Picosecond X-Ray Diffraction Probed Transient Structural Changes in Organic Solids

Abstract

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

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

“…Laser pump and X-ray probe techniques now provide an outstanding opportunity for the direct observation of a photoinduced structural phase transition as it takes place. The use of short X-ray pulses of about 100 ps around third-generation synchrotron sources allows exactly that (Collet et al, 2003;Guérin et al, 2004;Schotte et al, 2003;Techert et al, 2001). Other new X-ray sources, such as plasma ones (Rousse et al, 2001;Sokolowski-Tinten et al, 2003), generate ultra-short pulses down to 100 fs.…”

Excited-state structure by time-resolved X-ray diffraction

“…This limitation is now being removed as demonstrated by the rapid development of time-resolved biochemical crystallography, summarized in a recent review article (Moffat, 2001), and by a picosecond diffraction study of torsional distortions in the organic molecule N,N-dimethylaminobenzonitrile (DMABN) (Techert et al, 2001). A parallel development of the EXAFS technique has recently been applied in the ®rst time-resolved determination of the changes in coordination geometry in a transition-metal complex (Chen et al, 2001).…”

Picosecond soft x-ray absorption measurement of the photoinduced insulator-to-metal transition inVO2

“…To date, scientific applications of ultrafast x-rays have concentrated primarily on time-resolved diffraction measurements. This has been driven in part by developments in tabletop plasma-sources 3,4 , early laser-e-beam interaction schemes 5,6 , fast x-ray detectors 7 and synchrotron instrumentation 8 . Direct detection of photo-excited coherent acoustic 9,10,11 and optical phonons 12 , solid-liquid 13,14,15 and solid-solid 16,17 phase transitions have been recently demonstrated.…”