Metal-cyanide hybrid materials exhibiting photochromic and photomagnetic responses based on viologen receptors

In this work, two novel donor-acceptor (D-A) hybrid crystalline materials based on N,N '-4,4 '-bipyridinio-dipropionate (H2BpydpCl2), (H2Bpydp)3[FeIII(CN)6]2 center dot 4H2O (1) and (H2Bpydp)3[CoIII(CN)6]2 center dot 4H2O (2), combining photoactive organic and inorganic components, as potential photochromic and photomagnetic materials are presented. Compound 1 demonstrates pronounced light-responsive behavior, showcasing reversible color changes and photoreduction of Fe, which are visible to the naked eye. In contrast, due to the optical inertness of Co, complex 2 does not display noticeable color changes. Furthermore, photomagnetic characteristics are observed during the photochromic process of 1, with a substantial 48% increase in the direct current (dc) magnetic susceptibility and shift of dynamic magnetic relaxation time derived from Fe spin center pre- and post-irradiation. A photochromic material based on viologen was synthesized. During the photo-induced color transition, the DC magnetic susceptibility was enhanced by 48%, and an increase in the magnetic relaxation time after illumination was observed.