Direct observation of nuclear reorganization driven by ultrafast spin transitions.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32251278.
- Also identified by DOI 10.1038/s41467-020-15187-y and PMC identifier 7090058.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
One of the most basic molecular photophysical processes is that of spin transitions and intersystem crossing between excited states surfaces. The change in spin states affects the spatial distribution of electron density through the spin orbit coupling interaction. The subsequent nuclear reorganization reports on the full extent of the spin induced change in electron distribution, which can be treated similarly to intramolecular charge transfer with effective reaction coordinates depicting the spin transition. Here, single-crystal [Fe<sup>II</sup>(bpy)<sub>3</sub>](PF<sub>6</sub>)<sub>2</sub>, a prototypical system for spin crossover (SCO) dynamics, is studied using ultrafast electron diffraction in the single-photon excitation regime. The photoinduced SCO dynamics are resolved, revealing two distinct processes with a (450 ± 20)-fs fast component and a (2.4 ± 0.4)-ps slow component. Using principal component analysis, we uncover the key structural modes, ultrafast Fe-N bond elongations coupled with ligand motions, that define the effective reaction coordinate to fully capture the relevant molecular reorganization.