Angewandte
Communications
Chemie
GRFP (grant number 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 number DE-SC0012704.
We are grateful to the Nuckolls lab for use of their UV/Vis
spectrophotometer.
Keywords: conjugated materials · heterodimers ·
organic electronics · photophysics · singlet fission
How to cite: Angew. Chem. Int. Ed. 2016, 55, 3373–3377
Angew. Chem. 2016, 128, 3434–3438
´
d) I. Paci, J. C. Johnson, X. Chen, G. Rana, D. Popovic, D. E.
Thompson, E. Hontz, S. R. Yost, P. D. Reusswig, M. E. Bahlke,
337; f) J. Lee, P. Jadhav, P. D. Reusswig, S. R. Yost, N. J.
Thompson, D. N. Congreve, E. Hontz, T. Van Voorhis, M. A.
Figure 3. Rise and decay kinetic traces of the triplet pair in PH, BP,
and PT, probed at the lmax of the triplet excited state absorption
spectra (683, 712, and 707 nm, respectively).
dependence on overall triplet pair energy. The lifetime of the
triplet pair decreases following the trend, PT> BP > PH, in
agreement with the trend of decreasing energy of the triplet
state (Figure 3). The triplet pair lifetime varies from 0.21 to
2.4 ns as the expected triplet pair energy decreases from
2.0 eV to 1.3 eV. In all cases, the radiative lifetime of the
triplet pair is much shorter than the radiative lifetime of the
monomers. Therefore, the decay in the directly linked acene
series is primarily non-radiative and can be explained by
invoking a simple energy gap argument for non-radiative
decay processes, where the rate of such a multiphonon process
is inversely proportionate to the number of phonons needed,
that is, the energy above the ground state.[9]
In summary, we have synthesized and characterized
a series of pentacene–oligoacene heterodimers. In PA, iSF
is significantly endothermic and does not occur. Instead, the
compound undergoes the slow singlet-state deactivation
processes of internal conversion, fluorescence, and a small
amount of ISC. However, in PT and PH, where iSF is
energetically feasible, iSF occurs with a 1 ps time constant, as
demonstrated by ultrafast transient absorption spectroscopy
and triplet photosensitization experiments. Triplet pair
recombination adheres to the energy gap law, but formation
of the triplet pair appears to be insensitive to the driving force
in iSF heterodimers. This study opens up a new possibility to
tune the excited-state dynamics of singlet fission in oligoa-
cenes. Additionally, these heterodimers offer a broadly appli-
cable strategy for creating iSF materials where energetics can
be tuned and spectrally resolved monomer transitions can be
exploited for detailed mechanistic studies of singlet fission.
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Acknowledgements
This work was funded by the Office of Naval Research Young
Investigator Program (grant number N00014-15-1-2532), ACS
Petroleum Research Fund, 3M Non-Tenured Faculty Award,
and Cottrell Scholar Award. S.N.S. and A.B.P. thank the NSF
3376
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 3373 –3377