Entanglement of states is one of the most surprising and counter-intuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which mediates the spin-conserving fission of one spin-0 singlet exciton into two spin-1 triplet excitons. Despite long theoretical and experimental exploration, the nature of the triplet-pair state and inter-triplet interactions have proved elusive. Here we use a range of organic semiconductors that undergo singlet exciton fission to reveal the photophysical properties of entangled triplet-pair states. We find that the triplet pair is bound with respect to free triplets with an energy that is largely material independent (∼30 meV). During its lifetime, the component triplets behave cooperatively as a singlet and emit light through a Herzberg-Teller-type mechanism, resulting in vibronically structured photoluminescence. In photovoltaic blends, charge transfer can occur from the bound triplet pairs with >100% photon-to-charge conversion efficiency.

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Published in Nature Communications, v. 8, article no. 15953, p. 1-12.

© The Author(s) 2017

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We thank the G8 Research Councils Initiative on Multilateral Research Funding (EPSRC EP/K025651; US National Science Foundation CMM1-1255494; Japanese Society for the Promotion of Science). J.C. thanks the University of Sheffield for a VC fellowship. A.J.M., J.C. and S.L.B. thank EPSRC (EP/M025330, EP/M01083X and EP/M025330). The work in Mons is supported by BELSPO through the PAI P6/27 Functional Supramolecular Systems project and by the Belgian National Fund for Scientific Research FNRS/F.R.S. D.B. is a Research Director of FNRS.

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The data that support the findings shown in both the main figures and Supplementary Figures in this study are available with the identifier https://doi.org/10.17863/CAM.9032.

ncomms15953-s1.pdf (9157 kB)
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