Excited state small unit cell structure from ultrafast X-ray diffraction

Le résumé fourni par la source

Absorption of light in photoactive materials excites the electrons and this changes the atomic structures and properties. Ultrafast structural dynamics have been studied in biomolecular crystals using X-ray Free Electron Lasers, but direct experimental observation of short-lived atomic structures of small unit cell systems has remained elusive. The methodological gap mainly arises from the sparse sampling of reciprocal space, which complicates reliable data reduction. Using single crystal pump-probe serial X-ray crystallography, we here report direct structural characterization of a short-lived excited state in the inorganic molecular photocatalyst K4[Pt2(P2O5H2)4]∙2H2O. Structural changes ~1 ps after optical laser illumination are revealed by a model-independent difference Fourier map. Here, a Pt-Pt bond contraction of 0.65 Å is observed upon photoexcitation, which is assigned to population of the lowest-lying septet state according to Density Functional Theory calculations. Such structural characterizations of ultrafast excited states can assist in elucidating the atomic scale origin of essential properties in small unit cell photoactive materials, highlighting the importance of expanding the pump-probe diffraction methods to include these important systems.

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