J. Phys. IV France 114 (2004) 99
DOI: 10.1051/jp4:2004114019

100 ps time-resolved crystallographic investigation of the photoinduced phase transition in TFF-CA

L. Guérin¹, E. Collet¹, M. Buron-Le Cointe¹, M.-H. Lemée-Cailleau¹, H. Cailleau¹, M. Wulff², S. Techert³ and Shin-Ya Koshihara<sup>4

1</sup>  Groupe Matière Condensée et Matériaux, UMR 6626, Université de Rennes 1, 35042 Rennes Cedex, France
    e-mail: laurent.guerin@univ-rennes1.fr
²  European Synchrotron Radiation Facility, BP. 220, 38043 Grenoble, France
³  Max-Plank-Institut fot Biophysical Chemistry, Department 010, 370070 Götingen, Germany
⁴  Department of Materials Science, Tokyo Institute of Technology, 2-12-1 Oh-okayama, Meguro-ku, Tokyo 152, Japan

Abstract
We report the structural investigation of photoinduced phase transitions between ionic and neutral macroscopic states in an organic charge-transfer molecular material, with 100 picosecond resolution, using pulsed X-rays from a synchrotron. A femtosecond laser pulse switches the material within the nanosecond from neutral to ionic and also from ionic to neutral macroscopic state by virtue of a strong cooperativity. Data collections show that a long range ferroelectric order takes place in the ionic photoinduced phase. A two step mechanism is observed in the transformation from ionic to neutral. This associated with a disordering process of ionic strings followed by a 3D reorganisation at a macroscopic scale. Key words. Photo-induced phase transition, Time-resolved x-ray diffraction.

© EDP Sciences 2004