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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]

The incorporation of photochromic units into metal–organic frameworks (MOFs) is of particular interest due to their ability to endow the MOFs with extra functions such as photomodulated fluorescence, photomagnetism, and photomodulated electrical conductivity. In this work, a π-conjugated electron-deficient viologen ligand was assembled with La3+, resulting in a stable cationic MOF with one-dimensional channels, namely [La(bdpbpy)(H2O)2]·NO3·5H2O (1-NO3) (H4bdpbpy·2Cl = 1,1′-bis(3,5-dicarboxyphenyl)-4,4′-bipyridinium dichloride). As expected, 1-NO3 exhibits photochromism accompanied by an obvious color change from yellow to brown under UV-vis light irradiation. Remarkably, the water stable cationic framework of 1-NO3 acts as an efficient and selective trap for toxic dichromate through ion-exchange. The π-conjugated electron-deficient viologen ligand in the framework can provide extra affinity for iodine adsorption, and thus 1-NO3 exhibits sorption behaviours for iodine molecules. More importantly, the iodine adsorption capacity of 1-NO3 was significantly reduced when it was irradiated by UV-vis light. This is attributed to the photoinduced electron transfer (PET) changing the original charge distribution of the bipyridinium moieties on the channel and weakening the affinity for the N+⋯I–I interaction. This work breaks through the traditional design strategy to construct MOF adsorbent materials with controllable adsorption capacity. [ABSTRACT FROM AUTHOR]

Photochromic materials with tunable luminescence have attracted considerable interest owing to their potential applications in various fields. However, making such materials with expected properties has always been a challenge. In this work, two metal–organic framework based host–guest compounds, [MV]·[Cd3(TPDC)4] (1) and [MV]·[Cd2(BTC)2(H2O)] (2) (MV·2NO3 = 1,1′-dimethyl-(4,4′-bipyridinium)dinitrate; H2TPDC = thiophene-2,5-dicarboxylic acid; H3BTC = 1,3,5-benzenetricarboxylic acid), have been synthesized by incorporating photoactive methyl viologen into an anionic metal–organic framework formed from cadmium cations and polycarboxylic acid ligands. Due to the presence of photoactive methyl viologen, both compounds exhibit electron-transfer photochromic behavior not only towards sunlight and indoor light irradiation but also towards X-rays. The photochromic response of compounds 1 and 2 originates from the carboxyl group to methyl viologen electron transfer. More interestingly, compounds 1 and 2 show good luminescence emission and their luminescence can be modulated upon sunlight irradiation. [ABSTRACT FROM AUTHOR]

2,4,6‐Tris(pyridin‐4‐yl)‐1,3,5‐triazine (tpt), as an organic molecule with an electron‐deficient nature, has attracted considerable interest because of its photoinduced electron transfer from neutral organic molecules to form stable anionic radicals. This makes it an excellent candidate as an organic linker in the construction of photochromic complexes. Such a photochromic three‐dimensional (3D) metal–organic framework (MOF) has been prepared using this ligand. Crystallization of tpt with Cd(NO3)2·4H2O in an N,N‐dimethylacetamide–methanol mixed‐solvent system under solvothermal conditions afforded the 3D MOF poly[[bis(nitrato‐κ2O,O′)cadmium(II)]‐μ3‐2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine‐κ3N2:N4:N6], [Cd(NO3)2(C18H12N6)]n, which was characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and single‐crystal X‐ray diffraction. The X‐ray diffraction crystal structure analysis reveals that the asymmetric unit contains one independent CdII cation, one tpt ligand and two coordinated NO3− anions. The CdII cations are connected by tpt ligands to generate a 3D framework. The single framework leaves voids that are filled by mutual interpenetration of three independent equivalent frameworks in a fourfold interpenetrating architecture. The compound shows a good thermal stability and exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron‐transfer generation of radicals in the tpt ligand. A fourfold interpenetrating cadmium(II) metal–organic framework, which has been prepared using the 2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine ligand, exhibits prominent photochromic behaviour upon UV–Vis light irradiation. [ABSTRACT FROM AUTHOR]

Three newcadmiumcoordination polymers, namely [Cd(NO3)2(DPNDI)(CH3OH)]·CH3OH(1), [Cd(SCN)2(DPNDI)] (2), and [Cd(DPNDI)2(DMF)2]·2ClO4 (3) (DPNDI = N,N-di(4-pyridyl)-1,4,5,8- naphthalene diimide, DMF = N,N-dimethylformamide) have been synthesized by reactions of DPNDI with Cd(NO3)2, Cd(SCN)2, and Cd(ClO4)2, respectively. Compound 1 is a one-dimensional coordination polymer with strong lone pair-π interactions between the coordinated NO3 - anions and the imide ring of DPNDI; while 2 is a two-dimensional network with a (4, 4) net topology. In the case of 3, due to the presence of uncoordinated perchlorate counter ions, it exhibits a non-interpenetrated square-grid coordination polymer containing one-dimensional rhomboid channels. The structural diversity in these compounds is attributed to different coordination abilities and geometries of counter anions. Due to the presence of electron-deficient NDI moiety, the photochromic behavior of these compounds was studied. Interestingly, only compounds 1 and 3 exhibit color changes under light irradiation. The influence of the anions on the photochromism process of the NDI-based materials has been discussed. [ABSTRACT FROM AUTHOR]

Naphthalenediimides, a class of organic dyes with an expanded π-electron-deficient plane, have attracted considerable interest because of their photoinduced electron transfer from neutral organic moieties to stable anionic radicals. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic two-dimensional coordination polymer has been prepared using N, N′-bis(pyridin-4-ylmethyl)naphthalene-1,8:4,5-bis(dicarboximide) (DPMNI). In crystallization tubes, upon slow diffusion of an MeOH solution of cadmium perchlorate into a CHCl3 solution of DPMNI, the complex poly[[bis[μ2-2,7-bis(pyridin-4-ylmethyl)benzo[ imn][3,8]phenanthroline-1,3,6,8(2 H,7 H)-tetrone-κ2 N: N′]bis(perchlorato-κ O)cadmium(II)] chloroform tetrasolvate], {[Cd(C26H16N4O4)2(ClO4)2]·4CHCl3} n, (I), was obtained. The asymmetric unit contains one Cd2+ cation, two DPMNI ligands, two coordinated ClO4− anions and four CHCl3 solvent molecules. Each Cd2+ cation is interconnected by four DPMNI linkers to generate a neutral two-dimensional naphthalenediimide coordination network with all the ClO4− anions above or below this plane. Strong interlaminar anion-π interactions between the coordinated ClO4− anions and the imide rings of an adjacent layer lead to a three-dimensional supramolecular structure. Compound (I) exhibits reversible photochromic behaviour and photocontrolled tunable luminescence properties, which may originate from the photoinduced electron-transfer generation of radicals in the DPMNI ligand. [ABSTRACT FROM AUTHOR]

The reaction of CdCl2·2.5H2O with 1,1'-bis(3-carboxybenzyl)-4,4'-bipyridinium dichloride (H2L1·Cl2) or 4,4'-bis[(3-carboxypyridino)methyl]-biphenyl dichloride (H2L2·Cl2) in a dimethylformamide/methanol mixed-solvent system at room temperature, affording the complexes [(CdCl2)3(L1)3]n (1) and {[CdCl2(L2)(H2O)2]· 2H2O}n (2). They were characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction. Both 1 and 2 exhibit 1D coordination networks, which further stack into a 3D supramolecular structure by hydrogen bonding and π-π interactions. Furthermore, these two complexes exhibit different photochromic behavior in the solid state, which may originate from different charge-distributions of H2L1·Cl2 and H2L2·Cl2 ligands. [ABSTRACT FROM AUTHOR]

• Two isomeric metal-organic frameworks are prepared based on naphthalenediimide and naphthalenedicarboxylic acid. • Complexes 1 and 2 exhibit different photochromism and photocontrolled luminescence upon UV–Vis light irradiation. • Noncovalent interactions play an important role in the photochromic properties of MOFs. As a class of special type materials, photochromic metal-organic frameworks (MOFs) have attracted extensive attention because their usually show interesting color changes and coupled with the variation of some chemical and physical properties under light irradiation. In order to study the effect of secondary building on the photochromism of MOFs, two isomeric naphthalenediimide-based MOFs with different secondary building linkers, namely [Zn 2 (DPNDI)(2,6-NDC) 2 ] (1) and [Zn 2 (DPNDI)(1,4-NDC) 2 ] (2) (DPNDI = N, N '-di(3-pyridyl)-1,4,5,8-naphthalenediimide, 1,4-H 2 NDC = 1,4-naphthalenedicarboxylic acid, 2,6-H 2 NDC = 2,6-naphthalenedicarboxylic acid), were synthesized via solvothermal reaction and the structure were characterized by single-crystal X-ray diffraction, IR and TGA. Owing to the different C H···π interactions between the naphthalene moieties of dicarboxylic acid and electron-deficient DPNDI ligand, they showed different photochromic behaviors and photocontrolled luminescence upon ultraviolet-visible irradiation. Specifically, complex 2 was photochromic but complex 1 was not. The difference can be ascribed to the larger C H···π interaction in complex 1 than in complex 2. This work is expected to provide a new perspective for designing novel photochromic MOF materials Two isomeric naphthalenediimide-based MOFs with different secondary building linkers have been prepared, which exhibit different photochromic behaviors and photocontrolled luminescence upon ultraviolet-visible irradiation. [Display omitted] [ABSTRACT FROM AUTHOR]

A feasible method to construction multifunctional hybrid compounds is the incorporation of appropriate functional inorganic and organic components through self-assembly. Naphthalene diimides (NDIs) and polyoxometalates (POMs) are two versatile building blocks that have been used in many fields. In this paper, self-assembly of electron-deficient NDI ligand and POM resulted in an organic-inorganic hybrid compound, [Ce 2 (BINDI)(DMF) 8 ]·[Mo 6 O 19 ] (1), (H 4 BINDI = N , N ′-bis(5-isophthalic acid)-1,4,5,8-naphthalene diimide), with segregated Mo 6 O 19 2− polyanions and two-dimensional cationic coordination network. Because of the photochemical activities of organic and inorganic components, this hybrid compound exhibits interesting reversible photochromic behavior under ultraviolet–visible light irradiation. XRD, EPR, and XPS studies demonstrated that the photochromic behavior resulting from the coaction of NDI and Mo 6 O 19 2− polyanions. Moreover, this hybrid material shows excellent photocatalytic degradation activity toward the methylene blue (MB) dye under visible light irradiation. [Display omitted] • A polyoxometalate/naphthalenediimide hybrid structure is prepared. • Compound 1 shows fast-responsive reversible photochromism. • Photoinduced electron-transfer generate Mo5+ and NDI radicals. • Compound 1 exhibits excellent photocatalytic activity for degradation of methylene blue. [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]

• Two electron-transfer hybrid compounds based on electron-deficient naphthalene diimide and polyoxometalate were synthesized and characterized. • Complexes 1 and 2 exhibit the eye-detectable photochromic phenomenon. • Complexes 1 and 2 show good photocatalytic activity for degradation of carcinogenic dye BR9. Naphthalene diimide (NDI) derivatives and polyoxometalates (POMs) are two kinds of functional moieties with very different properties for applications in different fields. Two rare multifunctional inorganic-organic hybrid crystalline materials based on NDI and POM, have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analyses, and thermogravimetric analysis. These compounds show fast responsive reversible photochromic behaviors (within five minutes) under UV–vis light irradiation, which arise from the photoinduced electron transfer production of organic radicals rather than photoinduced isomerization or photolysis. Furthermore, due to presence the redox-active NDI and POMs, these unique hybrid materials are good heterogeneous photocatalyst for the degradation of carcinogenic organic dye basic red 9 (BR9) with a degradation rate of more than 86% within 120 min in the presence of H 2 O 2 under visible light irradiation. This work will provide a new perspective to explore multifunctional hybrid materials with useful photochromic and photocatalytic properties. [Display omitted] [ABSTRACT FROM AUTHOR]

• Four CPs based on alkaline-earth metal and viologen derivative are prepared. • Compounds 1 – 4 exhibit the reversible thermochromism and photochromism. • Compound 1 – 4 show vapochromic behavior in the presence of ethanediamine vapor. Due to their external stimuli responsive properties, chromic materials have attracted considerable interest in various fields. In this work, a series of alkaline-earth metal based coordination complexes constructed from viologen derivative, [Mg(H 2 O) 6 ·(bdpbpy)·H 2 O] (1), [Ca(bdpbpy)(H 2 O) 4 ] (2), [Sr(bdpbpy)(H 2 O) 4 ] (3), [Ba(bdpbpy)(H 2 O) 4 ] (4), (H 4 bdpbpy·2Cl = 1,1-bis(3,5-dicarboxyphenyl)-4,4-bipyridinium chloride) have been synthesized and characterized by elemental analyses, FT-IR spectroscopy, single-crystal X-ray diffraction, and thermogravimetric analysis. Because of electron transfer between the oxygen atom of carboxylate and bipyridinium moieties, compounds 1 – 4 exhibit reversible thermochromic and photochromic properties upon thermo treatment or Uv-vis irradiation. Due to presence of electron-deficient bipyridinium moieties (Lewis acidic sites), these compounds can be used as potential colorimetric sensor for ethanediamine vapor detection. The multi-responsive performances of compounds 1 – 4 can widen their applications in some particular systems that call for color changing properties of external stimuli. A series of viologen-based alkaline-earth metal coordination polymers were prepared by solvothermal reaction, which exhibit reversible thermochromic and photochromic properties upon thermo or Uv-vis stimulus. Moreover, these compounds exhibit prominent visual color change in the ethanediamine vapor [Display omitted]. [ABSTRACT FROM AUTHOR]

Naphthalene diimides (NDIs), a class of organic dyes with high photochemical activity and high redox activity, have attracted considerable interest attributing to their photoinduced electron transfer to form stable radical anions upon irradiation in the presence of electron donors. In this study, a naphthalenediimide-based ligand and different aromatic carboxylic acids self-assembled in the presence of zinc ions, forming three novel coordination polymers, [Zn 2 (DPMNI) (TPDC) 2 (1), [Zn (DPMNI) (BPC)] (2), Zn (DPMNI) (HBTC) (3) (DPMNI = N,N ′-bis(4-pyridylmethyl)-1,4,5,8-naphthalene diimide, H 2 TPDC = thiophene-2,5-dicarboxylic acid, H 2 BPC = 4,4′-biphenyldicarboxylic acid, H 3 BTC = 1,3,5-benzenetricarboxylic acid). These coordination polymers characterized by single-crystal X-ray diffraction, elemental analyses, IR spectroscopy, powder X-ray diffraction, and theromgravimetric analysis. Because of the presence of electron-deficient NDI moieties, they exhibit reversible photochromic properties. Furthermore, due to the different π–π interactions between the NDI moieties and aromatic carboxylic acid, compounds 1 – 3 exhibit different photosensitive properties. Moreover, the solvatochromic behaviour of compound 1 was also investigated. Three novel NDI-based coordination polymers were prepared by solvothermal reaction, which exhibit reversible photochromic properties and solvatochromic behaviour in the presence of different solvents. Image 1 • Three CPs based on electron-deficient naphthalene diimide dye are prepared. • Compounds 1–3 exhibit the visibly detectable photochromism. • Compound 1 exhibits solvatochromic behaviour in the presence of different solvents. • Solvatochromic effect of compound 1 arise from the intermolecular electron-transfer transition. [ABSTRACT FROM AUTHOR]

Naphthalene diimides (NDIs), a class of organic dyes with high photochemical activity and strong luminescent characteristics, have attracted considerable interest because of their photoinduced electron transfer to form stable radical anions in the presence of electron donors upon irradiation. In this paper, two novel metal–organic frameworks constructed from NDIs chromophoric and aromatic dicarboxylic acids, [Zn 2 (DPMNI)(NCA) 2 ·0.5DMF] (1), [Zn(DPMNI)(PTA)·DMF] (2), (H 2 NCA = 1,4-naphthalenedicarboxylic acid, H 2 PTA = p-phthalic acid, DPMNI = N,N ′-bis(4-pyridylmethyl)-1,4,5,8-naphthalene diimide, DMF = N,N ′-dimethylformamide), have been synthesized and characterized systematically. Because of the presence of electron-deficient NDI moieties, they exhibit reversible naked photochromic properties upon irradiation and photocontrolled luminescence due to the generation of NDI radicals. The carboxylate groups as electron donors play a key role in the photoinduced electron-transfer process, and the lone pair–π interaction is a preferred pathway to support photoinduced electron transfer from our work. This study has not only convincingly corroborated the relationship between the photoresponsive rate and non-covalent interactions, but also provided a feasible idea to design novel luminescence switching materials. Two novel NDI-based metal-organic frameworks were prepared by solvothermal reaction, which exhibit reversible naked photochromic properties upon irradiation. Moreover, their luminescence performance can be switched by UV–Vis light irradiation and standing in the air. Image 1 • Two MOFs based on electron-deficient naphthalene diimide dye are prepared. • 3D structure with 1D channel. • Complexes 1 and 2 exhibit the eye-detectable photochromism and photocontrolled luminescence. • The photoinduced radicals in complexes 1–2 have long-lived lifetime after irradiation. [ABSTRACT FROM AUTHOR]

The incorporation of photoresponsive component into metal-organic frameworks (MOFs) is intriguing because they can confer additional properties such as photomagnetic behavior, light-controlled electrical conductivity, and photocatalysis. Naphthalene diimide (NDI) is organic dye that absorbs visible light and have π-electron-deficient planes and photochemical characteristics. NDIs are ideal for creating photoactive MOF materials due to their ability of undergo reversible single-electron reduction and form stable radical anion. In this work, a photoactive MOF material, Mn 2 (BNDI) 2 (DMF) 3 (1) (H 2 BNDI = N,N' -bis(3-benzoic acid) naphthalenediimide), is fabricated and found to exhibit not only notable photochromism (light yellow to dark brown), but also reactive organic radical under ambient conditions. Complex 1 can act as an efficient electron-transfer photocatalyst for selective oxidation of 2,6-di- tert -butylphenol (2,6-DTBP) into various compounds under diverse reaction conditions, without the need for supplementary co-catalysts. Specifically, 2,6-DTBP is photocatalyzed to form 2,6-di- tert -benzoquinone and its dimer in methanol solution, 2,6-DTBP is converted to trimers and 3, 5-di- tert -butyl-4-hydroxybenzaldehyde in ethylene glycol with medium yield. This work will provide new perspective for the fields of NDI-based MOFs and photocatalysis. A photochromic MOF based on the NDI derivative has been developed for selective photocatalytic oxidative C–C coupling of 2, 6-di- tert -butylphenol to different products by controlling the reaction conditions. [Display omitted] • A photoactive MOF was prepared based on the naphthalene diimide derivative. • Complex 1 exhibit fast-responsive photochromism upon UV–Vis light irradiation. • Complex 1 shows selective photocatalytic oxidative 2, 6-di- tert -butylphenol to different products. [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]

Photochromic materials as a new class of multifunctional materials have received much attention owing to their potential applications in many fields. In order to investigate the electron-transfer photochromic behaviour of coordination polymers, two new coordination polymers based on the electron-deficient naphthalene diimide (NDI) and dicarboxylate ligand, namely [Zn 2 (DPNDI)(TPDC) 2 ] (1) [Cd 6 (DPNDI)(TPDC) 6 (DMF) 6 ] (2) (DPNDI = N,N ′-di(3-pyridyl)-1,4,5,8-naphthalene tetracarboxydiimide, H 2 TPDC = thiophene-2,5-dicarboxylic acid, DMF = N,N′-dimethylformamide), were synthesized under solvothermal condition and were characterized by elemental analysis, IR spectroscopy, thermogravimetric analyses, and single-crystal X-ray diffraction. Complex 1 is a three-dimensional coordination with rhombus channels, whereas complex 2 shows a sandwiched layer structure. Because of the presence of electron-deficient NDI moieties, complexes 1 and 2 can easily undergo photoinduced electron transfer and eye-detectable photochromic behaviour. Moreover, their luminescence can be switched by UV–Vis light irradiation and standing in the air. Two naphthalene diimide based coordination complexes exhibit the rare discoloured function of reversible photochromism. Interestingly, their luminescence performance can be switched by UV–Vis light irradiation and standing in the air. Image 1 • Two electron-transfer coordination polymer based on electron-deficient naphthalene diimide. • 3D structure with 1D channel. • Complexes 1 and 2 exhibit the eye-detectable photochromic phenomenon. • Their luminescence performance can be switched by UV–Vis light irradiation and standing in air. [ABSTRACT FROM AUTHOR]

The tunable luminescent materials based on photochromic reactions have received considerable interest due to its potential applications in switches and optical memory devices. However, constructing such materials with ideal properties remains a challenge. In this context, two rare viologen-based host guest materials, 2[MV]·[Zn 6 (PMA) 4 (H 2 O) 4 ] (1), 2[PBM]·[Zn 2 (PMA) 2 (H 2 O) 6 ] (2), (MV·2NO 3 ​= ​1,1'-dimethyl-(4,4'-bipyridine)-1,1'-diium dinitrate; PBM·2NO 3 ​= ​4,4'-(1,4-phenylene)bis(1-methylpyridin-1-ium) dinitrate; H 2 PMA ​= ​pyromellitic acid), have been prepared by encapsulating viologen derivatives into the anionic metal-organic frameworks produced from pyromellitic acid ligands and zinc cations. Due to the presence of photoactive guest MV2+/PBM2+ and the short O⋯N+ distances between the oxygen atom of carboxylate groups and pyridine ring of guest, both complexes display fast-responsive reversible naked photochromism from colorless to blue or yellow upon UV–Vis irradiation At the same time, these host-guest materials exhibit good fluorescence emission behavior and their fluorescence can be reversible modulation under light irradiation. These are rare examples of fluorescence switching materials based on host-guest system that involve the electron-transfer photochromic process. Two novel MOF-based host-guest compounds were prepared by incorporating the photoactive viologen derivatives into the anionic framework, which exhibit photochromism upon UV–Vis light irradiation and photocontrolled luminescence. [Display omitted] ● Two host-guest complexes are prepared by incorporating the viologen derivatives into the anionic MOFs. ● Complexes 1 and 2 exhibit fast-responsive photochromism upon UV–Vis light irradiation. ● Complexes 1 and 2 show good luminescent emission and reversible luminescence switching. [ABSTRACT FROM AUTHOR]