The magnetization dynamics on the photo-induced metastable state were also investigated, and the ac susceptibility measurement was performed under different applied dc field up to 10000 Oe external dc field and using the frequency ranging from 1 Hz to 1500 Hz at 1.9 K (Fig. ). No slow relaxation of magnetization was detected for 1 after light irradiation, although such fascinating magnetization dynamics involving slow relaxation of magnetization have been reported in a similar photo-induced metastable state for some Fe-Co chain. In conclusion, using [Fe III (Tp)(CN)3] ─ as a building block, and 1vinylimidazole as the blocking ligand on Co(II) side, two cyanidobridged Fe-Co 1D diamagnetic chains (1 and 2) are reported. Photo-induced metal-to-metal electron transfer strongly depends upon the geometry of the bridging cyanide linkers and Please do not adjust margins Please do not adjust margins the cooperativity coming from the hydrogen bonding interaction. Despite a similar chemical environment around iron and cobalt sites, i.e., FeC3N3 and CoN6, 1 showed photo-induced MMET coupled with spin state change, whereas 2 was photoinactive. The conversion of diamagnetic state to paramagnetic state is successfully established under light-irradiation and the photo-induced metastable state is thermally stable up to 80 K.