Light induced excited spin state trapping in the binuclear spin crossover compound [Fe(bpym)(NCS)2]2(bpym) exhibiting a high-spin ground state

A photo-magnetic effect is evidenced using near-infrared light in the binuclear complex [Fe(bpym)(NCS)2]2(bpym). This compound has a 5T2g–5T2g ground state and exhibits no thermal spin crossover – in contrast to the analogous [Fe(bpym)(NCSe)2]2(bpym). The estimated photo-conversion ratio is ca. 30%. By means of magnetic susceptibility measurements as well as Raman and infrared absorption spectroscopies, the nature of the photo-induced phase was established as the 5T2g–1A1g state, which means that only one iron center is converted to low-spin. The photo-induced state was completely converted back to the ground state either by visible light excitation or by heating.