title: 100 picosecond diffraction catches structural transients of laser-pulse triggered switching in a spin-crossover crystal.
abstract: We study by 100 picosecond X-ray diffraction the photo-switching dynamics of single crystal of the orthorhombic polymorph of the spin-crossover complex [(TPA)Fe(TCC)]PF(6), in which TPA = tris(2-pyridyl methyl)amine, TCC(2-) = 3,4,5,6-Cl(4)-Catecholate(2-). In the frame of the emerging field of dynamical structural science, this is made possible by using optical pump/X-ray probe techniques, which allow following in real time structural reorganization at intra- and intermolecular levels associated with the change of spin state in the crystal. We use here the time structure of the synchrotron radiation generating 100 picosecond X-ray pulses, coupled to 100 fs laser excitation. This study has revealed a rich variety of structural reorganizations, associated with the different steps of the dynamical process. Three consecutive regimes are evidenced in the time domain: 1) local molecular photo-switching with structural reorganization at constant volume, 2) volume relaxation with inhomogeneous distribution of local temperatures, 3) homogenization of the crystal in the transient state 100 µs after laser excitation. These findings are fundamentally different from those of conventional diffraction studies of long-lived photoinduced high spin states. The time-resolution used here with picosecond X-ray diffraction probes different physical quantities on their intrinsic time-scale, shedding new light on the successive processes driving macroscopic switching in a functionalized material. These results pave the way for structural studies away from equilibrium and represent a first step toward femtosecond crystallography.
authors.affiliation: Institut de Physique de Rennes, UMR 6251 UR1-CNRS, Bat 11 A Campus de Beaulieu, University Rennes 1, 35042 Rennes Cedex, France. eric.collet@univ-rennes1.fr
authors.forename: Eric
authors.initials: E
authors.lastname: Collet
authors.forename: Maciej
authors.initials: M
authors.lastname: Lorenc
authors.forename: Marco
authors.initials: M
authors.lastname: Cammarata
authors.forename: Laurent
authors.initials: L
authors.lastname: Guérin
authors.forename: Marina
authors.initials: M
authors.lastname: Servol
authors.forename: Antoine
authors.initials: A
authors.lastname: Tissot
authors.forename: Marie-Laure
authors.initials: ML
authors.lastname: Boillot
authors.forename: Hervé
authors.initials: H
authors.lastname: Cailleau
authors.forename: Marylise
authors.initials: M
authors.lastname: Buron-Le Cointe