# Unraveling Charge and Energy Transfer in a Singlet Fission Donor–Acceptor Complex: An Ab Initio Quantum Dynamical Study

## TL;DR

This study explores how energy and charge transfer occur in a donor-acceptor complex that undergoes singlet fission, a process that could improve solar cell efficiency.

## Contribution

The paper introduces a combined ab initio and quantum dynamical approach to uncover the mechanisms of charge and energy transfer in a singlet fission system.

## Key findings

- Intermolecular singlet fission occurs in the donor-acceptor complex.
- Charge and energy transfer follow intramolecular singlet fission.
- Energy loss decay channels compete with charge and energy transfer.

## Abstract

Singlet fission is a photophysical process in organic
molecules
that generates two triplet electronic states from an excited singlet
electronic state. Molecules exhibiting singlet fission can multiply
charge carriers and thus have the potential to enhance the performance
of solar cells beyond the Shockley–Queisser limit by reducing
thermalization losses. However, in order to implement singlet fission
for applications in photovoltaics, it is essential to understand how
charge or energy can be harvested from triplet excitons. In this work,
we investigate these processes in a prototypical donor–acceptor
complex consisting of a bis­(diazadiborine)-based chromophore as a
singlet fission-active donor and tetracyanoquinodimethane as an acceptor
molecule. Using a combined approach of high-level ab initio multireference perturbation theory techniques and quantum dynamical
simulations, we show the existence of intermolecular singlet fission,
charge and energy transfer following intramolecular singlet fission,
and energy loss decay channels to low-lying states as the three competing
charge and energy transfer mechanisms from the donor to the acceptor
molecule. We analyze the role of the different electronic states,
specific vibrational modes, and vibronic couplings in these processes.
The results provide insights into the rational design of donor–acceptor
systems with efficient singlet fission-based charge and energy transfer.