Ultrafast two-colour X-ray emission spectroscopy reveals excited state landscape in a base metal dyad

TL;DR

This study employs ultrafast two-colour X-ray emission spectroscopy combined with optical spectroscopy and DFT calculations to directly observe and understand the electron transfer dynamics in a base metal dyad catalyst for hydrogen production.

Contribution

It introduces a novel two-colour X-ray emission spectroscopy method to simultaneously monitor Fe and Co in real-time, revealing electron transfer mechanisms in base metal dyads.

Findings

Direct evidence of Fe->Co electron transfer during photocatalysis.

Correlation of excited state dynamics with charge transfer processes.

Enhanced understanding of electron transfer in base metal dyads for sustainable catalysis.

Abstract

Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light induced proton reduction systems. For a more sustainable future, development of competitive base metal dyads is mandatory. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored. We study a Fe-Co dyad that exhibits photocatalytic H2 production activity using femtosecond X-ray emission spectroscopy, complemented by ultrafast optical spectroscopy and theoretical time-dependent DFT calculations, to understand the electronic and structural dynamics after photoexcitation and during the subsequent charge transfer process from the FeII photosensitizer to the cobaloxime catalyst. Using this novel approach, the simultaneous measurement of the transient Kalpha X-ray emission at the iron and cobalt K-edges in a two-colour experiment is enabled making it possible to correlate the excited state dynamics to the electron transfer processes. The methodology, therefore, provides a clear and direct spectroscopic evidence of the Fe->Co electron transfer responsible for the proton reduction activity.