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Femtosecond Raman Microscopy Reveals Structural Dynamics Leading to Triplet Separation in Rubrene Singlet Fission
journal contribution
posted on 2017-11-25, 07:07 authored by Kajari Bera, Christopher J. Douglas, Renee R. FrontieraSinglet fission generates
multiple excitons from a single photon,
which in theory can result in solar cell efficiencies with values
above the Shockley–Queisser limit. Understanding the molecular
structural dynamics during singlet fission will help to fabricate
efficient organic photovoltaic devices. Here we use femtosecond stimulated
Raman spectroscopy to reveal the structural evolution during the triplet
separation in rubrene. We observe vibrational signatures of the correlated
triplet pair, as well as shifting of the vibrational frequencies of
the 1430 and 1542 cm–1 excited state modes, which
increase by more than 25 cm–1 in 5 ps. Our results
indicate that the correlated pair separation into two individual triplets
occurs concurrently with the loss of electron density from the tetracene
backbone in rubrene. This study provides new insights into the triplet
separation process and proves the utility of structurally sensitive
ultrafast vibrational techniques to understand the mechanism of singlet
fission.