Generalised Marcus Theory for Multi-Molecular Delocalised Charge Transfer

TL;DR

This paper extends Marcus theory to describe charge transfer involving delocalised molecular aggregates, enabling efficient analysis of complex systems and revealing how delocalisation can enhance or suppress transfer rates.

Contribution

It introduces a generalized Marcus theory that models charge transfer between molecular groups using their individual properties, avoiding costly supermolecular calculations.

Findings

Delocalisation can enhance charge transfer rates via supertransfer.

Charge transfer can be suppressed through subtransfer.

Tuning energy levels and reorganisation energies can optimize transfer rates.

Abstract

Although Marcus theory is widely used to describe charge transfer in molecular systems, in its usual form it is restricted to transfer from one molecule to another. If a charge is delocalised across multiple donor molecules, this approach requires us to treat the entire donor aggregate as a unified supermolecule, leading to potentially expensive quantum-chemical calculations and making it more difficult to understand how the aggregate components contribute to the overall transfer. Here, we show that it is possible to describe charge transfer between groups of molecules in terms of the properties of the constituent molecules and couplings between them, obviating the need for expensive supermolecular calculations. We use the resulting theory to show that charge delocalisation between molecules in either the donor or acceptor aggregates can enhance the rate of charge transfer through a process we call supertransfer (or suppress it through subtransfer). The rate can also be enhanced above what is possible with a single molecule by judiciously tuning energy levels and reorganisation energies. We also describe bridge-mediated charge transfer between delocalised molecular aggregates. The equations of generalised Marcus theory are in closed form, providing qualitative insight into the impact of delocalisation on charge dynamics in molecular systems.