Quantum dynamics simulation of intramolecular singlet fission in covalently linked tetracene dimer

TL;DR

This paper models the full quantum dynamics of singlet fission in covalently linked tetracene dimers, revealing a key coherent time scale and how energy transfer is influenced by vibrational modes, with implications for optimizing fission yield.

Contribution

It introduces a numerically unbiased quantum dynamical simulation of singlet fission in tetracene dimers, accounting for both excitonic and vibrational interactions, and explores how energy levels affect fission efficiency.

Findings

Identified a dominant coherent time scale of ~35 fs for singlet fission.

Found that a reduced set of phononic modes significantly influence energy transfer.

Showed that singlet fission yield can be doubled by tuning excitonic energy levels.

Abstract

In this work we study singlet fission in tetracene para-dimers, covalently linked by a phenyl group. In contrast to most previous works, we account for the full quantum dynamics of the combined excitonic and vibrational system. For our simulations we choose a numerically unbiased representation of the molecule's wave function enabling us to compare with experiments, exhibiting good agreement. Having access to the full wave function allows us to study in detail the post-quench dynamics of the excitons. Here, one of our main findings is the identification of a time scale $t_0 \approx 35 \text{fs}$ dominated by coherent dynamics. It is within this time scale that the larger fraction of the singlet fission yield is generated. We also report on a reduced number of phononic modes that play a crucial role for the energy transfer between excitonic and vibrational system. Notably, the oscillation frequency of these modes coincides with the observed electronic coherence time $t_0$. We extended our investigations by also studying the dependency of the dynamics on the excitonic energy levels that, for instance, can be experimentally tuned by means of the solvent polarity. Here, our findings indicate that the singlet fission yield can be doubled while the electronic coherence time $t_0$ is mainly unaffected.