER (award no. CHE-1555205), NSF EAGER (award no. CHE-1546607), and a Sloan Foundation Research Fellowship. J.C.D. and G.D.S. acknowledge funding through the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy (award no. DESC0015429).
European Commission Horizon 2020 (H2020) Marie Sk?odowska-Curie actions (705113)
External DOI: https://doi.org/10.1021/jacs.7b05204
This record's URL: https://www.repository.cam.ac.uk/handle/1810/267769