Critical temperature of the LIESST effect in iron(II) spin crossover compounds

The light-induced crossover in a series of iron(II) compounds has been investigated by irradiating the sample at 10 K with a Kr+ laser coupled to an optical fiber within a SQUID cavity. The temperature dependence of the molar fraction of the light-induced metastable HS state has been recorded for 22 compounds. The critical LIESST temperature, Tc(LIESST), has been defined as the temperature for which the light-induced HS information was erased in the SQUID cavity. The dependence of Tc(LIESST) as a function of the thermal spin crossover temperature, T1/2, has been discussed. The effect of cooperation has been analyzed and the influence of horizontal and vertical displacements of the LS and HS potential wells has been discussed on the basis of the non-adiabatic multiphonon theory.