Abstract
AbstractThe impact of molecular vibrations on singlet fission, which is the spontaneous fission of a singlet exciton into two triplet excitons, is studied using ultrafast optical spectroscopy for the prototypical singlet fission chromophores tetracene and pentacene. We modify the frequency of intramolecular vibrations by deuteration, without impacting thin film structure and molecular arrangement, and study the resulting changes in exo‐ and endothermic singlet fission rates by comparing the deuterated and parent chromophores. We find that changes in the frequency of the C−C deformation modes of Δω=6 cm−1 and the occurrence of C−D vibrational modes do not lead to significant modifications in the singlet fission time constants. We conclude that the changes in the frequency of phonon modes induced by deuteration are too small to significantly impact the electron–phonon coupling that drives the singlet fission process.
Highlights
Singlet fission (SF), the photophysical process converting a singlet exciton into two triplet excitons on neighboring molecules, holds promise for increasing solar cell efficiencies.[1]
We use broadband ultrafast transient absorption (TA) spectroscopy to characterize the SF process in neat thin films of dideuterated tetracene and dideuterated pentacene, where intramolecular vibrations are modified compared to the parent compounds, while the thin film structure and the molecular arrangement are not altered
To exclude any effects of structural changes on SF time constants, we investigated the impact of deuteration on the structural and optical properties of the films
Summary
Singlet fission (SF), the photophysical process converting a singlet exciton into two triplet excitons on neighboring molecules, holds promise for increasing solar cell efficiencies.[1]. Disentangling the contributions of inter- and intramolecular vibrations to SF is experimentally challenging, since a modification of vibrations via functionalization is often accompanied by changes in molecular arrangement. We use broadband ultrafast transient absorption (TA) spectroscopy to characterize the SF process in neat thin films of dideuterated tetracene and dideuterated pentacene, where intramolecular vibrations are modified compared to the parent compounds, while the thin film structure and the molecular arrangement are not altered. This allows us to solely study the impact of intramolecular vibrations on SF
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