Photoselective MLCT to d-d pathways for light-induced excited spin state trapping

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• Spin-crossover materials exhibit switching between low-spin (LS) and high-spin (HS) states.
• Light Induced Excited Spin State Trapping (LIESST) is a phenomenon where light induces a transition from LS to HS states.
• This transition involves intermediate electronic states and structural changes, including molecular breathing modes.

Purpose of the Study:

• To investigate the pump wavelength dependence of LIESST dynamics.
• To explore photoselective control over LIESST pathways in Fe(II) spin-crossover materials.
• To compare LIESST dynamics initiated via metal-to-ligand charge transfer (MLCT) and d-d electronic transitions.

Main Methods:

• Femtosecond optical pump-probe spectroscopy was employed.
• The study focused on an Fe(II) spin-crossover material with Fe(II)N4O2 ligand field of C2 symmetry.
• Pump wavelength dependence of LIESST was analyzed.

Main Results:

• Optical excitation via d-d bands, in addition to MLCT bands, can drive LIESST.
• d-d excitation leads to shorter-lived intermediates, faster LS-to-HS switching, and enhanced coherent structural dynamics compared to MLCT.
• A photoselective crossover between MLCT and d-d pathways was evidenced.

Conclusions:

• The excitation pathway significantly influences LIESST dynamics and the resulting structural responses.
• Photoselective control over LIESST is achievable by tuning the excitation wavelength.
• This offers new possibilities for manipulating spin-state dynamics in materials.