title: Evidence for point transformations in photoactive molecular crystals by the photoinduced creation of diffuse diffraction patterns.
abstract: Time-resolved diffuse X-ray scattering is one powerful method for monitoring the progression from the creation of local structural changes inside a crystalline material up to the transformation of the whole crystalline bulk. In this work, we study the mechanism of phototransformation of a molecular crystal by time-resolved diffuse X-ray scattering. Here, an optical excitation source, like a pulsed laser, initiates structural transformations which are monitored by X-ray scattering techniques. We have studied the dimerization process of the molecular switch α-styrylpyrylium (trifluoromethanesulfonate) TFMS, in particular for understanding whether cooperative effects influence the changes of the structure in the bulk and its periodicity. Upon illumination with optical light, α-styrylpyrylium TFMS instantaneously photoswitches. Depending on the optical fluence, X-ray diffuse planes are observed prior to phototransformation of the bulk. In the early stages of transformation, the analysis reveals systems of randomly distributed islands of product clusters with gradual growth in size and amount. The degree of transformation follows the optical excitation profile, i.e., the spatial absorption of the laser beam. In the present studies, no influence of cooperativity on the photodimerization process has been found.
authors.affiliation: IFG Structural Dynamics of (Bio)chemical Systems, Max Planck Institute for Biophysical Chemistry, 37070 Göttingen, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Hallmann
authors.forename: Rene
authors.initials: R
authors.lastname: More
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Morgenroth
authors.forename: Carsten
authors.initials: C
authors.lastname: Paulmann
authors.forename: Qingyu
authors.initials: Q
authors.lastname: Kong
authors.forename: Michael
authors.initials: M
authors.lastname: Wulff
authors.forename: Simone
authors.initials: S
authors.lastname: Techert
mesh_terms: D003460:Crystallization; D019281:Dimerization; D055668:Photochemical Processes; D011714:Pyrans / Q000737:chemistry*; D013343:Styrenes / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D011714:Pyrans; D013343:Styrenes; C546161:alpha-styrylpyrylium