Tracking polar solvation dynamics of a photoexcited organic chromophore with ultrafast X-ray scattering
- Kerstin M. Mitterer
- Elli Selenius
- Morten L. Haubro
- Magnus A. H. Christiansen
- Verena Markmann
- Bianca L. Hansen
- Mikkel Krell-Jørgensen
- Joseph G. F. Hoock
- Victor Lorentzen
- Emma V. Beale
- Philip J. M. Johnson
- David J. Gosztola
- Claudio Cirelli
- Camila Bacellar
- Asmus O. Dohn
- Luca Laraia
- Klaus B. Møller
- Kristoffer Haldrup
- Gianluca Levi
- Martin M. Nielsen
2026-04-13
Solvation plays a key role in many photochemical and biological processes. Yet, direct atomic-scale observation of solvent reorganization around photoexcited molecules containing only light atoms has so far remained elusive. Here, we use time-resolved X-ray scattering at an X-ray free-electron laser to track with a ~ 120 fs time resolution the photoinduced ultrafast rearrangement of polar acetonitrile solvent molecules around an organic hemithioindigo chromophore. The experiments reveal that the solvation shell reorganizes with a ~ 0.3 ps time constant driven by photoinduced charge transfer in the chromophore, and then reequilibrates over ~ 3 ps as the excited state population returns to the ground state. These results demonstrate the viability of using ultrashort X-ray pulses to directly visualize the motion of light atoms in solution, paving the way for atomic-scale understanding and control of photoinduced processes in biological and synthetic photoactive organic molecules.