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Stimulus‐responsive molecular photochromic materials have potential applications in sensor, information storage, and optical switch devices since they undergo reversible color changes upon stimulus from external light. In this work, a viologen‐derived Mg(II) coordination complex with molecular formula [Mg(dpbp)2(H2O)4] (1) has been synthesized from 1‐(3,5‐dicarboxyphenyl)‐4,4′‐bipyridinium chloride (H2dpbp⋅Cl) under solvothermal conditions. Complex 1 has a three‐dimensional viologen‐based hydrogen bond network showing reversible photochromism through radical formation under ultraviolet‐visible light irradiation. Simultaneously, the emission of complex 1 can be reversibly modulated by ultraviolet‐visible light irradiation. Importantly, due to its reversible photochromic properties, practical fading time, and high stability, complex 1 can be used as an ink‐free and erasable printing medium by applying ultraviolet visible light irradiation with a mask. [ABSTRACT FROM AUTHOR]

Photochromic materials coupled with photoswitchable luminescence functionalities are of particular interest due to their potential applications in switches and optical memory devices. However, the construction of such materials, especially those with two-color emission states, is still challenging. In this context, a rare Zn7 cluster-based host–guest MOF material, (bbmp)[Zn7(IPA)6(OH)4(H2O)2] (1) (H2IPA = isophthalic acid, bbmp·2I = 4,4′-([1,1′-biphenyl]-4,4′-diyl)bis(1-methylpyridin-1-ium) diiodide), was prepared by encapsulating an organic cation into an anionic MOF produced from zinc cations and isophthalic acid ligands, which exhibits reversible naked detectable photochromic properties varying from yellow to green upon UV-Vis light irradiation. The photoactive guest bbmp2+ and the short O⋯N+ distances between the oxygen atoms of the carboxylate groups and the pyridine ring play a crucial role in the photochromism of this compound. More interestingly, the luminescence color of this cluster-based host–guest material can be reversibly switched from green to blue upon irradiation, exhibiting photoswitchable luminescence properties. [ABSTRACT FROM AUTHOR]

Organic amines are ubiquitous and essential in the dye, polymer, and pharmaceutical industries, but can also be highly corrosive and toxic. Developing a quick and efficient method to detect organic amines is an important challenge. In this paper, we demonstrate the detection of organic amines by colorimetric and luminescence sensing of an electron-deficient viologen metal organic material. The material, comprising 1-(3,5-dicarboxyphenyl)-4,4′-bipyridinium and Cd(II), possesses a two-dimensional framework with viologen-lined chromophores and accessible electron-deficient viologen moieties constituting Lewis acidic sites. It exhibits reversible photochromic behavior under UV–Vis light irradiation and a visual color change and fluorescence quenching upon contact with amine vapors and solutions. Due to the defined pore size of the framework, the fluorescence sensing efficiency showed organic amine size dependence. The vapochromism and fluorescence quenching is attributable to electron transfer from the organic amine to the electron-deficient viologen moiety, generating colored viologen radicals. An electron-deficient metal-organic material has successfully synthesized based on the viologen ligand, which exhibit reversible photochromic behavior and selective colorimetric and luminescence sensing of organic amines. [Display omitted] • An electron-deficient viologen metal-organic material was prepared. • Compound 1 exhibit reversible photochromic behavior under UV–visible light irradiation. • Complex 1 shows colorimetric and luminescence sensing of organic amines. [ABSTRACT FROM AUTHOR]

• A MOF based on electron-deficient naphthalene diimide dye is prepared. • The anion–π interactions between two-dimensional network and W6O192– is observed. • Complex 1 exhibits eye-detectable fast-responsive reversible photochromism and photoresponsive luminescence. • Photoinduced electron-transfer produces NDI radicals and W5+ species. 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 W 6 O 19 2– polyanions, [Ce 2 (BINDI) (DMF) 8 ]·[W 6 O 19 ] (1), (H 4 BINDI = 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 W 6 O 19 2– and expanded π–electron deficient naphthalene diimide (NDI) moieties. Moreover, because of the presence of electron-deficient NDI moieties and photoactive W 6 O 19 2–, 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. [Display omitted]. [ABSTRACT FROM AUTHOR]

The encapsulation of photoactive guests into a metal-organic framework is advantageous in endowing extra functionalities such as photochromism and photoswitchable luminescence. In this paper, a host-guest MOF material, [Zn 3 (IPA) 4 ​MV] (1) (H 2 IPA ​= ​isophthalic acid, MV·2NO 3 ​= ​1,1'-dimethyl-(4,4'-bipyridine)-1,1'-diium dinitrate) has been constructed by encapsulating simplest methyl viologen guest into the anionic MOF framework. This material exhibits reversible naked-eye detectable photochromic properties varying from colorless to blue upon UV–Vis light irradiation. The MV2+ and the short O⋯N distance between the oxygen atom and pyridine ring of MV2+ play a crucial role in the photochromism of this compound. This host-guest MOF compound shows photoswitchable luminescent properties in the solid state. More interestingly, this host-guest MOF material can be deposited on filter paper and can be employed as inkless print material by controlling the UV–Vis light irradiation with the stencil. A novel MOF-based host-guest compound was prepared by incorporating the photoactive methyl viologen into the anionic framework, which exhibit photochromism upon UV–Vis light irradiation and photocontrolled luminescence. Moreover, this compound can be used as inkless and erasable print media. [Display omitted] • A host-guest compound was prepared by incorporating the viologen into the anionic MOFs. • Compound 1 exhibits fast-responsive photochromism and reversible luminescence switching upon UV–Vis light irradiation. • Compound ​ 1 ​can be employed as inkless and erasable print media by controlling the UV-Vis light irradiation. [ABSTRACT FROM AUTHOR]