Site-selective measurement of coupled spin pairs in an organic semiconductor.
Proceedings of the National Academy of Sciences of the United States of America
National Academy of Sciences
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Bayliss, S., Weiss, L., Mitioglu, A., Galkowski, K., Yang, Z., Yunusova, K., Surrente, A., et al. (2018). Site-selective measurement of coupled spin pairs in an organic semiconductor.. Proceedings of the National Academy of Sciences of the United States of America, 115 (20), 5077-5082. https://doi.org/10.1073/pnas.1718868115
From organic electronics to biological systems, understanding the role of intermolecular interactions between spin pairs is a key challenge. Here we show how such pairs can be selectively addressed with combined spin and optical sensitivity. We demonstrate this for bound pairs of spin-triplet excitations formed by singlet fission, with direct applicability across a wide range of synthetic and biological systems. We show that the site-sensitivity of exchange coupling allows distinct triplet pairs to be resonantly addressed at different magnetic fields, tuning them between optically bright singlet (S = 0) and dark triplet, quintet (S = 1, 2) configurations: this induces narrow holes in a broad optical emission spectrum, uncovering exchange-specific luminescence. Using fields up to 60 T, we identify three distinct triplet-pair sites, with exchange couplings varying over an order of magnitude (0.3-5 meV), each with its own luminescence spectrum, coexisting in a single material. Our results reveal how site-selectivity can be achieved for organic spin pairs in a broad range of systems.
This work was supported by HFMLRU/ FOM and LNCMI-CNRS, members of the European Magnetic Field Laboratory (EMFL) and by EPSRC (UK) via its membership to the EMFL (grant no. EP/N01085X/1 and NS/A000060/1) and through grant no. EP/M005143/1. L.R.W. acknowledges support of the Gates-Cambridge and Winton Scholarships. We acknowledge support from Labex ANR-10-LABX-0039-PALM, ANR SPINEX, and DFG SPP-1601 (Bi-464/10-2).
External DOI: https://doi.org/10.1073/pnas.1718868115
This record's URL: https://www.repository.cam.ac.uk/handle/1810/278248