Viologen Ligand Research Articles

A novel Zn(II) coordination polymer based on viologen: Photochromism, photocontrolled luminescence, ammonia vapor sensing, and luminescent sensing

A novel Zn(II) coordination polymer, {[Zn4(BTEC)3][(3-BCBPY)2]·5H2O}n (compound 1), was synthesized based on viologen ligand (3-BCBPY·2Cl = 1,1′-bis(3-cyanobenzyl)-4,4′-bipyridinium chloride), benzoic acid (H4BTEC = 1,2,4,5-benzenetetracarboxylic acid) and ZnCl2. Single crystal X-ray diffraction analysis revealed that the Zn(II) ions are bridged by BTEC4− anions, giving rise to a 3D structure, with the 3-BCBPY2+ cations occupying the pores within the channels of compound 1. This compound displays photoactivity, undergoing significant color transformations under ultraviolet light irradiation. Furthermore, to gain a deeper theoretical understanding of the color-changing behavior of compound 1, time-dependent density functional theory (TDDFT) was employed. Additionally, compound 1 demonstrates ammonia vapor sensing capabilities, along with intriguing light-modulated luminescence properties. Notably, it also exhibits significant sensing abilities for Fe3+ and Cr2O72− ions, even at low concentrations (10−5 M). This compound not only showcases its applications in the realms of photochromism, but also explores its potential in ammonia vapor detection and ion sensing.

Syntheses and performance study of three POM-viologen compounds with photo- and electric-stimulation response

In recent years, stimulus responsive materials have received widespread attention. Under solvothermal conditions, three polyoxometalates-viologen organic–inorganic hybrid compounds were successfully constructed by combining a viologen ligand 1-(3-Nitro-benzyl)-[4,4′]bipyridinyl-1-ium bromide (1,3-nibipy·Br) with octamolybdate, namely [Cu2(1,3-nibipy)4(H2O)2(β-Mo8O26)2]·2H2O (1), [Cu2(1,3-nibipy)4(H2O)4(β-Mo8O26)]·(β-Mo8O26) (2) and (1,3-Hnibipy)2·(β-Mo8O26) (3). These three compounds can exhibit color changing properties under both light and electrical stimulation. Through characterizations of PXRD, FT-IR, UV–vis spectra, XPS, EPR, CV, and other tests, the photochromic and electrochromic properties of these three compounds are caused by the generation of viologen radicals. Compounds 1–3 have a rapid photoresponse efficiency and can be made into mixed matrix films for use as ultraviolet detectors. In addition, coated filter paper synthesized from acetonitrile and compounds can serve as an innovative erasable ink-free printing material medium, which is suitable for various erasable ink-free printing and anti-counterfeiting fields. We further investigated the electrochromic devices prepared from compounds 1–3, which achieved color change at a voltage of around −0.2 V and exhibited good stability after 500 cycles.

Two photochromic two-dimensional Zn(II)-MOFs based on a carboxybenzyl viologen ligand

Two new Zn(II) metal-organic frameworks (MOFs) {[Zn(Bpybc)0.5 (m-BDC)(H2O)]·2H2O}n (1) and {[Zn(H2Bpybc)(BTEC)(H2O)2]·H2O}n (2) have been successfully synthesized, where 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium dichloride (H2BpybcCl2) is used to react as the predesigned ligand with two kinds of aromatic carboxylic acids (1,3-benzenedicarboxylic acid = m-H2BDC, 1,2,4,5-benzenetetracarboxylic acid = H4BTEC) as the secondary building linkers. Both two compounds own two-dimensional (2D) layered structures. In addition, compounds 1 and 2 display reversible photochromism, which is associated with the generation of free radicals via photoinduced electron transfer. Simultaneously, the photomodulated fluorescent properties and their potential applications in ink-less and erasable printing were also studied.

Effect of lattice water on the photochromic property/photochromism of a Zn(II)-viologen coordination polymers

Electron transfer is crucial for the rapid response of viologen-based complexes and investigating the factors that affect electron transfer has always been a major challenge. Herein, a new viologen-based complex, formulated as {[Zn5(cbbbc)3(BTC)3(μ1,1-OH)(H2O)5]·22H2O}n, with a three-dimensional framework was successfully designed and synthesized by viologen ligand 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (Hcbbpy), trimesic acid (H3BTC) and Zn(NO3)2·6H2O. In particular, complex 1 does not exhibit photochromic properties. However, samples of complex 1 heated at 120 and 180 ℃ display tunable colors under UV light irradiation. The experimental results indicate that the compound's light response is less sensitive with higher water content in the lattice. The polarity and hydrogen bonding ability of lattice water in viologen-based complexes can interact with the donor of viologen, leading to a reduction in electron transfer. This study demonstrates the impact of lattice water on electron transfer in viologen-based complexes and offers insights for designing faster response complexes in the future.

Three multifunctional two-dimensional coordination polymers based on 1-(3-carboxybenzyl)-4,4′-bipyridinium ligand

By utilizing the carboxybenzyl viologen ligand 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (HBcbpy·Cl), 1,3,5-benzenetricarboxylic acid (H3BTC) and varying different metal ions, three new coordination polymers [Cd(Bcbpy)(HBTC)(H2O)·2H2O]n (1), [Zn(Bcbpy)(HBTC)(H2O)·2H2O]n (2) and [Co2(Bcbpy)2(HBTC)2(H2O)2·4H2O]n (3) have been synthesized and structurally characterized. Compounds 1 and 2 have identical two-dimensional (2D) coordination layered structure, while compound 3 features 2D+2D→2D structure. It is interesting that compounds 1 and 2 exhibit electron transfer photochromism, while compound 3 displays hydrochromism through dehydration. At the same time, considering the high stability and fast photo-response, the photo-modulated fluorescence and the inkless erasable printing capability are investigated.

Tunable photo/thermochromic properties of Cd(II)-viologen coordination polymers modulated by coordination modes for flexible imaging films and anti-counterfeiting.

Two photochromic Cd(II)-CPs were obtained based on the viologen ligand using different synthetic routes, named {[Cd4(p-BDC)4(CPB)2(H2O)2]·2H2O·EtOH}n (1) and {[Cd(p-BDC)(CPB)(H2O)]·(L)·DMF}n (2) (p-H2BDC = 1,4-benzene-dicarboxylate, HCPB·Cl = 1-(4-carboxyphenyl)-4,4'-bipyridinium·Cl, L = 2,4-dinitrochlorobenzene, and DMF = N,N-dimethylformamide), respectively. Due to different coordination modes, the two Cd(II)-CPs show different structures. Compound 1 exhibits a three-dimensional (3D) framework with bimetallic nodes, while compound 2 displays a 2-fold interpenetrated (4,4) net topology. Notably, the two Cd(II)-CPs exhibit substantial disparities in photo/thermochromism, which can be attributed to variations in donor-acceptor (D-A) distances arising from structural differences. Compound 1 showed visually sensitive photo- and thermochromic behavior due to multi-pathway electron transfer and short D-A distances, which is relatively rare in electron-transfer type photochromic systems. In contrast, 2 only demonstrates insensitive photochromic behavior, with a slight deepening of the color observed after 2 hours of UV light, which is due to the mono-pathway electron transfer and long D-A distance. Moreover, we first combined Cd(II)-viologen CPs with polydimethylsiloxane (PDMS) to prepare a 1@PDMS flexible UV imaging film. 1@PDMS exhibits excellent bendability and stretchability and maintains good photochromic properties after 100 bending cycles. To demonstrate the rapid color response and distinct color contrast of 1, its application in anti-counterfeiting is also demonstrated.

Photochromism of three complexes based on 1-(4-carboxybutyl)-4,4′-bipyridinium ligand

Based on the viologen ligand 1-(4-carboxybutyl)-4,4′-bipyridinium bromide (HCPbpyBr), three new complexes with different auxiliary ligands and metal ions have been prepared and structurally characterized, namely Ni(CPbpy)(H4BTEC)0.5(H2O)4·(BTEC)0.5·2H2O (1), Co(CPbpy)(H4BTEC)0.5(H2O)4·(BTEC)0.5·2H2O (2) and [Cd(CPbpy)(m-BDC)·2H2O]n (3) (1,2,4,5-benzenetetracarboxylic acid = H4BTEC, 1,3-benzenedicarboxylic acid = m-H2BDC). Complexes 1 and 2 have identical isolated structure, while complex 3 features a three-dimensional (3D) framework. Meanwhile, complex 3 exhibits electron-transfer (ET) UV and X-ray dual photochromism and photo-controlled luminescent properties, while photochromism is not observed in complexes 1 and 2. Additionally, complex 3 has the prospective application as an inkless and erasable printing material because of its excellent photochromic property.

Three functional Cd(II) coordination polymers constructed by the thiazolothiazole extended viologen ligand

Expanding the π-conjugated structure of traditional viologens by incorporating thiazole units to the bipyridine skeleton has attracted more and more attention. In this work, a rigid thiazolothiazole extended viologen ligand (TTVP, 2,5-bis (pyridinium-4-yl) thiazolo [5,4-d] thiazole propionate) has been used to constitute three new functional Cd(II) coordination polymers (CPs), {[Cd(TTVP)0.5(HBTC)(H2O)2]·2H2O}n (1), {[Cd(TTVP)0.5(p-BDC)0.5(p-HBDC)(H2O)]·3H2O}n (2), {[Cd(TTVP)0.5(m-BDC)]}n (3) by introducing different benzenecarboxylic acids as auxiliary ligands (H3BTC = 1,3,5-benzenetricarboxylic acid; p-H2BDC = 1,4-benzenedicarboxylic acid; m-H2BDC = 1,3-benzenedicarboxylic acid). The crystal structures and photochromic capabilities of 1−3 are studied. Both compounds 1 and 2 own one-dimensional (1D) chain-like structure, while compound 3 owns two-dimensional (2D) layered structure. As expected, compounds 1−3 show reversible photochromism due to electron-transfer (ET). In addition, the photo-controlled luminescent properties and the potential application as inkless and erasable printing media are also explored.

Three Anderson and octamolybdate based compounds modified by an asymmetric viologen: Photo-/thermo-chromic and luminescence properties

In this work, POM anions and a viologen ligand were combined to construct appealing electron transfer chromotropic materials. Three kinds of POM-viologen hybrids were obtained in hydrothermal environment, namely [Cu2(1,4-Mbby)2(H2O)6(TeMo6O24)]·H2O (1), [Co2(1,4-Mbby)2(H2O)6(TeMo6O24)]·H2O (2), [Cu2(1,4-Mbby)4(H2O)2(β-Mo8O26)2] (3, 1,4-Mbby·Cl = (1-(4-Methyl-benzyl)-[4,4′]bipyridinyl-1-ium)chloridate). Among them, compounds 1 and 2 are isostructural, showing an infinite inorganic chain with Anderson anions linked by Cu/Co atoms. The 1,4-Mbby suspend on both sides of this chain. Compound 3 exhibits a Mo8 dimer with four 1,4-Mbby as “arms”. POM anions and viologen ligands form a classical donor-acceptor structure, which can promote electron transfer. Therefore, under thermal stimulation, compounds 1–3 show reversible thermochromic properties. Under light stimulation, 1 and 3 have good reversible photochromic properties. Moreover, compound 1 can detect aniline, and 3 can detect ammonia and ethylenediamine through discoloration. Interestingly, compounds 1–3 show luminescence characteristics. Especially, the bright blue fluorescence of 1 can be observed under the irradiation of a 365 nm ultraviolet lamp. Meanwhile, compounds 1–3 have good fluorescence quenching effect under illumination or heating conditions. In other words, these compounds can quickly sense light or heat with color change. This work broadens the applications of POM/viologen compounds in the fields of discoloration and luminescence.

Tunable Chromic Properties of Viologen-Metal Polymers Modulated by Coordination Modes for Inkless Erasable Printing.

Inkless and erasable printing (IEP) based on chromic materials holds great promise to alleviate environmental and sustainable problems. Metal-organic polymers (MOPs) are bright platforms for constructing IEP materials. However, it is still challenging to design target MOPs with excellent specific functions rationally due to the intricate component-structure-property relationships. Herein, an effective strategy was proposed for the rational design IEP-MOP materials. The stimuli-responsive viologen moiety was introduced into the construction of MOPs to give it potential chromic behaviors and two different coordination models (i.e. bilateral coordination model, M1; unilateral coordinated model, M2) based on the same viologen ligand were designed. Aided by theoretical calculations, model M1 was recommended secondarily as a more suitable system for IEP materials. Along this line, two representative viologen-ZnII MOPs 1 and 2 with models M1 and M2 were synthesized successfully. Experiments exhibit that 1 does have quicker stimuli response, stronger color contrast and longer radical lifetime compared to 2. Significantly, the obtained 1-IEP media brightly inherits the excellent chromic characteristics of 1 and the flexibility of the paper at the same time, which achieves most daily printing requirements, as well as enough resolution and durability to be used in identification by smart device.

A novel photochromic complex based on a viologen ligand with rapid inkless and erasable printing, anti-counterfeiting and amine-selective responses

In this work, we have synthesized a novel complex {[Zn2(Bpybc)0.5(L)·H2O]·DMA·H2O}n (1) (H2BpybcCl2 = 1,1’-bis(4-carboxybenzyl)-4,4’-bipyridinium dichloride, H4L = 1,2,4,5-benzenetetracarboxylic acid) by solvothermal method. 1 has a 3D network stacking structure. 1 exhibits rapid and reversible photochromic behavior, showing the color change visible to the naked eye after being irradiated. 1 has been characterized by infrared spectroscopy, powder X-ray diffraction analysis, UV-vis absorption spectroscopy and electron paramagnetic resonance spectroscopy. The relationship between the structure of 1 and photochromic behavior has been discussed. 1 can be used as an anti-counterfeiting material and amine-selective response material at a fast speed. 1 can also be deposited on filter paper and used as an inkless and erasable printing medium. In addition, 1 has photomodulated fluorescence properties.

Crystal Structure and Photochromic Properties of Two Complexes based on 1‐(4‐carboxybenzyl)‐4,4′‐bipyridinium Ligand

AbstractSelecting different metal ions, two novel complexes {[Zn(BCbpy)(m‐BDC)(H2O)] ⋅ 2H2O}n (1) and [Co(H2O)6]0.5[Co0.5(BCbpy)(H2O)2](m‐BDC) ⋅ 3H2O ⋅ DMF (2) have been prepared and structurally characterized in the presence of the viologen ligand 1‐(4‐carboxybenzyl)‐4,4′‐bipyridinium (BCbpy) and 1,3‐benzenedicarboxylic acid (m‐H2BDC). The crystal structures and photochromic properties of two complexes have been investigated in this article. 1 possesses a two‐dimensional (2D) layered structure, while the structure of 2 is zero‐dimensional (0D). As expected, 1 and 2 were discovered to be photochromic accompanying electron transfer (ET). Interestingly, 1 can be dissolved in ethanol solution and deposited on filter paper, applied to a printing medium without ink.

A series of zinc coordination compounds showing persistent luminescence and reversible photochromic properties via charge transfer

Long persistent luminescence materials have wide application prospects in the fields of optical communication, sensors, and anticounterfeiting. Recently, some researchers have proved the feasibility of charge transfer effect in the construction of visible light excited room temperature phosphorescence (RTP) materials. However, materials with electronic effects require elaborate design to exhibit long-lived phosphorescence. Herein, a series of coordination compounds based on viologen ligand HL⋅Cl (4-carboxybenzyl)-4,4′-bipyridinium chloride) and Zn2+ with benzoic acid derivatives (o-, m-, p-phthalic acid) were reported. They exhibit not only reversible photochromic properties, but also long-lived persistent phosphorescence. Three complexes possess different structures through different auxiliary ligands with different optical physical properties. Complex 1 exhibits dynamic phosphorescence emission at low temperatures. Interestingly, we synthesized the first viologen complex (complex 2) with excitation wavelength dependent fluorescence, and the emission color gradually changed from blue to red with the increase of excitation wavelength. In addition, the applications of three complexes in data encryption and anticounterfeiting are further demonstrated. This work not only presents coordination compounds with dynamic afterglow materials, excitation wavelength- and time-dependent emission properties, but also provides a new strategy for the charge transfer effect in visible light-excited RTP materials.

Two new Zinc (II)-viologen coordination polymers: Syntheses, structures, and photochromic behaviors

The self-assembly of Zn (II) ions with monosubstituted viologen ligand 1-(3-carboxybenzyl)-4,4’-bipyridinium chloride (m-Hbcbpy·Cl) and 1,3,5-benzenetricarboxylic acid (H3BTC) under solvothermal conditions results in two coordination polymers, namely, {[Zn(bcbpy)Cl2]·H2O}n(1) and {[Zn(bcbpy)(HBTC)H2O]·2H2O}n(2). Due to the formation of viologen radicals, the two compounds exhibit a triple photochromic behavior to sunlight, UV light and blue light through electron transfer, and the sequence of light response time is 1 > 2. Photochromic mechanisms and the relationships between structures and properties have been discussed adequately. And using time-dependent density functional theory (TDDFT) to study the discoloration mechanism of compounds 1 and 2. More importantly, compound 1 can be deposited on filter paper and displays potential applications as an inkless printing material. In addition, the capabilities of compound 2 to act as anti-counterfeiting materials for QR codes have also been investigated.

A UV and X-ray dual photochromic Zn (II) metal-organic framework based on viologen: Photo-controlled luminescence and temperature-dependent phosphorescence

Nowadays, photoactive viologen units have been widely encapsulated in metal-organic frameworks and assembled into multifunctional materials with photochromism and other light regulating properties. A novel host-guest MOF material, {[Zn(bcbpy)0.5(IPA)]·CH3CN}n (1), has been constructed by a viologen ligand 1,1′-bis((3-carboxylatobenzyl)-4,4′-bipyridinium)-dichloride (H2bcbpy·2Cl), isophthalic acid (IPA) and zinc(II) chloride. Complex 1 exhibits UV and X-ray dual photochromism and photo-controlled luminescence properties. Complex 1 also exhibits a temperature-dependent phosphorescence from cyan to yellow when the temperature increases from 77 to 297 K. 1T will be obtained when 1 is heated in air at 230 °C for 30 min, 1T shows less sensitive photochromic property than 1 due to its longer C–H⋯O hydrogen bond distance for electron transfer pathway. In addition, complex 1 has the potential application as an inkless and erasable printing material due to the excellent photochromic property.

A layered Y(III)-viologen framework for efficient detection of nitrofurazone

Two-dimensional (2D) materials as sensors show the unique advantage in detection because of the functional sites on their surface are easier to contact with analytes. Based on the Hard-Soft-Acid-Base theory, a nitrogen-rich metal–organic framework, [Y3(ipbp)4(HCOO)4(H2O)2]·NO3∙8.5H2O (Y-MOF) was synthesized by solvothermal reactions of a viologen ligand bromide 1-(3,5-isophthalic acid)-4,4′-bipyridine (H2ipbpBr) and Y3+ ions. It shows a 2D layered structure in which these uncoordinated pyridine groups of ipbp− hang on both sides of the layer as Lewis basic sites and exhibits excellent chemical stability in aqueous solutions within a pH range from 1 to 13. Fluorescent experiment indicates that Y-MOF possesses a high sensitivity for nitrofurazone (NFZ) with a low detection limit of 0.77 ​μg/mL and a high quenching constant of 1.36 ​× ​104 ​M−1. The cycling tests confirm that this MOF can be easily recovered and repeatedly used without an obvious performance loss. Furthermore, Y-MOF can detect NFZ in irrigation water, river water, and milk, in which satisfactory recoveries ranged from 94.70% to 109.85% with low Removable Storage Device (RSD) of 0.55%–2.76%. These results demonstrate that Y-MOF can be used as a potential sensor for the practical detection of NFZ in water environment and food matrix.

UV and X-ray dual photochromism of a Zn(II)-viologen coordination polymer and its application in inkless and erasable printing

Multistimuli responsive materials based on the viologen coordination polymers have attracted much interest in the past few years due to the increasing demand for smart materials. In this paper, based on a viologen ligand 1-(3-carboxybenzyl)- 4,4′-bipyridinium chloride (Hcbbpy) and zinc(II) ion, a new crystalline complex, namely, {[Zn(cbbpy)Cl2]·H2O}n(1) has been designed and synthesized. In complex 1, every cbbpy ligand as a bridge links two Zn2+ ions via carboxylate O atom and pyridine N atom to extend to a 1D zigzag chain. The 1D chains are extended to 3D supramolecular structure through π···π stacking and hydrogen bonding. More importantly, 1 exhibits fast photochromic behaviors in response to UV and X-ray due to the formation of viologen radicals. Complex 1 also shows photo-modulated luminescence property in the solid state. In addition, complex 1 can be deposited on filter paper and displays the potential application as inkless print material.

A novel multifunctional Cd (II) coordination polymer based on viologen: photochromic, photocontrolled fluorescence and amines detection

• A novel multifunctional Cd-viologen coordination polymer has been synthesized. • The photochromic mechanism of 1 was investigated experimentally and theoretically. • Compound 1 has the ability to detect amines. • The photo-controlled luminescence properties of 1 has been explored. A novel coordination polymer, named [Cd(HCOO)(pbpy) 0.5 (bdc)(H 2 O)]·3H 2 O ( 1 ), based on a new flexible viologen ligand 1,1′-[1,4-phenylenebis(methylene)]-bis(4,4′-bipyridinium) dichloride ( pbpy·2Cl ), Cd(NO 3 ) 2 ·4H 2 O and terephthalic acid (H 2 bdc) was synthesized. Compound 1 has good photosensitive activity and can also respond to sunlight at room temperature. And using time-dependent density functional theory (TDDFT) to study the discoloration mechanism of compound 1 . Attractively, 1 has the ability to select and detect amines due to the electron-deficient properties of pbpy·2Cl . In addition, photocontrolled luminescence properties of 1 , during the coloration-decoloration process, has been researched.

Photo/Electrochromic Dual Responsive Behavior of a Cage-like Zr(IV)-Viologen Metal-Organic Polyhedron (MOP).

Stable stimulus-responsive materials are highly desirable due to their widespread potential applications and growing demand in recent decades. Despite the fact that viologen derivatives have long been known as excellent photochromic and electrochromic materials, the development of stable viologen-based multifunctional smart materials with short coloration times remains an exciting topic. To obtain photochromic and electrochromic dual responsive materials, embedding the viologen ligand into a robust metal oxide cluster to increase its stability and sensitivity is an effective strategy. Herein, a viologen-based metal-organic polyhedron (MOP) {[Zr6L3(μ3-O)2(μ2-OH)6Cp6]·8Cl·CH3OH·DMF} [Zr-MOP-1; H2L·2Cl = 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium dichloride, and Cp = η5-C5H5] was successfully prepared and characterized. It consists of trinuclear Zr-oxygen secondary building units and exhibits reversible photochromic and electrochromic dual responsive behaviors. As expected, the designed robust viologen-based nanocage with a V2E3 (V = vertex, and E = edge) topology can maintain its stability and rapid photo/electrochromic behaviors with an obvious reversible change in color from purple (brown) to green, mainly due to the enclosed cluster structure and the abundant free viologen radicals that originate from the effective Cl → N and O → N electron transfers. Spectroelectrochemistry and theoretical calculations of this Zr-MOP were also performed to verify the chromic mechanism.

Synthesis and properties of a novel photochromic metal organic framework for rapid amine selective sensing and Cr2O72− detection

A new photochromic metal organic frameworks (MOFs) have been synthesized by using a viologen ligand, named 1,1′-bis(3,5-carboxylatobenzyl)-(4,4′-bipyridinium) dichloride (H4bdcbpy•2Cl) and Cd(NO3)2·4H2O. This MOF (Cd-bdcbpy) features a three-dimensional (3D) framework structure, exhibiting photochromic properties under the irradiation of white light, blue light, UV light and heat with obvious color change from light yellow to dark green. Meanwhile, Cd-bdcbpy displays a visible color change to the naked eye when exposed to different organic amine molecules (ammonia, aniline, o-methylaniline and diphenylamine). Moreover, the detection of ammonia has been confirmed by the visual color changing phenomenon and luminescence quenching experiment and it can detect ammonia in very low concentrations (10-6 ​M). Attractively, through luminescence quenching, Cd-bdcbpy can be used as a multi response sensor for Cr2O72− anion in aqueous solution.