Fig. 7: Schematic of the proposed pathway of the photoinduced phase transition revealed by the UED and XRD experiments. | Nature Communications

Fig. 7: Schematic of the proposed pathway of the photoinduced phase transition revealed by the UED and XRD experiments.

From: Capturing ultrafast molecular motions and lattice dynamics in spin crossover film using femtosecond diffraction methods

Fig. 7: Schematic of the proposed pathway of the photoinduced phase transition revealed by the UED and XRD experiments.The alternative text for this image may have been generated using AI.

a A curved trajectory in the space defined by Fe−ligand elongation and ligand rotation presents a comprehensive picture of the sequential photo-switching dynamics down to the earliest fs timescale. Upon photoexcitation from the LS ground state, the molecule reaches the HS potential surface associated with an ultrafast Fe-ligand elongation through ISC processes. IVR activates ligand rotation, promoting further reorganization of the excited HS state (HS*) within the constant LT unit cell. b The scheme of photoexcitation cycle. 1: the pump laser excites a small fraction of the LS molecules (blue dots) in the LS lattice (blue grids) into hot HS molecules (red crosses) in less than 150 fs. 2: molecular vibrational cooling process happens in the constrained unit cell in a few picoseconds, transferring a great quantity of energy to the lattice. 3: As a result, the unit-cell volume expands with the propagation of strain wave in ~40 ps from blue solid lines to red dash lines, indicating a temporal decoupling between the volume expansion and molecular switching. 4: A second significant SCO step occurs in tens of nanosecond since the fraction of LS/HS molecules equilibrates with the new lattice conformation with expanded volume and elevated temperature. 5: The excited sample relaxes back to the initial ground state in 1 µs timescale15,16.

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