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Fig. 50: Time-evolution of the observed structural changes. a) Typical 2D powder diffraction pattern measured on micro-crystals at quasi-grazing incidence. b-c) Time evolution of the unit cell volume (V), and of the relative high spin state fraction (ΔXHS), retrieved by Pawley method after azimuthal integration of 2D patterns.

Fig. 51: Principal steps resolved in non-equilibrium dynamics of the photo-induced low-spin to high-spin transition. 1: Charge transfer promotes Low Spin (LS) molecules residing in LS lattice to a hot High spin (HS) state. 2: Vibrational cooling of hot molecules with LS lattice. 3: Volume expansion of the lattice, and coexistence of LS molecules in thermally dilated LS lattice with photo-switched HS molecules in thermally dilated HS lattice. 4: Temporally incompressible Arrhenius-type kinetics and LS to HS conversion within ground states. 5: Recovery of thermal equilibrium.