Spin transition behavior in molecular crystals has attracted wide attention in the field of molecular physics and chemistry. By appropriate chemical design, the transition properties (e.g. transition temperature) could be finely tuned. In this talk, we will discuss about the electron dynamics in two systems, i.e. [(Fe(RR-cth))(M(SS-cth))(μ-dhbq)]X 3 and [(Co(RR-cth))(M(SS-cth))(μ-dhbq)]X 3 crystallized in the P2 1 space group (cth = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, H 2 dhbq = 2,5-dihydroxy-1,4-benzoquinone, M = Co, Cr and Ga, X = PF 6 − and AsF 6 − ). The former family exhibits a transition process at Fe site with thermally hysteretic behavior, followed by a gradual electron transfer between the Fe and ligand sites. Owing to the asymmetrical changes in the molecular structures and changes in metal-ligand covalency, a substantial polarization change has been observed. Furthermore, these compounds undergo similar processes when subjected to pulsed magnetic fields at lower temperatures, resulting in a comparable polarization change. The latter family exhibits an electron transfer coupled spin transition process at Co site, which leads to a polarization change as large as 2~3 μC/cm 2 . Interestingly, by trapping the electron-transferred metastable state at low-temperatures, a persistent light-induced polarization change could be observed.

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