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Energy transport

Singlet to triplet and back again

Nature Chemistry volume 7, pages 764–765 (2015)Cite this article

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Spin-triplet excitations commonly migrate through direct electron exchange between neighbouring molecules. Now, experiments show that back-and-forth interconversion between spin-triplet and spin-singlet states can significantly speed up triplet migration in organic crystals.

The absorption of visible light by a molecule typically creates an excited electronic state that will subsequently relax through one of a number of potential pathways, be it through the emission of a photon or by transferring its energy to its surroundings as heat. However, in some cases an electron can relax by using some, but not all, of its energy to excite a second electron on a neighbouring molecule. In materials that possess low-energy triplet levels, such as some extended polycyclic aromatic hydrocarbons and long-chain polyenes, it is possible for high-energy singlet excitons (excited electron–hole pairs) to relax by generating a pair of spin-correlated triplet excitons. This process, known as singlet fission1, was first reported in the mid 1960s but has found renewed interest because it could potentially boost solar cell photocurrents by generating more than one excited electron from a single photon2. However, building devices that benefit from singlet fission requires an understanding of how these materials transport energy. Now, writing in Nature Chemistry, Huang and colleagues3 have discovered that careful balancing of the singlet and triplet energies of singlet-fission materials can be used to significantly enhance the rate with which these materials move energy.

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Figure 1: Illustration showing how femtosecond microscopy experiments track cooperative energy transport in tetracene crystals.

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Authors and Affiliations

  1. Sean T. Roberts is in the Department of Chemistry, University of Texas at Austin, 105 24th Street Stop A5300, Austin, Texas 78712, USA,

    Sean T. Roberts

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  1. Sean T. Roberts
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Correspondence to Sean T. Roberts.

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Roberts, S. Singlet to triplet and back again. Nature Chem 7, 764–765 (2015). https://doi.org/10.1038/nchem.2356

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