Viologen Moiety Research Articles

Cationic manganese(II)-based metal-organic framework constructed from viologen derivative with multifunctional properties

Utilizing the rigid and linear viologen carboxylic ligand as an organic linker, we have successfully synthesized and structurally characterized a multifunctional Mn-based cationic metal-organic framework (1). Compound 1 features a three-dimensional framework structure with a positively charged skeleton, wherein triangular pores accommodate [MnCl4]2− anions to preserve charge neutrality. Notably, compound 1 demonstrates a chemical chromism phenomenon, transitioning from yellow-brown to deep green upon exposure to ammonia. This color change is attributed to the nucleophilic attack of electron-rich ammonia molecules on the electron-deficient viologen moiety of viologen carboxylic ligand, leading to the formation of viologen radicals and charge transfer complexes. Moreover, compound 1 exhibits rapid and selective detection of antibiotics like metronidazole (MDZ) and dimetridazole (DTZ) via a competitive absorption-induced luminescence quenching process, featuring high quenching coefficients and low detection limits. Additionally, magnetic property investigations reveal predominant antiferromagnetic coupling between Mn(II) ions within compound 1.

Two novel Zn(II)-thiazolothiazole extended viologen complexes with photochromism, inkless and erasable printing and photo-modulated luminescence

The insertion of conjugated units between the two pyridine rings of traditional viologens is an effective way to regulate the stimulus response. Herein, the rigid thiazolothiazole extended viologen moiety (TTVP, 2,5-bis (pyridinium-4-yl) thiazolo [5,4-d] thiazole propionate) has been utilized in the preparation of photochromic materials, in which two novel complexes {[Zn (TTVP)0.5 (m-HBTC) (H2O)]·DMF·3H2O}n (1) and [Zn(H2O)6]0.5 (p-BDC)0.5·(TTVP)0.5 (2) (m-H3BTC = 1,2,4-benzenetricarboxylic acid, p-H2BDC = 1,4-benzenedicarboxylic acid), have been synthesized and characterized. Structural analysis exhibits that complex 1 features one-dimensional (1D) chain structure, while complex 2 exists as a discrete monomeric structure. As anticipated, both complexes exhibit reversible photochromic properties under UV irradiation because of electron transfer (ET). More importantly, the photo-controlled luminescent properties and the potential application as inkless and erasable printing media are also explored.

Electron transport kinetics for viologen-containing polypeptides with varying side group linker spacing

The role of the linker (the group connecting viologen moieties to peptide-based backbones) in electron transfer was studied. The backbone dictated the mechanism of electron transfer, whereas the linker length altered the rate of electron transfer.

Highly Soluble TEMPO‐Viologen Bipolar Molecule for Ultra‐Stable Aqueous Redox Flow Batteries

AbstractBipolar redox‐active organic molecule (BROM) is a feasible strategy to address the cross‐contamination issue of the electrolyte and, thus, improve the stability of the flow battery. Herein, a highly‐soluble BROM is developed by combining the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) and viologen moieties, and extensive characterizations are performed to evaluate its applicability in flow battery. Salient findings are as follows. First, the compound, viz. 1‐(1‐oxyl‐2,2,6,6‐tetramethylpiperidin‐4‐yl)‐1′‐(3‐(trimethylammonio)propyl)‐4,4′‐bipyridinium trichloride ((TPABPy)Cl3), features highly hydrophilic groups and yields a high aqueous solubility of 1.76 m. Second, the electrochemical result reveals that the (TPABPy)Cl3 displays two pairs of highly reversible peaks at −0.56 and 0.76 V, which respectively correspond to the viologen and TEMPO moieties. The electronic structure during the redox reactions is identified by both the density functional theory calculation and the electron paramagnetic resonance. Third, the flow battery fed with the 1.0 m (TPABPy)Cl3 solution delivers a high capacity of 25 Ah L−1 and a superior stability over the non‐bipolar counterparts. More to the point, the capacity decay can be effectively recovered by applying the polarity‐inversion rebalance strategy on the BROM. In summary, this work provides a molecular engineering way to rationally design a BROM to improve the capacity and stability of aqueous organic redox flow batteries.

An electron-deficient viologen metal-organic material for colorimetric and luminescence sensing of organic amines

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.

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.

Designing a high-potential metal-free viologen-based redox polymer for effective wiring of FAD-dependent glucose dehydrogenase

Metal-free organic redox mediators, whose redox potentials can be tuned according to the intended enzyme system and application, are emerging as alternative mediators for the design of improved enzyme-based biosensors and biofuel cells. We report a novel class of metal-free redox polymer containing a polymer-tethered dicyano viologen mediator for the immobilization of FAD-dependent glucose dehydrogenase (FAD-GDH) on graphite electrodes. Incorporation of strong electron-withdrawing cyano groups to the viologen moiety ensures the formation of high potential viologen-based redox polymer with an envisaged pH-independent redox potential close to 50 mV (vs Ag /AgCl/ 3 M KCl) and a negligible impact on oxygen reduction. The bioelectrode comprising of newly designed redox polymer and FAD-GDH showed enhanced electrocatalytic activity in the presence of glucose, confirming effective wiring of FAD-GDH, if embedded within the redox polymer.

Structure and photochromic properties of two cadmium coordination polymers derived from viologen ligands

AbstractTwo novel 1D Cd‐based coordination polymers (CPs) {[Cd(MQ)(HBTC)(H2O)2] ⋅ (H2BTC) ⋅ 4H2O}n (1) and {[Cd(AQ)(HBTC)(H2O)Br] ⋅ 2H2O}n (2) have been prepared in the reaction of Cd2+ with different viologen ligands such as 1‐methyl‐4,4′‐bipyridinium bromide (MQBr) or 1‐amyl‐4,4′‐bipyridinium bromide (AQBr) in the presence of 1,3,5‐benzenetricarboxylic acid (H3BTC). The Cd2+ ions are bridged by HBTC2− anions to take shape a 1D configuration for two CPs. Additionally, 1 and 2 both show photochromism due to the photoinduced electron transfer (ET) from electron‐rich O atoms to electron‐deficient viologen moieties. Compared with 2, compound 1 has a rapid photoresponsive rate. The different photochromic behaviors have been discussed adequately.

Two novel photochromic compounds based on a thiazolothiazole extended viologen derivative

In the last few years, more and more attention has been paid to the application of chromic materials, and photo-active viologen groups have been broadly assembled into functional materials with photochromism. However, the limited research conducted to date indicates that the extended viologen photochromic compounds are rarely reported. Herein, a rigid thiazolothiazole extended viologen moiety H2TTVPCl2 (2,5-bis (pyridinium-4-yl) thiazolo [5,4-d] thiazole propionate dichloride) is selected to construct two novel photochromic compounds, namely {[Zn(TTVP)0.5(BTEC)0.5(H2O)2]·2H2O}n (1) and [(H2TTVP)(H4BTEC)0.5]·(H2O)·2Cl (2). 1 has a two-dimensional (2D) layered structure, while 2 has a zero-dimensional (0D) structure. As expected, 1 and 2 display photochromic behavior of electron transfer. Furthermore, the photo-controlled luminescence and potential application as inkless and erasable printing media are also investigated.

Photoinduced electron transfer across the polymer-capped CsPbBr3 interface in a polar medium.

In-situ polymer capping of cesium lead bromide (CsPbBr3) nanocrystals with polymethyl acrylate is an effective approach to improve the colloidal stability in the polar medium and thus extends their use in photocatalysis. The photoinduced electron transfer properties of polymethyl acrylate (PMA)-capped CsPbBr3 nanocrystals have been probed using surface-bound viologen molecules with different alkyl chains as electron acceptors. The apparent association constant (Kapp) obtained for the binding of viologen molecules with PMA-capped CsPbBr3 was 2.3 × 107 M-1, which is an order of magnitude greater than that obtained with oleic acid/oleylamine-capped CsPbBr3. Although the length of the alkyl chain of the viologen molecule did not show any impact on the electron transfer rate constant, it influenced the charge separation efficiency and net electron transfer quantum yield. Viologen moieties with a shorter alkyl chain length exhibited a charge separation efficiency of 72% compared with 50% for the longer chain alkyl chain length viologens. Implications of polymer-capped CsPbBr3 perovskite nanocrystals for carrying out photocatalytic reduction in the polar medium are discussed.

Cationic Covalent Triazine Network: A Metal-Free Catalyst for Effective Acetylene Hydrochlorination

Vinyl chloride, the monomer of polyvinyl chloride, is produced primarily via acetylene hydrochlorination catalyzed by environmentally toxic carbon-supported HgCl2. Recently, nitrogen-doped carbon materials have been explored as metal-free catalysts to substitute toxic HgCl2. Herein, we describe the development of a cationic covalent triazine network (cCTN, cCTN-700) that selectively catalyzes acetylene hydrochlorination. cCTN-700 exhibited excellent catalytic activity with initial acetylene conversion, reaching ~99% and a vinyl chloride selectivity of >98% at 200 °C during a 45 h test. X-ray photoelectron spectroscopy, temperature programmed desorption, and charge calculation results revealed that the active sites for the catalytic reaction were the carbon atoms bonded to the pyridinic N and positively charged nitrogen atoms (viologenic N+) of the viologen moieties in cCTN-700, similar to the active sites in Au-based catalysts but different from the those in previously reported nitrogen-doped carbon materials. This research focuses on using cationic covalent triazine polymers for selective acetylene hydrochlorination.

Hydroxide ion-conducting viologen-bakelite organic frameworks for flexible solid-state zinc-air battery applications.

Adaptable polymer-based solid-state electrolytes can be a game-changer toward safe, lightweight flexible batteries. We present a robust Bakelite-type organic polymer covalently decked with viologen, triazine, and phenolic moieties. Its flexible structure with cationic viologen centers incorporates counter-balancing free hydroxide ions into the polymeric framework. By design, the aromatic groups and heteroatoms in the framework can be activated under an applied potential to prompt a push-pull drive, setting off the towing of hydroxide ions via weak electrostatic, van der Waals, and hydrogen-bond interactions. The frontier orbitals from a DFT-modeled structure certify this. The hydroxyl-polymer requires minimal KOH wetting to maintain a humid environment for Grotthuss-type transport. The hydroxide ion conductivity reaches a value of 1.4 × 10-2 S cm-1 at 80 °C and 95% RH, which is retained for over 15 h. We enhanced its practical utility by coating it as a thin solid-state separator-cum-electrolyte on readily available filter paper. The composite exhibits a conductivity of 4.5 × 10-3 S cm-1 at 80 °C and 95% RH. A zinc-air battery (ZAB) constructed using this polymer-coated paper as electrolyte yields a maximum power density of 115 mW cm-2 and high specific capacitance of 435 mA h g-1. The power density recorded for our ZAB is among the best reported for polymer electrolyte-based batteries. Subsequently, the flexible battery fabricated with IISERP-POF11_OH@FilterPaper exhibits an OCV of 1.44 V, and three batteries in series power a demo traffic signal. To underscore the efficiency of hydroxide ion transport through the complex multifunctional backbone of the polymer, we calculated the diffusion coefficient for OH- (Exp: 2.9 × 10-5 cm2 s-1; Comp. 5.2 × 10-6 cm2 s-1) using electrochemical methods and MD simulations. Climbing-edge NEB calculations reveal a large energy barrier of 2.11 eV for Zn2+ to penetrate the polymer and identify hydroxide ions within the polymer, suggesting no undesirable Zn2+ crossover. Our findings assert the readily accessible C-C-linked cationic polymer's capacity as a solid-state electrolyte for ZABs and any anion-conducting membrane.

Five novel supramolecular assemblies constructed from the thiazolothiazole extended viologen moiety

Five novel supramolecular assemblies based on the thiazolothiazole extended viologen moiety have been obtained, showing reversible photochromic behavior.

Photo-induced change in alignment of mesogens using reduction of viologens as a trigger

Liquid crystals (LCs), whose refractive index can be changed by light irradiation, can be used as photoresponsive optical materials. In this study, an LC viologen was proposed as a novel photoresponsive compound that induced a change in the alignment of LC molecules (mesogens). An extended viologen with an asymmetric core, that exhibits a low-order LC phase at room temperature, was mixed with the well-known nematic LC compound (5CB) to prepare homogeneously aligned films. The change in the alignment of the mesogens was successfully induced by triggering a one-electron reduction reaction of the viologen moieties by light irradiation.

Planar Viologen-Based Crystalline Compounds Showing Heat-Induced Electron Transfer and Thermochromism

Heat-induced electron transfer (ET) is desirable for some applications, such as thermal/photothermal catalysis, thermochromic antifake, and thermal control of molecular recognition, but needs to be avoided for photochromic or electrochromic windows and other devices. However, to date, the key structural factors of heat-induced ET for viologen compounds are still unclear. This work reveals that the planar structures of viologen moiety may be an important factor for heat-induced ET and thermochromism, through the summarization of a structural law from established thermochromic viologen compounds and the experimental verification using three known compounds with near-planar viologen moieties. Hence, this work contributes to enhance the probability of finding thermochromic viologen compounds with heat-induced electron transfer process.

A Multifunctional Coordination Polymer Constructed by Viologen Derivatives: Photochromism, Chemochromism, and MnO4- Sensing.

A multifunctional Cd-based coordination polymer based on a viologen derivative and a secondary carboxylic ligand, namely, {[Cd2(bcbp)(pta)2 (H2O)]·2H2O}n (1, H2bcbpCl2 = 1,1'-bis(4-carboxyphenyl)-(4,4'-bipyridinium) dichloride, H2pta = p-phthalic acid), has been solvothermally synthesized and structurally characterized. Compound 1 is a 3D framework built on {Cd2(pta)2 (H2O)}n net with square channels which intalls bcbp ligands at the diagonal position of the two adjacent square channels. Notably, compound 1 exhibits a reversible photochromic transformation between yellowish gray and dark green under xenon light irradiation, which should be attributed to the formation of free viologen radicals. Furthermore, compound 1 also displays a chemochromic phenomenon from yellowish gray to dark green after exposure to ammonia and hydrazine, which could be ascribed to the generation of viologen radicals and charge-transfer complexes triggered by nucleophilic attack of electron-rich ammonia and hydrazine molecules to the electron-deficient viologen moiety in the bcbp ligand. Moreover, compound 1 is capable of quickly and selectively detecting MnO4- with a high quenching coefficient and a low limit of detection via a luminescent quenching process caused by the competitive absorption of excitation energy.

Photoinduced electron transfer in host-guest interactions of a viologen derivative with a didansyl-pillar[5]arene

With the goal of understanding the electron transfer mechanism of fluorophore-functionalized pillararenes, a pillar[5]arene bearing two dansyl fluorophore moieties at the opposite rims of its cavity has been synthesized, and the behavior of such a new host molecule has been thoroughly investigated in the presence of an N,N′-di-(6-bromohexyl)-viologen derivative. 1H NMR, NOESY and DOSY experiments demonstrated that the pillar[5]arene recognizes the viologen derivative, forming a 1:1 host-guest complex by including one of the two bromoalkyl chains within its π-rich cavity. Photophysical and electrochemical studies revealed that, upon guest addition to the host, the fluorescence intensity of the complex is progressively quenched by a photoinduced electron transfer process (PET) from one of the dansyl groups of the host to the viologen moiety of the guest.

Zinc(ii) phthalocyanine–viologen dyads: synthesis, electrochemistry, spectroelectrochemistry, electrodeposition, and electrochromism

Electrochromic properties have been enriched by combining the anodic colorant zinc phthalocyanine and cathodic colorant viologen moieties into a dyad system via a flexible chain.

Supramolecular Polymerization Powered by Escherichia coli : Fabricating a Near-Infrared Photothermal Antibacterial Agent in Situ

Supramolecular Polymerization Powered by <i>Escherichia coli</i> : Fabricating a Near-Infrared Photothermal Antibacterial Agent in Situ

Viologen-Immobilized 2D Polymer Film Enabling Highly Efficient Electrochromic Device for Solar-Powered Smart Window.

Electrochromic devices (ECDs) have emerged as a unique class of optoelectronic devices for the development of smart windows. However, current ECDs typically suffer from low coloration efficiency (CE) and high energy consumption, which have thus hindered their practical applications, especially as components in solar-powered EC windows. Here, the high-performance ECDs with a fully crystalline viologen-immobilized 2D polymer (V2DP) thin film as the color-switching layer is demonstrated. The high density of vertically oriented pore channels (pore size ≈ 4.5nm; pore density ≈ 5.8 × 1016 m-2 ) in the synthetic V2DP film enables high utilization of redox-active viologen moieties and benefits for Li+ ion diffusion/transport. As a result, the as-fabricated ECDs achieve a rapid switching speed (coloration, 2.8 s; bleaching, 1.2 s), and a high CE (989 cm2 C-1 ), and low energy consumption (21.1 µW cm-2 ). Moreover, it is managed to fabricate transmission-tunable, self-sustainable EC window prototypes by vertically integrating the V2DP ECDs with transparent solar cells. This work sheds light on designing electroactive 2D polymers with molecular precision for optoelectronics and paves a practical route toward developing self-powered EC windows to offset the electricity consumption of buildings.