Probing Charge Transfer Dynamics in a Single Iron Tetraphenylporphyrin Dyad Adsorbed on an Insulating Surface

TL;DR

This study investigates charge transfer dynamics in a single iron tetraphenylporphyrin dyad on an insulating surface, revealing initial state dependence and molecule-molecule tunneling as key factors, using STM imaging and DFT simulations.

Contribution

It demonstrates nanoscale control and imaging of charge transfer in a single molecule dyad, highlighting the role of initial states and coherent tunneling mechanisms.

Findings

Charge transfer efficiency depends on initial excited states.

Charge transfer occurs via molecule-molecule coherent tunneling.

Surface-mediated charge transfer is negligible.

Abstract

Although the dynamics of charge transfer (CT) processes can be probed with ultimate lifetime resolution, the helplessness to control CT at the nanoscale constitutes one of the most important road-blocks to revealing some of its deep fundamental aspects. In this work, we present an investigation of CT dynamics in a single iron tetraphenylporphyrin (Fe-TPP) donor/acceptor dyad adsorbed on a CaF2/Si(100) insulating surface. The tip of a scanning tunneling microscope (STM) is used to create local ionic states in one fragment of the dyad. The CT process is monitored by imaging subsequent changes in the neighbor acceptor molecule and its efficiency is mapped revealing the influence of the initial excited state in the donor molecule. In validation of the experiments, simulations based on density functional theory show that holes have a higher donor-acceptor CT rate compared to electrons and highlight a noticeable initial state dependence on the CT process. We leverage the unprecedented spatial resolution achieved in our experiments to show that the CT process in the dyad is governed via molecule-molecule coherent tunneling with negligible surface-mediated character.