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Ultra-fast intramolecular singlet fission to persistent multiexcitons by molecular design

Abstract

Singlet fission—that is, the generation of two triplets from a lone singlet state—has recently resurfaced as a promising process for the generation of multiexcitons in organic systems. Although advances in this area have led to the discovery of modular classes of chromophores, controlling the fate of the multiexciton states has been a major challenge; for example, promoting fast multiexciton generation while maintaining long triplet lifetimes. Unravelling the dynamical evolution of the spin- and energy conversion processes from the transition of singlet excitons to correlated triplet pairs and individual triplet excitons is necessary to design materials that are optimized for translational technologies. Here, we engineer molecules featuring a discrete energy gradient that promotes the migration of strongly coupled triplet pairs to a spatially separated, weakly coupled state that readily dissociates into free triplets. This ’energy cleft’ concept allows us to combine the amplification and migration processes within a single molecule, with rapid dissociation of tightly bound triplet pairs into individual triplets that exhibit lifetimes of ~20 µs.

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Fig. 1: Overview of iSF building blocks and design schemes.
Fig. 2: Dynamics of singlet fission and energy transfer.
Fig. 3: Time-resolved electron-spin resonance spectroscopy of the energy cleft materials.
Fig. 4: Effectiveness of design schemes for free-triplet generation.

Data availability

The data supporting the findings of this study are available in the paper and its Supplementary Information; further data are available from the corresponding author on reasonable request.

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Acknowledgements

L.M.C. acknowledges support from the Office of Naval Research Young Investigator Program (award no. N00014-15-1-2532) and a Cottrell Scholar Award. S.N.S. and A.B.P. thank the NSF for Graduate Research Fellowship Program (DGE 11-44155). S.N.S. acknowledges the NSF for receipt of a GROW award to perform work at UNSW. This research used resources of the Center for Functional Nanomaterials (which is a US DOE Office of Science Facility) at Brookhaven National Laboratory under contract no. DE-SC0012704. M.J.Y.T. acknowledges receipt of an ARENA Postdoctoral Fellowship and a Marie Sklodowska Curie Individual Fellowship (grant no. 705113). D.R.M. acknowledges support from an Australian Research Council Future Fellowship (grant no. FT130100214) and through the ARC Centre of Excellence in Exciton Science (grant no. CE170100026).

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Contributions

S.N.S., L.M.C. and M.Y.S. oversaw the project. A.B.P., S.N.S., E.K. and L.M.C. designed the molecules. S.N.S., D.N. and M.Y.S. carried out the transient absorption spectroscopy measurements and data analysis. A.B.P. and E.K. synthesized and characterized the molecules. A.A., M.J.Y.T. and S.N.S. carried out tr-ESR experiments and the data were also analysed by M.Y.S. and D.R.M. S.N.S., L.M.C. and M.Y.S. wrote the paper with contributions from all authors.

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Correspondence to Samuel N. Sanders or Luis M. Campos or Matthew Y. Sfeir.

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Competing interests

A.B.P., E.K., S.N.S., L.M.C. and M.Y.S. are named as inventors on a patent (WO 2016/100754A1) based on this singlet fission platform.

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Supplementary information

Supplementary information

Supplementary Figs. 1–14, Supplementary Tables 1 and 2, Supplementary materials and methods, Supplementary data and analysis

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Pun, A.B., Asadpoordarvish, A., Kumarasamy, E. et al. Ultra-fast intramolecular singlet fission to persistent multiexcitons by molecular design. Nat. Chem. 11, 821–828 (2019). https://doi.org/10.1038/s41557-019-0297-7

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