This talk will focus on the use of ultrafast infrared spectroscopy as a probe of correlated triplet pair dynamics and separation following singlet fission in pentacene derivatives. The method can be used to probe the spatial separation of triplet pair intermediates on ultrafast time scales through two types of transitions that provide complementary information. When triplet pair states overlap neighboring molecules, they exhibit broad electronic transitions that arise from mixing of singlet exciton and net singlet spin correlated triplet pair states. As the triplet pair states dissociate on the picosecond to nanosecond time scale, their coupling to the singlet exciton states is diminished, which leads to loss of the broad electronic transition. In this way, triplet pair separation can be probed directly on ultrafast time scales. Simultaneously, triplet excitons exhibit distinct vibrational frequencies that are perturbed by the change in symmetry and electronic spatial distribution as they transition from singlet to triplet spin states. The dynamics of triplet pair separation measured through their vibrational features quantitatively matches their dynamics measured through the loss of the broad electronic transition, demonstrating that the intermediates responsible for determining the ultimate rate and yield of triplet exciton multiplication can be directly probed using ultrafast infrared spectroscopy.

Dynamics and separation of triplet pair intermediates in singlet fission measured with ultrafast infrared spectroscopy

2019 Fall National Meeting

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