Ultrafast Dynamics of Photo-induced Phase Transition in Transition Metal Molecular Materials Studied by Streaming Crystallography

We propose to investigate the dynamics of ultrafast and non-reversible photo-induced phase transitions using the “streaming crystallography” technique developed during our previous beamtimes (CH-6492 and CH-6162), that enables real time study of photo-induced phase transitions in molecular materials, within or outside thermal hysteresis. Previous experiments on Co-doped MnFe Prussian Blue Analogues revealed that conversion is completed within 200 ps, with global symmetry change driven by elastic cooperativity. Investigations at variable temperatures show only a very gentle effect in the transformation dynamics. To get better control of the phase transition, we propose here to modulate elastic properties of the crystals, by varying its composition (through doping) and by switching from bulk to surface excitation. Additionally, measurements will be performed on spin-crossover compounds, where the phase transition can occur with or without symmetry change, depending on composition.