Spin Crossover in Transition Metal Compounds II

Volume 234 of the series Topics in Current Chemistry pp 155-198

Light-Induced Spin Crossover and the High-Spin→Low-Spin Relaxation

  • Andreas HauserAffiliated withDépartement de chimie physique, Bâtiment de Science II, Université de Genève Email author 

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The discovery of a light-induced spin transition at cryogenic temperatures in a series of iron(II) spin-crossover compounds in 1984 has had an enormous impact on spin-crossover research. Apart from being an interesting photophysical phenomenon in its own right, it provided the means of studying the dynamics of the intersystem crossing process between the high-spin and the low-spin state in a series of compounds and over a large temperature range. It could thus be firmly established that intersystem crossing in spin-crossover compounds is a tunnelling process, with a limiting low-temperature lifetime below 50 K and a thermally activated region above 100 K. This review begins with an elucidation of the mechanism of the light-induced spin transition, followed by an in depth discussion of the chemical and physical factors, including cooperative effects, governing the lifetimes of the light-induced metastable states.


Thermal and light-induced spin crossover High-spin→low-spin relaxation Intersystem crossing External pressure Chemical pressure Cooperative effects Iron(II) complexes