Issue 24, 2025

Ultrafast solvent migration in an iron complex revealed by nonadiabatic dynamics simulations

Abstract

The response of a solvation shell to molecular solute photoexcitation is an ubiquitous phenomenon of great relevance in chemistry. This response can occur within just few tens of femtoseconds, making it very challenging to resolve experimentally. Thus, the details of the (an)isotropy of the solvent response around a solute, the presence of coherent solvent fluctuations, hydrogen bond reorganization mechanisms, and the intricate interplay between electronic, spin, nuclear, and solvent dynamics remain elusive. Here, we report large-scale nonadiabatic molecular dynamics simulations of [Fe(CN)4(bipy)]2− (bipy=2,2′-bipyridine) in water, where the electronic evolution from singlet metal-to-ligand charge transfer (MLCT) states to triplet MLCT and metal-centered (MC) states overlaps temporally with the molecule's nuclear motion and a strong solvent shell response. We leverage vibronic coupling model potentials combined with electrostatic embedding, within our so-called vibronic coupling/molecular mechanics (VC/MM) method, to be able to compute several thousand nonadiabatic excited-state trajectories, including all relevant singlet and triplet states as well as several thousand explicit water molecules. This superior statistics affords an unprecedented view on the three-dimensional solvent distribution dynamics at few-fs and sub-Å resolution. The results reveal a direct solvent migration mechanism, where excitation to the MLCT states leads to the breaking of hydrogen bonds to the cyanide ligands within less than 100 fs, followed by the formation of hydrogen bonds with the negatively charged bipyridyl ligand by the same water molecules. Furthermore, the MLCT and MC states show very distinct solvent responses, which are overlapping in time, as governed by the electronic dynamics. More broadly, this work demonstrates how VC/MM nonadiabatic dynamics simulations can resolve anisotropic solvent dynamics around a photoexcited solute with unprecedented detail, offering a new perspective that could stimulate the development of time-resolved experimental techniques capable of probing such solvent behaviour.

Graphical abstract: Ultrafast solvent migration in an iron complex revealed by nonadiabatic dynamics simulations

Supplementary files

Article information

Article type
Edge Article
Submitted
14 Feb 2025
Accepted
13 May 2025
First published
13 May 2025
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2025,16, 11128-11137

Ultrafast solvent migration in an iron complex revealed by nonadiabatic dynamics simulations

S. Polonius, L. González and S. Mai, Chem. Sci., 2025, 16, 11128 DOI: 10.1039/D5SC01174D

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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