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

Abstract

In this work, two novel donor–acceptor (D–A) hybrid crystalline materials based on N,N′-4,4′-bipyridinio-dipropionate (H₂BpydpCl₂), (H₂Bpydp)₃[Fe^III(CN)₆]₂·4H₂O (1) and (H₂Bpydp)₃[Co^III(CN)₆]₂·4H₂O (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.