Reversible photochromism and photoresponsive luminescence in naphthalene diimide-based framework with Lindqvist-type polyoxometalate template

Metal-organic frameworks that contain photoactive organic ligands or photoactive inorganic components are an emerging class of multifunctional hybrid materials that in recent years has gradually become an ideal platform for building photochromic complexes. In this paper, a metal-organic framework based on naphthalene diimide (NDI) ligand with Lindqvist-type W6O192– polyanions, [Ce2(BINDI) (DMF)8]·[W6O19] (1), (H4BINDI = N, N'-bis(5-isophthalic acid)-1,4,5,8-naphthalene diimide) was synthesized and systematically characterized. It displays a cationic two-dimensional grid coordination network, featuring anion–π interactions between W6O192– and expanded π–electron deficient naphthalene diimide (NDI) moieties. Moreover, because of the presence of electron-deficient NDI moieties and photoactive W6O192–, this complex exhibits fast responsive reversible photochromism and photoresponsive tunable luminescence. UV–Vis, IR, PXRD, EPR, and XPS spectral studies indicate that the obviously photochromic phenomenon of complex 1 is derived from photoinduced electron-transfer form NDI radicals and W5+ species.