Structural Dynamics upon Photoexcitation in a Spin Crossover Crystal Probed with Femtosecond Electron Diffraction

Angewandte Chemie - International Edition

5 years ago

Structural Dynamics upon Photoexcitation in a Spin Crossover Crystal Probed with Femtosecond Electron Diffraction

$Structural Dynamics upon Photoexcitation in a Spin Crossover Crystal Probed with Femtosecond Electron Diffraction$

Henrike M. Müller-Werkmeister, Cheng Lu, Yifeng Jiang, Dongfang Zhang, Antoine Sarracini, Eric Collet, R. J. Dwayne Miller, Lai Chung Liu, Gustavo Moriena, Ryan L. Field

Photoexcitation of spin crossover (SCO) complexes can trigger extensive electronic spin transitions and transformation of molecular structure. However, the precise nature of the associated ultrafast structural dynamics remains elusive, especially in the solid state. Here, we studied a single-crystal SCO material with femtosecond electron diffraction (FED). The unique capability of FED allows us to directly probe atomic motions and to track ultrafast structural changes within a crystal lattice. By monitoring the time-dependent changes of the Bragg reflections, we observed the formation of a photoinduced structure similar to the thermally induced high-spin state. The data and refinement calculations indicate the global structural reorganization within 2.3 ps, as the metal–ligand bond distribution narrows during intramolecular vibrational energy redistribution (IVR) driving the intermolecular rearrangement. Three independent dynamical group are identified to model the structural dynamics upon photoinduced SCO. Ultrafast: Femtosecond electron diffraction has been used to directly study the structural dynamics in the spin crossover compound [Fe(PM-AzA)2](NCS)2. Three dynamic modes, which all occur with a time constant of 2.3 ps are found: metal–ligand bond elongation, ligand motion, and local unit cell expansion, driven by the narrowing of the metal–ligand bond distribution during the vibrational cooling process.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201702497