Picosecond x-ray diffraction probed transient structural changes in organic solids

In this Letter, we report on the experimental characterization of the geome try of short-lived electronically excited states in organic solids by time- resolved x-ray diffraction. Here, the structure factor of the organic cryst al is measured as a function of time. Since this technique gives complete s tructural information, it is a very useful tool for learning more about ato m motions on the excited-state energy surface-"beyond" the broad band typic al of conventional spectroscopy. Although we used molecular crystals rather than free molecules, the compounds show detectable transient structural ch anges on the ps to ns time scale in our study.