In recent years, it has been recognized that an intermolecular mechanism known as singlet fission could increase the maximum thermodynamic energy conversion efficiency of certain photovoltaics by as much as 50%. Singlet fission is a spin-allowed process whereby one singlet excited state creates a pair of triplets on neighboring molecules. We have investigated the dynamics of singlet fission within a variety of carotenoid assemblies. The systems include aggregates (nanoparticles) composed of thousands of carotenoids, or small multimers, or covalently-bound dimers. The excited-state dynamics of these systems are probed with transient absorption spectroscopy, and time-resolved resonance Raman spectroscopy. Triplet formation occurs within one picosecond for all carotenoid assemblies of our experiments, and the yields approach 200% (i.e. two triplets per absorbed photon). The application of the carotenoid assemblies to photovoltaics is probably limited because of rapid annihilation of the triplet excitons, as well as their relatively low energy. Nevertheless, these studies provide fundamental insights into the singlet fission process.

Singlet fission in carotenoid aggregates and dimers

249th National Meeting (2015)

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