Very Long-Lived Photogenerated High-Spin Phase of a Multistable Spin-Crossover Molecular Material

The
spin-crossover compound [Fe­(n-Bu-im)3(tren)]­(PF6)2 shows an unusual long relaxation
time of 20 h after light-induced excited spin state trapping when
irradiating at 80 K. This is more than 40 times longer than when irradiating
at 10 K. Optical absorption spectroscopy, magnetometry, and X-ray
diffraction using synchrotron radiation were used to characterize
and explain the different relaxation behaviors of this compound after
irradiation below and above 70 K. Rearrangement of the butyl chains
of the ligands occurring during the relaxation after irradiation above
70 K is thought to be responsible for the unusually long relaxation
time at this temperature.